To examine what happens when that confinement is reduced, the investigators used mice with a deficiency in Gα13-dependent G-protein-coupled receptor signaling. This experimental defect allowed B cells to migrate between germinal centers in the same lymph node, providing a model in which the effects of de-confinement could be assessed. The study focused on mouse lymph nodes and their germinal-center B cells rather than directly testing human antibody responses.

The team used multicolor clonal lineage tracing to compare the organization of B-cell lineages. In reporter mice, individual germinal centers can acquire distinguishable color palettes as different lineages accumulate. Germinal centers in confinement-defective lymph nodes, however, became homogenized in this reporter pattern, showing minimal diversification in their color palettes relative to one another.

The result indicates that loss of confinement reduced the separation of distinctive clonal histories that otherwise developed among individual germinal centers. The researchers detected greater clonal crossover between neighboring germinal centers in lymph nodes where the centers were dispersed. In these nodes, the overall germinal-center B-cell repertoire was less diverse, and the distribution of clones became more strongly skewed toward top clones.

The findings therefore link inter-center exchange with reduced repertoire diversity and increased concentration of the response in a limited set of lineages. Lymph nodes containing de-confined germinal centers more strongly favored clones responding to accessible epitopes, while clones binding to other portions of the antigen were reduced. These results suggest that confinement supports antibody breadth by moderating the spread of dominant clones and preserving unique trajectories in individual germinal-center responses.

Subject of Research: Mouse germinal-center confinement, B-cell clonal diversity and immunodominance

Article Title: Spatial confinement promotes germinal center diversity and tempers immunodominance

Article References: Chen, K. Y., Hu, K. H., Kirthivasan, N., Rao, A., Schwan, N., An, J., Xu, Y., Peng, V., Magnen, M., Huang, S., Yin, Q., Ghose, D., Alexander, C., Smerczynski, J., Meyer-Hermann, M., Krummel, M. F., Mallajosyula, V., Lingwood, D., & Cyster, J. G. (2026). Spatial confinement promotes germinal center diversity and tempers immunodominance. Nature Immunology. https://doi.org/10.1038/s41590-026-02698-x

Image Credits: AI Generated

DOI: 10.1038/s41590-026-02698-x

Keywords: germinal centers, B cells, antibody diversity, immunodominance, clonal tracing, spatial sequencing, lymph nodes, antigen recognition, cell confinement, Spatial, confinement, promotes

The study drew on 4,209 volunteers recruited between January 2022 and December 2023 through the First Affiliated Hospital of Guangzhou Medical University (Loudi Hospital), including 2,898 women and 1,311 men. All participants were healthy controls screened to exclude active immune disorders, malignancies, recent infections, and immunosuppressive therapy. Researchers measured ten immune parameters in peripheral blood using flow cytometry, covering total T cells, CD4+ and CD8+ T cell subsets, the CD4/CD8 ratio, B cells, natural killer cells, NKT cells, and expression of the checkpoint molecule PD-1 on several cell types.

Because raw immune measurements rarely follow a normal distribution, the team applied Box-Cox transformations and Tukey’s method to remove outliers before analysis, leaving between 4,123 and 4,204 reference individuals per parameter. Age-related trends were then examined with sex-stratified smooth curves and non-parametric tests, and a 1:1 propensity score matching procedure was used to build age-balanced male and female cohorts for direct comparison.

The headline finding is a sharp sexual dimorphism in B cell dynamics. In women, the proportion of CD19+ B cells rose with age, while in men it fell, producing opposite trajectories that the authors link tentatively to hormonal regulation and X-chromosome-encoded immune genes. After age matching, women had significantly higher B cell percentages than men, but a stratified analysis showed this gap was not significant before age 50 and only emerged after menopause, pointing to the postmenopausal window as the critical period.

T cell subsets told an equally striking story. In women, CD4+ helper T cells and the CD4/CD8 ratio climbed to a peak in the 55-to-59-year age group, while CD8+ cytotoxic T cells declined steadily across the lifespan. The authors describe this as a “scissor-like” pattern that closely parallels the abrupt drop in estrogen levels around menopause. Because hormone levels were not directly measured, they caution that this mechanistic interpretation remains speculative, but the timing of the immune shift aligns closely with the typical age of menopause as defined by the STRAW+10 staging framework.

PD-1, an immune checkpoint molecule best known as the target of modern cancer immunotherapies, showed a complex, cell-type-specific pattern. Women had lower PD-1 expression on CD4+ T cells and NK cells but higher PD-1 on CD8+ T cells, and the proportion of CD8+ PD-1+ cells showed a transient peak in the 60-to-64-year group. The authors suggest this may mark a window of heightened functional dysregulation in cytotoxic immunity, with potential relevance for how immune checkpoint status should be interpreted across demographic groups.

Innate immunity shifted as well. Natural killer cell percentages increased with age in both sexes, but the rise was markedly steeper in men, and the fraction of NK cells expressing PD-1 declined significantly with age in women. NKT cells, by contrast, showed no significant age-related trend. After age matching, women had higher NK cell and NKT cell proportions than men, alongside their higher CD4/CD8 ratios, reinforcing the picture of two distinct immune aging trajectories.

The findings carry practical implications. Because women generally mount stronger vaccine responses but suffer more autoimmune disease, and because PD-1 expression shapes anti-tumor immunity and postoperative infection risk, the authors argue that both sex and reproductive stage should be factored into studies of immune aging and into interventions such as vaccination strategies for middle-aged women. The observed B cell persistence in older women may represent a distinctive adaptive feature of female immunosenescence, though its consequences for humoral immunity remain to be tested.

The study has clear limitations. It is cross-sectional, so it captures age-related differences between individuals rather than tracking immune changes within the same person over time. Without menstrual records or hormone measurements, the researchers could not formally stage participants under STRAW+10 and instead used age groups as an approximation, meaning the 50-to-54-year group inevitably mixes perimenopausal and early postmenopausal women. The authors call for longitudinal studies that pair hormone monitoring with systematic reproductive staging to confirm whether the menopausal transition itself drives the immune shifts observed here.

Even with those caveats, the scale of the cohort and the consistency of the sex differences make a strong case that immunosenescence is not a single process but two, diverging sharply at midlife. For a field in which clinical trial populations and reference ranges have historically skewed male, the message is that middle-aged women may need their own immunological yardsticks, and that menopause deserves a place alongside chronological age as a variable in immune research.

Subject of Research: Sex differences in lymphocyte subset changes during the menopausal transition and immunosenescence

Article Title: Dynamic Shifts in Lymphocyte Subsets During the Menopausal Transition and Sexual Dimorphism in Immunosenescence

Article References: Xuan, C., He, L., Bohan, Z., Junming, X., Qingchao, L., & Junting, H. (2026). Dynamic Shifts in Lymphocyte Subsets During the Menopausal Transition and Sexual Dimorphism in Immunosenescence. Immunity, Inflammation and Disease, 14(10), Article e70558. https://doi.org/10.1002/iid3.70558

Image Credits: AI Generated

DOI: 10.1002/iid3.70558

Keywords: immunosenescence, menopause, lymphocyte subsets, PD-1, T cells, B cells, natural killer cells, sexual dimorphism, flow cytometry, estrogen, immune aging, propensity score matching

Germinal centers are among the most elegant structures in immunology. Within the secondary lymphoid organs of mammals and birds, these specialized microenvironments provide the stage on which B cells proliferate, mutate the genes encoding their antibodies, and compete for survival in a Darwinian selection process. Only the B cells that produce the highest-affinity antibodies emerge victorious, differentiating into long-lived plasma cells that secrete protective antibodies or memory B cells that stand guard against future infection. This process, known as affinity maturation, is what allows vaccines and natural infections to generate durable, high-quality immune protection.

For decades, the prevailing view held that bona fide germinal centers first appeared roughly 200 million years ago in birds, marking what many considered a critical evolutionary milestone in the development of mucosal adaptive immunity. Teleost fish, the most species-rich group of vertebrates, lack the classical lymphoid architecture found in mammals and birds. They possess no lymph nodes, no organized spleen follicles of the mammalian type, and no pre-formed anatomical niches that resemble the germinal centers of warm-blooded vertebrates. This absence raised a fundamental and long-standing question: can the mucosal tissues of fish independently organize immune responses of comparable sophistication, or are such reactions the exclusive invention of more recently evolved lineages?

The Chinese research team, led by investigators at the Institute of Hydrobiology, tackled this question by studying the gut immune response of common carp following viral infection. Their model organism was challenged with spring viremia of carp virus, a pathogen that was delivered directly into the digestive tract by oral gavage. This infection route triggered clear pathological changes in the gut and provoked a strong local immune response, providing the researchers with a window into how the fish intestinal immune system mobilizes against a real viral threat.

The technical approach combined three complementary methods: single-cell RNA sequencing to profile gene expression in individual cells, fluorescence in situ hybridization to localize specific transcripts within tissue sections, and immunofluorescence staining to visualize proteins and cell populations. Using this integrated toolkit, the researchers identified previously unknown lymphoid aggregates within the intestinal lamina propria. They named these structures gut-associated germinal center-like structures, abbreviated GaGCLs, and their molecular and cellular features turned out to be strikingly familiar.

At the molecular level, the GaGCLs displayed spatial gradients of expression for the chemokine receptors CXCR4 and CXCR5, a hallmark of the dark zone and light zone organization that characterizes mammalian germinal centers. B cells within these structures showed elevated expression of AICDA, the gene encoding activation-induced cytidine deaminase, the enzyme responsible for introducing mutations into antibody genes, and MKI67, a canonical marker of active cell proliferation. The structures also harbored IgM-positive B cells specific for spring viremia of carp virus, which accumulated in response to infection. Most tellingly, the researchers observed extensive B cell proliferation occurring alongside significant apoptosis within the GaGCLs of infected fish, a combination that mirrors the brutal selection process at the heart of genuine germinal center reactions.

Single-cell transcriptomics also revealed the communication networks that coordinate these responses. The analysis identified key ligand-receptor interactions between T cells and B cells that are known to drive germinal center reactions in mammals, including ALCAM-CD6, TNFSF14-TNFRSF14, TGFB1-TGFBR3, and TNFSF14-LTBR. The researchers further identified T follicular helper-like cells, the specialized T cell population that shepherds B cells through affinity maturation in mammalian germinal centers, and documented extensive interactions between these cells and the germinal center-like B cells of the carp gut. Together, these conserved molecular programs and cell-cell communication networks argue that the functional logic of the germinal center reaction is deeply conserved across vertebrate evolution.

The functional consequences of these structures became apparent when the researchers tracked the immune response over time. Following primary infection, germinal center-like B cells within the GaGCLs gradually gave rise to memory-like B cells. When the fish were subsequently rechallenged with the virus, these memory-like cells were associated with increased numbers of plasma cells, expanded populations of IgM-positive B cells, and stronger antibody responses. In other words, the gut-associated structures of the carp did not merely mount a one-time reaction; they appeared to contribute to the establishment and recall of mucosal B cell memory, the very property that makes germinal centers so valuable to long-term immunity.

Perhaps the most conceptually significant aspect of the study is what it implies about the relationship between immune function and anatomical form. The GaGCLs were not permanent fixtures of the carp intestine. Instead, they were dynamically assembled in response to pathogen stimulation, forming temporary organizations within the lamina propria when the viral threat demanded them. This demonstrates that a functional germinal center-like immune response can be built without the structural framework of conventional secondary lymphoid organs. The immune system, in this view, does not require a pre-existing anatomical blueprint; it can construct the necessary architecture on demand, cell by cell, in response to infection.

The researchers summarize this principle as function preceding form, a model in which the functional components of sophisticated germinal center-like responses emerged in vertebrate mucosal tissues before the evolution of highly organized secondary lymphoid structures. If correct, this reframes the evolutionary narrative of adaptive immunity. Rather than viewing germinal centers as a relatively recent innovation of birds and mammals, the carp data suggest that the core molecular and cellular machinery of affinity maturation has ancient roots, traceable to early teleost lineages, and that later evolution added the permanent anatomical housing rather than the functional program itself. The gut cell types and functional characteristics observed in the fish, the team notes, are similar to those of mammals, reinforcing the idea of a shared and deeply conserved mucosal immune toolkit. For immunologists and evolutionary biologists alike, the carp intestine now stands as a living record of how one of biology’s most refined defense systems came to be, and it may inspire new searches for germinal center-like reactions in other organisms long assumed to lack them.

Subject of Research: Germinal center-like immune structures in the teleost fish gut and the evolution of mucosal adaptive immunity

Article Title: Teleost gut harbors germinal center-like structures

Article References: Teleost gut harbors germinal center-like structures. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: germinal centers, teleost fish, common carp, mucosal immunity, B cells, adaptive immunity, single-cell RNA sequencing, evolution, viral infection, IgM antibodies, memory B cells, gut-associated lymphoid tissue

The stakes are high. Most patients with IgA nephropathy progress to kidney failure within ten to fifteen years of disease onset, making the condition one of the leading causes of end-stage kidney failure globally. The disease is a mesangioproliferative glomerulonephritis characterized by dominant deposition of IgA in the mesangial region of the glomeruli, the filtering units of the kidney. The current multi-hit model holds that patients first accumulate elevated circulating levels of galactose-deficient IgA1, an antibody subtype whose O-linked glycans in the hinge region lack terminal galactose. This aberrant antibody then forms high-molecular-weight immune complexes with IgG and IgA antibodies directed against it, and these complexes deposit in the mesangium, triggering inflammation and progressive scarring. Because production of the galactose-deficient antibody is considered the first and central hit, therapeutic strategies targeting its cellular sources are now under active development.

The pathogenic molecule was identified through elegant analytical chemistry. In 1997, Tomana and colleagues analyzed the O-glycan structures of serum IgA1 by gas chromatography and found IgA1 with galactose-deficient O-glycans in the hinge region, subsequently termed Gd-IgA1. The galactose deficiency exposes N-acetylgalactosamine, which can be detected with the GalNAc-specific lectin Helix aspersa agglutinin. Hiki and colleagues later used mass spectrometry to show that IgA1 deposited in the glomeruli of patients is also characterized by reduced galactosylation and sialylation. The review authors generated the monoclonal antibody KM55, which specifically recognizes the hinge region of human Gd-IgA1, and directly demonstrated that glomerular IgA deposits in IgA nephropathy consist predominantly of the galactose-deficient form. IgA deposition in the mesangium alone, however, is not specific to the disease and can also be observed in lupus nephritis, hepatitis B virus-associated nephropathy, and liver cirrhosis, which is why qualitative abnormalities of the antibody have become such an important research focus.

Evidence points to the mucosal immune system as the predominant site where pathogenic IgA-producing B cells are primed. Glomerular IgA deposits contain J chain, indicating a polymeric form, and secretory component has been detected in a subset of deposits, suggesting mucosal origin. Clinically, many patients experience episodic gross hematuria after upper respiratory or gastrointestinal infections, and interventions targeting mucosal immunity, including tonsillectomy and the targeted-release budesonide formulation Nefecon, improve renal outcomes. A genome-wide association study has identified susceptibility loci related to mucosal immunity, including CARD9 and HORMAD2, which are also associated with inflammatory bowel disease. Within mucosa-associated lymphoid tissue, the tonsils are considered important sites in the nasopharynx-associated compartment, while Peyer’s patches in the terminal ileum are key within the gut-associated compartment. The predominant compartment involved may vary across geographical regions.

Within mucosal lymphoid tissues, B-cell class switch recombination and differentiation into IgA-producing cells are regulated by germinal center-dependent responses and signaling pathways involving toll-like receptors, APRIL, and BAFF. In the germinal center pathway, exogenous antigens taken up by dendritic cells activate naive CD4-positive T cells through MHC class II-dependent presentation, and a subset of these T cells differentiates into follicular helper T cells. Tfh cell-derived CD40 ligand and transforming growth factor-beta play central roles in class switching to IgA, while interleukin-21 and interleukin-10 support the expansion, survival, and differentiation of IgA-switched B cells into antibody-secreting cells. In IgA nephropathy patients, increased frequencies of activated Tfh cells and elevated serum IL-21 levels are associated with higher serum Gd-IgA1 concentrations, and circulating Tfh cell-derived IL-21 correlates with disease activity including the degree of proteinuria. Definitive evidence that germinal center reactions represent the predominant source of pathogenic Gd-IgA1-producing cells is still lacking, but the circumstantial case is strong.

Toll-like receptor signaling provides a second route to aberrant antibody production. TLR9, which recognizes unmethylated CpG DNA from microorganisms, promotes Gd-IgA1 production through induction of interleukin-6 and APRIL and exacerbates glomerular IgA, IgG, and C3 deposition as well as kidney injury in gddY mice, a spontaneous murine model of the disease. TLR9 polymorphisms and aberrant expression have been associated with disease severity and therapeutic responsiveness, and tonsillar TLR9 expression has been linked to the efficacy of steroid therapy combined with tonsillectomy. TLR7, which recognizes microbial single-stranded RNA, similarly aggravates the disease by promoting Gd-IgA1 production, with expression associated with IL-6 production and correlated with APRIL expression in patient tonsils. Consistent with these findings, hydroxychloroquine has produced sustained reductions in proteinuria, and suppression of TLR7/9 signaling has been suggested as one mechanism underlying its therapeutic effects. TLR4, activated by lipopolysaccharide from Gram-negative bacteria, has been proposed to contribute through the TLR4/MyD88/NF-kappaB pathway in response to gut dysbiosis.

APRIL and BAFF, whose expression can be enhanced by toll-like receptor signaling, play pivotal roles in differentiating B cells into IgA-producing cells. Three receptors mediate their signaling: BAFF receptor, which specifically binds BAFF, and the two shared receptors TACI and BCMA. BAFF signaling through BAFFR is critical for the survival of immature and naive B cells, whereas APRIL signaling through TACI and particularly BCMA becomes increasingly important as B cells differentiate into plasmablasts and plasma cells. Consequently, BAFF is thought to predominate in the survival of immature and mature B cells, while APRIL is more closely involved in IgA class switching and the maintenance of antibody-secreting cells. Genome-wide association studies have identified APRIL- and TACI-related loci as susceptibility loci for IgA nephropathy, and recent clinical trials showing that APRIL/BAFF-targeted therapies markedly reduce serum Gd-IgA1 levels and proteinuria further support the role of this pathway in sustaining pathogenic production.

Where the Gd-IgA1-producing cells reside is essential to understanding the chronic course of the disease. Patients exhibit increased numbers of polymeric IgA1-positive plasma cells and IgA1-producing cells in the bone marrow, and experimental studies have shown amelioration of the disease following bone marrow transplantation in murine models, with clinical cases reporting remission after bone marrow or peripheral blood stem cell transplantation for hematologic disorders. Antigen-specific lymphocytes and antigen-presenting cells undergo continuous trafficking between mucosal tissues and bone marrow in humans, leading to the proposal that dysregulation of the mucosa-bone marrow axis promotes mis-homing of Gd-IgA1-producing cells aberrantly primed in mucosal lymphoid tissue to the bone marrow, where they differentiate into long-lived plasma cells that continuously produce the molecule. Recent studies have also identified infiltration of B cells and plasma cells within renal tissues, where intrarenal B cells express TLR7 and produce IL-6, raising the possibility of local Gd-IgA1 production. Circulating Gd-IgA1-expressing B cells in peripheral blood carry preferentially lambda light chains, consistent with mesangial IgA deposits, and express mucosal homing receptors.

Therapeutic strategies now target both the mucosal abnormalities that initiate pathogenic production and specific stages of B-cell differentiation that sustain it. Tonsillectomy alone reduced serum Gd-IgA1 levels and improved hematuria in 59 percent of patients, and steroid therapy combined with tonsillectomy demonstrated higher rates of proteinuria remission, 65.7 versus 35.0 percent, and hematuria remission, 77.1 versus 45.0 percent, compared with steroid therapy alone. Nefecon, a targeted-release formulation of budesonide delivering the drug to the distal ileum, reduced serum Gd-IgA1 by approximately 18 percent and IgA-IgG immune complexes by approximately 7 percent, decreased proteinuria by approximately 27 percent at 9 months, and attenuated the decline in estimated glomerular filtration rate, with sustained renoprotective effects over 2 years and a between-group difference in eGFR of 5.05 mL/min/1.73 m2. However, discontinuation results in re-elevation of serum Gd-IgA1 levels accompanied by recurrence of proteinuria, and long-term efficacy remains to be established. Following accelerated approval by the U.S. FDA in 2021, Nefecon received full approval in December 2023 and has subsequently been approved in Europe and several Asian countries.

The most striking results have come from therapies aimed at later stages of B-cell differentiation. Rituximab effectively depleted peripheral CD20-positive B cells but produced no significant improvements in serum Gd-IgA1 levels, proteinuria, or kidney function after 1 year, suggesting that CD20-negative differentiated plasma cells play a pivotal role. Atacicept, a TACI-Fc fusion protein inhibiting both APRIL and BAFF, reduced serum Gd-IgA1 levels by approximately 60 percent at week 24, sustained through week 72, with an approximately 50 percent reduction in proteinuria and preservation of kidney function. Povetacicept, another dual inhibitor, demonstrated a 77 percent reduction in serum Gd-IgA1 at week 48 with a 64 percent reduction in proteinuria and improvement or resolution of hematuria in approximately 90 percent of patients. Sibeprenlimab, an anti-APRIL monoclonal antibody, reduced serum Gd-IgA1 by approximately 65 percent at 3 months and achieved up to a 62.0 percent reduction in proteinuria at 12 months, while zigakibart produced a 74 percent reduction in serum Gd-IgA1 with a 60 percent reduction in proteinuria at 100 weeks. In contrast, belimumab, an anti-BAFF antibody, has not demonstrated clear clinical efficacy, indicating that APRIL rather than BAFF may play the central pathogenic role. Felzartamab, an anti-CD38 monoclonal antibody aiming to eliminate pathogenic antibody-secreting cells, reduced serum Gd-IgA1 levels and proteinuria by up to 44.8 percent at 9 months with the effect maintained at 24 months, and rilzabrutinib, a Bruton’s tyrosine kinase inhibitor, is currently being evaluated in clinical trials.

Yet the review also confronts an unresolved paradox: not all Gd-IgA1 is pathogenic. Some relatives of patients with familial IgA nephropathy have increased serum Gd-IgA1 levels without developing the disease, and in mice with B cell-specific c1galt1 deletion, markedly elevated serum Gd-IgA1 did not increase glomerular IgA deposition, whereas mucosa-derived IgA1 from patients showed greater mesangial deposition irrespective of its Gd-IgA1 content. An experimental study of anti-APRIL therapy revealed that proteinuria decreased in parallel with improvement in IgA glycosylation during treatment but was maintained even after abnormal glycosylation re-emerged following discontinuation. The CD89-CD71-TGase2 axis has been proposed to promote mesangial deposition, but because the transferrin receptor CD71 is expressed on many cell types, its expression alone cannot explain the selective mesangial deposition. The review authors recently discovered IgA-type anti-mesangial cell autoantibodies, IgA-MESCA, in gddY mice and patients, identifying beta2-spectrin and CBX3 as target autoantigens whose aberrant cell-surface expression appears restricted to mesangial cells. These autoantibodies are detected with high specificity in approximately half of patients, possess the characteristics of Gd-IgA1, and bind to autoantigens presented on the mesangial cell surface, potentially explaining why only a subset of circulating Gd-IgA1 selectively deposits in the mesangium. CBX3-recognizing IgA autoantibodies exhibit cross-reactivity with specific oral bacterial antigens, suggesting induction through molecular mimicry following mucosal infections. Identifying these pathogenic fractions may provide useful biomarkers and facilitate precision therapies, particularly given the challenges in developing standardized assays for anti-Gd-IgA1 autoantibodies due to the heterogeneity of O-glycosylation patterns.

Subject of Research: Immunology

Article Title: Gd-IgA1-targeting therapy in IgA nephropathy ~what is pathogenic Gd-IgA1?~

Article References: Mori, K., Nihei, Y., & Suzuki, Y. (2026). Gd-IgA1-targeting therapy in IgA nephropathy ~what is pathogenic Gd-IgA1?~. Frontiers in Nephrology, 6, Article 1977707. https://doi.org/10.3389/fneph.2026.1977707

Image Credits: AI Generated

DOI: 10.3389/fneph.2026.1977707

Keywords: IgA nephropathy, Gd-IgA1, kidney disease, APRIL, BAFF, B cells, mucosal immunity, Nefecon, autoantibodies, Gd-IgA1-targeting, therapy, nephropathy

At birth, both the innate and adaptive arms of immunity are functionally incomplete. Newborns depend heavily on maternal antibodies transferred across the placenta for passive protection, and this shield decays within months: estimated durations of maternal antibody protection are roughly 3.3 months for measles, 2.7 months for mumps, 3.9 months for rubella, and 3.4 months for varicella. Neonates can mount adaptive responses, but their capacity to generate long-lasting immunity is limited by underdeveloped germinal centers, low expression of B-cell co-receptors such as CD21, CD40, CD80, and CD86, impaired Th1 cytokine secretion, and reduced B-cell receptor signaling strength. The review emphasizes that this is not simple deficiency. The neonatal immune system operates in a tolerogenic mode, likely to prevent immunopathological damage as the infant transitions from a semi-allogeneic, sterile uterine environment into a microbe-rich world, even at the cost of vulnerability to uncontrolled pathogen proliferation.

The innate immune system, the first line of defense, is active from birth and responds within minutes to hours, but its cellular players mature on very different schedules. Neutrophils appear in fetal circulation by the end of the first trimester and surge before delivery, yet neonatal neutrophils show weak inflammatory responses, a deficit most pronounced in premature infants. Monocytes and macrophages in newborns exhibit diminished signaling and cytokine responses compared with adults, reaching normal levels within days. Crucially, the review highlights the newborn microbiome as the first teacher of the developing immune system: gut microbes induce interleukin-17 production by group 3 innate lymphoid cells, which drives granulocyte colony-stimulating factor release and neutrophil production through a Toll-like receptor 4 and MyD88-dependent pathway, maintaining systemic immune vigilance against infection.

Dendritic cells, the sentinels that bridge innate and adaptive immunity, tell a similarly staged story. Plasmacytoid dendritic cells, the body’s type I interferon factories against viruses, constitute 53 percent of the dendritic cell pool in infants, the lowest total dendritic cell proportion of any age group. Although preterm infants possess adult-like levels of TLR7 and TLR9 on these cells, they secrete low amounts of interferon-alpha and beta, leaving antiviral innate immunity ineffective relative to adults. A progressive increase in conventional dendritic cell subsets occurs during the transition from infancy to childhood, suggesting major immune remodeling early in life. In older adults, the dominant subset is cDC2 at 49 percent, while cDC1 cells expand preferentially in adulthood, possibly compensating for the age-related decline in CD8-positive T cells. Lower plasmacytoid dendritic cell proportions in healthy older people may partly explain their reduced capacity to fight viral infections.

Natural killer cells and other innate lymphoid populations undergo their own lifelong remodeling. Newborn natural killer cells have reduced cytolytic function, blunted sensitivity to interleukin-2 and interleukin-15, and lower interferon-gamma secretion, yet still provide some antiviral protection. During pregnancy, maternal peripheral natural killer cells migrate to the decidua and differentiate into non-cytotoxic cells with enhanced secretory activity, producing interferon-gamma, vascular endothelial growth factor, and placental growth factor that are critical for immune tolerance, angiogenesis, and fetal development, though their hyperactivation can trigger spontaneous abortion. With age, natural killer cells shift toward a mature CD56dimCD16-positive phenotype but become dysfunctional in cytotoxicity, degranulation, and cytokine secretion, weakening the elimination of senescent and malignant cells. Strikingly, single-cell RNA sequencing of three centenarian cohorts revealed increased peripheral natural killer cell frequencies in these exceptionally long-lived individuals, alongside reduced CD4-positive T and B cell counts.

That centenarian signature has crystallized into one of the review’s central themes: cytotoxic immunity as a marker of healthy aging. A bioinformatic algorithm developed to identify immune populations associated with longevity found that natural killer cells, CD8-positive T cells, and gamma-delta T cells correlate positively with extended lifespan, whereas inflammatory-lineage populations such as CD4-positive T cells, B cells, and dendritic cells show negative associations. Centenarian neutrophils display phagocytic and chemotactic activities comparable to those of young adults, with low superoxide anion levels and preserved glutathione, while frail middle-aged subjects show the worst profiles. Reduced complement C3 and C4 levels in centenarians contrast with the elevated levels seen in older adults at risk of metabolic syndrome and cardiovascular disease, and caloric restriction has been shown to downregulate the C3a/C3 ratio, attenuating age-related inflammation. Maintaining cytotoxic phenotypes and redox balance, the authors suggest, may be exploitable clinically to blunt immunosenescence.

The adaptive arm follows an equally dramatic arc. T lymphocytes mature in the thymus from seven to eight weeks of gestation and populate the periphery by weeks twelve to thirteen, but thymic involution drives a progressive loss of naive T cells that accelerates after age sixty. Newborns carry only about 1 percent antigen-educated T cells; in adults over sixty, that figure reaches 65 percent. The T cell receptor repertoire narrows with age, CD28 expression is lost from more than half of CD8-positive T cells, and transcriptional reprogramming pushes aging T cells toward a Th2 polarization associated with dysregulated B cell responses and reduced antibody neutralizing capacity after influenza vaccination, a failure that contributes to influenza deaths in 70 to 85 percent of elderly cases. B cells, meanwhile, peak in the first year of life at around six months before gradually declining, and in old age naive B cells are replaced by quiescent memory cells with diminished affinity maturation and class switching.

Perhaps the most conceptually provocative section concerns immunological memory itself. Long considered the exclusive property of adaptive immunity, memory-like responses have now been demonstrated in innate cells, a phenomenon termed trained immunity. Monocytes, macrophages, natural killer cells, and even bone marrow progenitors exposed to stimuli such as beta-glucan or the Bacillus Calmette-Guerin vaccine undergo epigenetic and metabolic reprogramming that confers enhanced, non-antigen-specific protection against unrelated pathogens for months. In murine models, BCG vaccination at birth improved survival in neonatal sepsis with profound remodeling of monocyte and neutrophil subsets, though some pattern recognition receptor agonists failed to protect neonatal mice against Leptospira, underscoring the risks of immunostimulation in early life. In adults over fifty in Guinea-Bissau, BCG vaccination elevated interferon-gamma and pro-inflammatory cytokine responses two months later, and some reports suggest it can reduce circulating inflammatory markers of inflammaging, although recent large trials found no boost to influenza vaccine responses and even flagged aggravation of cardiac arrhythmias as a concern.

The demographic stakes are considerable. The World Health Organization estimates that people over sixty numbered 1.2 billion in 2025 and will reach 2 billion by 2050, with 80 percent living in developing countries, while the European Union’s elderly share is projected to grow from 6.0 percent in 2021 to 14.6 percent by 2100. Immunosenescence, driven by thymic involution, naive cell depletion, inverted CD4/CD8 ratios, gut microbiota shifts that increase intestinal permeability, and the accumulation of senescent cells secreting interleukin-6, tumor necrosis factor-alpha, and interleukin-1 beta, raises vulnerability to infections, cancer, autoimmune disease, and neurodegeneration. Yet the aging immune system paradoxically resembles the newborn’s, with weakened antimicrobial activity and compromised adaptive responses at both ends of life. The Bucharest team argues that mapping these stage-specific mechanisms, from the SOX4-positive naive T cells and interferon-gamma that compensate for infant vulnerability to the cytotoxic dominance that defines centenarian immunity, provides the mechanistic foundation for age-adapted vaccines and immunotherapies capable of restoring immune function in the frail and extending healthy lifespan for everyone else.

Subject of Research: Immune system development across the human lifespan, from neonatal immaturity to immunosenescence and centenarian longevity

Article Title: Immune system ontogeny—a subtle evolution to perfection

Article References: Munteanu, A. N., Surcel, M., Dobre, E. G., Constantin, C., & Neagu, M. (2026). Immune system ontogeny—a subtle evolution to perfection. Frontiers in Aging, 7, Article 1872955. https://doi.org/10.3389/fragi.2026.1872955

Image Credits: AI Generated

DOI: 10.3389/fragi.2026.1872955

Keywords: immunosenescence, inflammaging, trained immunity, neonatal immunity, centenarians, natural killer cells, dendritic cells, T cells, B cells, immunological memory, complement system, BCG vaccine

Immunosenescence, the term researchers use for the structural and functional reorganization of immunity over a lifetime, is closely tied to increased vulnerability to infections, weaker vaccine responses, and a heavier burden of chronic disease. While flow cytometric profiling of blood lymphocyte subsets has become a standard tool for characterizing this process, systematic age-related data on natural killer cell subsets and B cell subsets in healthy Chinese adults have remained scarce. Quantitative trends for CD57 and TEMRA cells, widely accepted markers of terminal T cell differentiation, have also been incompletely described in this population. The new study was designed to fill that gap with two complementary 12-color flow cytometry panels applied across a broad age range.

The researchers prospectively enrolled 146 healthy adults attending the hospital’s annual health examination center between 2023 and 2024. Panel 1 included 103 participants aged 20 to 82 years, while Panel 2 included 43 participants aged 25 to 92 years, deliberately enriched for older individuals to strengthen statistical power at the upper end of the age spectrum. Eligibility required no clinically significant abnormalities on routine examination, and the team excluded anyone with autoimmune disease, chronic infections including HIV, hepatitis B, or hepatitis C, hematological disorders, recent immunosuppressive treatment, acute infection within the preceding four weeks, pregnancy, or evidence of malignancy or severe organ dysfunction.

Panel 1 was a single-tube 12-color assay that simultaneously covered T cells, including CD57 expression, the three-way classification of NK cells by CD56 and CD16 intensity, and the four-way classification of B cells by IgD and CD27. Panel 2 was a dual-tube 12-color assay focused on detailed T cell differentiation, incorporating CD45RA and CD62L to resolve naive, central memory, effector memory, and TEMRA subsets, along with CD28, CD31, CD38, and HLA-DR. At least 100,000 lymphocyte events were acquired per tube on a BD LSRFortessa instrument. Statistical analysis employed Spearman rank correlation, Kruskal-Wallis testing, and Mann-Whitney U tests, with multivariate models controlling for sex.

The strongest age-related signals emerged in the CD8-positive T cell compartment. TEMRA accumulation showed a correlation coefficient of +0.532, CD28 loss reached -0.552, and naive cell depletion reached -0.534, all with p values below 0.001. Together these three changes form a coherent triad representing the hallmarks of replicative senescence in CD8 T cells, painting a picture of progressive, co-stimulation-independent terminal differentiation that dominates this compartment in older individuals. Activation and proliferation markers reinforced the pattern: CD8 cells expressing HLA-DR, CD38 together with HLA-DR, and Ki67 all rose significantly with age, indicating that despite their differentiated phenotype, CD8 T cells in older adults remain in a state of chronic activation.

In the CD4 compartment, two significant age-related changes stood out. CD4-positive CD31-positive cells, which serve as a marker of recent thymic emigrants, declined with age at a correlation of -0.361, consistent with thymic involution progressively curtailing the output of new naive T cells. CD4-positive naive cells also showed a significant decline at -0.303. In Panel 1, the two strongest correlations were both CD57-related: CD4-positive CD57-positive cells rose at +0.421 and CD8-positive CD57-positive cells at +0.338, both highly significant, reflecting progressive accumulation of terminally differentiated T cells across both major subsets. When all 146 participants were pooled for shared markers, both CD4-positive and CD8-positive PD-1 expression became significantly positive, suggesting that exhaustion-like checkpoint upregulation accompanies terminal differentiation as a co-occurring feature of immune aging.

The NK cell findings revealed a more nuanced picture. Total NK cell frequency increased with age, yet within that expanding pool the CD56-high CD16-negative regulatory subset contracted significantly, while the cytotoxic CD56-dim CD16-positive fraction showed no significant proportional change. NK cell PD-1 expression also rose with age, a less commonly reported observation suggesting that NK cells, like T cells, may undergo progressive phenotypic exhaustion. In segmented analysis of the combined dataset, the atypical CD56-negative CD16-positive subset showed no significant overall age correlation but became significantly positively associated with age in participants aged 65 and above, reaching a correlation of +0.482. The researchers caution that the formal slope-change test did not reach significance, so this pattern is best described as a late-life tendency requiring replication rather than a confirmed threshold effect.

B cell aging followed a different timeline. In Panel 1, total B cell frequency was stable across the age range, and among the four IgD/CD27 subsets only the IgD-positive CD27-positive marginal zone-like population showed a significant decline at -0.257. This subset represents antigen-experienced but unswitched B cells, and its contraction may reflect reduced T-independent responses with aging. The more dramatic changes emerged in Panel 2, where total B cell frequency declined significantly at -0.381 and switched memory B cells contracted at -0.379. That these changes appeared in an older-enriched cohort with a median age of 70 but not in the broader Panel 1 sample suggests that substantial B cell contraction may be a relatively late phenomenon, becoming apparent mainly in the oldest age ranges.

Sex was a meaningful source of variation throughout the study. Women tended to have higher CD8-positive fractions and lower CD4-to-CD8 ratios than men of the same age, a pattern consistent with established sex differences in immune aging. Both panels showed higher CD31-positive fractions in women, consistent with greater thymic output or slower naive T cell attrition. Men had higher NK frequency in Panel 2. Critically, however, multivariate analysis showed that sex did not explain the primary age effects; all ten significant age correlations in Panel 1 survived adjustment for sex, and the three core CD8 markers remained strongly significant regardless. The researchers note that the male-heavy composition of Panel 1, at 83.5 percent, introduces some interpretive caution and encourage sex-stratified reporting when these data are used as clinical reference ranges.

To integrate the multidimensional age signal into a single summary measure, the team constructed an Immunological Composite Score from nine parameters showing consistent, sex-independent age associations across both panels. Each parameter was z-scored and combined with directional signs aligned to the age correlation direction. Across all 146 participants, the composite score correlated strongly with chronological age at +0.575, and Kruskal-Wallis testing demonstrated highly significant group separation between young, middle-aged, and older cohorts. The older group differed significantly from both the young and middle-aged groups, while the young and middle-aged groups did not differ significantly from each other. The authors emphasize that the score is presented as a proof-of-concept instrument, derived from and validated in the same dataset, and that external prospective validation in an independent cohort with longitudinal follow-up and clinical endpoints such as infection susceptibility or vaccine immunogenicity is required before any clinical application.

Subject of Research: Age-related changes in T cell, NK cell, and B cell subsets measured by multicolor flow cytometry in healthy Chinese adults

Article Title: Age-associated remodeling of NK cell subsets, B cell subsets, and T cell surface markers in peripheral blood of healthy Chinese adults: a prospective multicolor flow cytometry study

Article References: Zheng, L., Cao, W., Wang, Y., Xu, T., Wang, F., Zhang, L., Liu, X., & Li, T. (2026). Age-associated remodeling of NK cell subsets, B cell subsets, and T cell surface markers in peripheral blood of healthy Chinese adults: a prospective multicolor flow cytometry study. Frontiers in Aging, 7, Article 1847033. https://doi.org/10.3389/fragi.2026.1847033

Image Credits: AI Generated

DOI: 10.3389/fragi.2026.1847033

Keywords: immunosenescence, flow cytometry, T cells, NK cells, B cells, TEMRA, CD57, PD-1, aging, healthy Chinese adults, Peking Union Medical College Hospital, immune aging

The clinical backdrop to the finding is one of the most tantalizing opportunities in modern rheumatology. Anticitrullinated protein antibodies, often abbreviated ACPA, can be detected in the blood of at-risk individuals long before joints become inflamed, and their presence defines a preclinical stage of the disease. Yet only a fraction of ACPA-positive people progress to full-blown rheumatoid arthritis, and clinicians currently have no reliable way to tell who will convert and who will not. That uncertainty has frustrated prevention trials, including earlier attempts at B-cell-directed therapy in the preclinical phase, because the mechanisms that push an at-risk person over the threshold into clinical disease have remained poorly understood. The new study tackles that gap head-on by comparing the B cell landscapes of people who converted to clinical rheumatoid arthritis with those of ACPA-positive individuals who did not, alongside healthy ACPA-negative controls.

Using single-cell RNA sequencing paired with B cell receptor sequencing, the researchers profiled peripheral blood B cells from study participants sampled both before disease onset and after clinical rheumatoid arthritis had been diagnosed. The comparison revealed something remarkable: people who converted to clinical disease showed a marked expansion of a specific subset of activated naive B cells marked by the surface proteins CXCR5 and CD69. Naive B cells are normally the fresh recruits of the adaptive immune system, cells that have never yet encountered their antigen and have not undergone the affinity maturation that sharpens antibody specificity during an immune response. The idea that these immature cells should become activated, expanded and functionally dominant in the run-up to an autoimmune disease upends the conventional picture of how autoimmunity ignites.

The transcriptomic fingerprints of these cells were equally striking. Converters’ aNAV cells expressed proinflammatory gene programs alongside a suite of senescence-associated markers, including genes such as CDKN1A, which encodes the cell-cycle inhibitor p21, and other regulators long associated with aged and dysfunctional cells. In other words, these were not simply energized young lymphocytes responding to infection; they resembled senescent cells, locked into a state of chronic inflammatory secretory activity. The team validated this expansion, activation state and senescent-like phenotype in multiple independent preclinical rheumatoid arthritis cohorts, strengthening the case that the phenomenon is not an artifact of a single group of donors. Perhaps most tellingly, aNAV cells were also detectable in the synovium, the inflamed joint tissue where rheumatoid arthritis does its damage, suggesting that these cells are not bystanders in the circulation but participants in the disease process itself.

What were these cells actually doing? Sequencing of their B cell receptors provided a clue. The aNAV cells from converters expressed unmutated, polyreactive IgM receptors, antibodies capable of binding many different targets rather than one specific antigen, and a substantial fraction showed autoreactivity. Polyreactivity is a property usually associated with natural antibodies and with a subset of B cells that escape central tolerance checkpoints during development. In a healthy immune system, B cells bearing self-reactive or broadly reactive receptors are typically silenced or deleted to prevent autoimmunity. The finding that converters’ expanded aNAV population is dominated by such receptors suggests a breakdown in tolerance that occurs not in the bone marrow where B cells are born, but in the periphery, where chronically stimulated naive cells accumulate autoreactive specificities that would normally never see the light of day.

The functional experiments pushed the story further. In vitro, when the researchers stimulated aNAV cells with citrullinated antigens, the protein fragments bearing the citrulline modification that are the principal targets of the autoimmune response in rheumatoid arthritis, the cells did something naive B cells are not supposed to do well: they acted as antigen-presenting cells. The stimulated aNAV cells promoted T cell activation in a manner dependent on human leukocyte antigen molecules, the proteins that display peptide fragments to T cells for inspection. This means the senescent-like B cells are not merely producing questionable antibodies; they are actively recruiting T cells into the autoimmune conversation, potentially bridging the humoral and cellular arms of the disease. Blocking HLA class I and class II molecules in co-culture experiments abrogated this T cell activation, pinpointing antigen presentation as the mechanism.

The researchers also interrogated what drives naive B cells into this senescent-like activated state in the first place. In culture experiments using naive B cells from people with rheumatoid arthritis and from healthy controls, chronic exposure to citrullinated antigens combined with CpG, a synthetic mimic of bacterial DNA that acts as a potent innate immune stimulant through toll-like receptor 9, synergistically pushed the cells toward activation and senescent-like programming. Neither stimulus alone achieved what the combination did. This synergy offers a plausible mechanistic narrative for the preclinical phase of rheumatoid arthritis: citrullinated proteins, generated at sites of inflammation such as the lung or gum tissue where mucosal breaks have been implicated in triggering anticitrullinated antibody responses, together with innate immune signals from microbial stimulation, chronically tickle naive B cells until they adopt a dysfunctional, inflammatory, self-reactive identity that primes the system for clinical disease.

The implications for prevention are considerable. Because the aNAV expansion was observed before disease onset and distinguished converters from nonconverters, these cells could serve as a biomarker, a way of identifying which ACPA-positive individuals are truly on the path to clinical rheumatoid arthritis and might benefit most from early intervention. More ambitiously, the cells themselves represent a potential therapeutic target. If senescent-like aNAV cells are genuine contributors to disease progression rather than passive correlates, strategies aimed at depleting them, interrupting their antigen-presentation function, or reversing their senescent programming could intercept the disease before joints are ever damaged. The study’s authors are careful to frame these cells as potential contributors and therapeutic targets for prevention, and the distinction matters: demonstrating correlation across cohorts and mechanism in vitro is a crucial step, but clinical trials will be needed to show that targeting aNAV biology can actually prevent disease.

The work also resonates with a broader theme in immunology, the growing recognition that B cell senescence shapes both aging and autoimmune disease. Recent studies have shown that bacterial induction of B cell senescence drives age-related changes in the gut microbiota, that B cell senescence alters oral microbial communities, and that chronic B cell receptor signaling can push anergic B cells toward age-associated B cell states in autoimmunity. The new findings slot rheumatoid arthritis squarely into this emerging framework, portraying the preclinical phase as a period in which chronic antigenic and innate stimulation ages a subset of naive B cells prematurely, endowing them with the tools, autoreactive receptors, inflammatory gene programs and antigen-presenting capacity, to help ignite systemic autoimmunity. With the single-cell datasets and analysis code publicly deposited, the study offers the research community a detailed map of this process, and it reframes a question that has haunted rheumatology for decades: not simply why the immune system attacks the joints, but which cells, in the quiet years before the first swollen knuckle, decide to lead the charge.

Subject of Research: Senescent-like activated naive B cells in the progression from preclinical autoimmunity to clinical rheumatoid arthritis

Article Title: Senescent-like activated naive B cells contribute to progression to clinical rheumatoid arthritis

Article References: Wu, X., Zhang, M., Moon, J.-S., Song, E. K., Abrams, J. C., van Dam, L. S., Sharpe, O., Wang, Z., Feser, M. L., Moss, L., Ho, P. P., Smith, M. H., Donlin, L. T., Buckner, J. H., James, E. A., Firestein, G. S., Okamoto, Y., Lanz, T. V., Meffre, E., … Robinson, W. H. (2026). Senescent-like activated naive B cells contribute to progression to clinical rheumatoid arthritis. Nature Aging, 6(10), 2143-2163. https://doi.org/10.1038/s43587-026-01236-6

Image Credits: AI Generated

DOI: 10.1038/s43587-026-01236-6

Keywords: rheumatoid arthritis, B cells, senescence, autoimmunity, ACPA, single-cell multiomics, antigen presentation, T cells, preclinical disease, immune aging, citrullinated antigens, disease prevention

The finding is significant because IgE sits at the very center of the allergic cascade. Allergen-specific IgE is produced exclusively by B cells, and upon re-exposure to an allergen such as house dust mite, these antibodies arm mast cells and basophils, triggering their degranulation and the clinical symptoms of asthma. At the same time, T helper 2 cells recruited to the airways secrete IL-4, IL-5 and IL-13, cytokines that promote local IgE production, eosinophil accumulation, airway hyperresponsiveness and mucus hypersecretion. While the extracellular signals that push B cells toward IgE have been studied extensively, the intrinsic molecular machinery inside B cells that governs this process has remained poorly defined, which is precisely the gap the new work addresses.

The researchers began by asking whether Ssu72 responds to the signals that activate B cells during allergic reactions. In cultured mouse B cells, Ssu72 protein and mRNA levels rose markedly after stimulation with anti-CD40, an antibody that mimics the T cell help B cells receive through CD40 ligation, as well as after combined anti-IgM and anti-CD40 stimulation and exposure to the T helper 2 cytokine IL-4. Crucially, the pattern held in vivo: in a low-dose house dust mite model of allergic asthma, B cells from the spleens of asthmatic mice showed significantly elevated Ssu72 compared with controls, and immunofluorescence imaging revealed heightened Ssu72 expression in B220-positive B cells infiltrating the inflamed lungs. The enzyme, in other words, is switched on exactly where and when the allergic response is being built.

To test whether this upregulation matters functionally, the team generated mice lacking Ssu72 only in B cells by crossing Ssu72-floxed animals with CD19-Cre mice, producing what they call Ssu72-BKO mice. Importantly, baseline B cell development appeared largely intact: total splenic B cell numbers were comparable to wild-type littermates, and with careful gating the major follicular, transitional and marginal zone subsets were unchanged. The knockout mice also mounted normal antigen-specific IgM and IgG responses after immunization with T cell-dependent and T cell-independent antigens, formed normal germinal centers and generated normal plasma cell populations. Ssu72, it seems, is dispensable for general antibody immunity but becomes critical in the specific context of allergic, T helper 2-driven inflammation.

That context-dependence showed itself clearly in the asthma model. After sensitization and challenge with house dust mite extract, Ssu72-BKO mice had visibly less peribronchial and perivascular inflammation on histology, lower inflammation scores, and significantly fewer total cells, eosinophils, T cells and B cells in bronchoalveolar lavage fluid. Immunohistochemistry for B220 and eosinophil cationic protein confirmed reduced B cell and eosinophil infiltration in lung tissue. Most strikingly, serum levels of total and house dust mite-specific IgE and IgG1 were substantially lower in the knockout animals, while HDM-specific IgM, IgG2b and IgG3 were unaffected, indicating that B cell Ssu72 preferentially supports the IgG1 and IgE arms of the allergic antibody response.

Flow cytometry of the mediastinal lymph nodes revealed why. Class switching to IgG1 and IgE normally occurs in germinal centers with help from T follicular helper cells, and in Ssu72-BKO mice both the percentage and number of IgG1-positive B cells, germinal center B cells and T follicular helper cells were significantly reduced after asthma induction. The defect was also cell-intrinsic: when purified B cells from knockout and wild-type mice were stimulated in vitro with LPS plus IL-4, the Ssu72-deficient cells showed markedly fewer IgG1-positive cells at days three and six, fewer intracellular IgE-positive cells at day six, and lower secreted IgG1 and IgE, while IgM production was unaffected. The knockout B cells also proliferated less, expressed less Ki67, survived less well by Annexin V and propidium iodide staining, and showed blunted early activation markers CD69 and CD86.

The study also uncovered a second, mechanistically distinct route by which Ssu72 shapes IgE: the regulation of CD23, the low-affinity IgE receptor. Membrane-bound CD23 on B cells normally restrains IgE synthesis, whereas its cleaved soluble form, sCD23, enhances it. Ssu72-BKO mice produced significantly less sCD23 during house dust mite asthma while retaining higher levels of membrane CD23 on their lymph node B cells. The team traced this to reduced induction of ADAM10, the established sheddase that clips CD23 from the cell surface, and reduced expression of MMP9, a matrix metalloproteinase previously implicated in LPS-driven CD23 cleavage. Consistent with a conserved mechanism, an analysis of public RNA sequencing data from activated human B cells revealed a positive correlation between Ssu72 and MMP9 expression, suggesting the pathway may operate in human allergy as well.

Delving deeper into signaling, the researchers found that Ssu72-deficient B cells had reduced phosphorylation of S6K and S6, canonical readouts of mTORC1 activity, alongside sharply increased phosphorylation of AMPKα at Thr172, the activating modification of the cellular energy sensor AMPK. Because AMPK negatively regulates mTORC1, and mTORC1 drives the protein synthesis and anabolic growth that class-switched B cells need to proliferate and secrete antibody, this imbalance offers a coherent explanation for the defective IgG1 and IgE responses. Co-immunoprecipitation experiments in transfected HEK293T cells and in the human Ramos B cell line demonstrated a physical interaction between Ssu72 and AMPKα, raising the possibility that Ssu72 directly dephosphorylates AMPKα, although the authors note that direct phosphatase assays and catalytically inactive Ssu72 mutants will be needed to confirm AMPKα as a true substrate.

Perhaps the most clinically suggestive result came from adoptive transfer experiments. When B cells from wild-type or Ssu72-deficient donors were transferred into B cell-deficient μMT mice that had already been sensitized to house dust mite, and the recipients were then challenged, the mice receiving Ssu72-deficient B cells developed less lung inflammation, fewer airway eosinophils, T cells and B cells, and lower serum IgE. This shows that Ssu72 matters not only during the sensitization phase, when IgE-switched B cells are generated, but also during the effector phase, when re-exposure to allergen triggers disease. The knockout B cells additionally displayed reduced MHC class II upregulation in lymph nodes and lungs, and the mice showed fewer IL-4- and IL-13-producing CD4-positive T cells in both compartments, along with lower IL-4 in bronchoalveolar lavage fluid and serum, implying that Ssu72-expressing B cells help sustain the T helper 2 dialogue through antigen presentation.

Taken together, the study positions Ssu72 as a context-dependent, B cell-intrinsic checkpoint that licenses class switching to IgG1 and IgE, promotes CD23 shedding through ADAM10 and MMP9, and tunes the AMPK-mTORC1 metabolic axis. Because general humoral immunity was preserved in the knockout mice, the authors argue that selectively targeting Ssu72 in B cells could dampen allergic airway inflammation without broadly compromising the antibody defenses a patient needs against infection. Much remains to be worked out, including how Ssu72 controls ADAM10 and MMP9 expression and how the AMPK and CD23-shedding pathways intersect. But for a disease in which IgE remains a prime therapeutic target, an intracellular enzyme that quietly orchestrates its production offers an enticing new lead, and one that the field will now be eager to pursue from mouse airways toward human clinics.

Subject of Research: The role of the B cell-intrinsic phosphatase Ssu72 in regulating IgE production and allergic airway inflammation

Article Title: B cell-intrinsic Ssu72 phosphatase is a key regulator of allergic asthma

Article References: Koo, S.-Y., Wang, N., Kim, M.-H., Lee, S., Kim, T. J., & Lee, C.-W. (2026). B cell-intrinsic Ssu72 phosphatase is a key regulator of allergic asthma. Experimental & Molecular Medicine. https://doi.org/10.1038/s12276-026-01859-0

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01859-0

Keywords: Ssu72 phosphatase, B cells, allergic asthma, IgE, class switch recombination, CD23 shedding, ADAM10, MMP9, AMPK, mTORC1, T helper 2 cytokines, house dust mite

The study, led by Daniel Arroyo-Sánchez and Oscar Cabrera-Marante of the Immunology Department at Hospital Universitario 12 de Octubre and published in the Journal of Translational Medicine, set out to answer a deceptively simple question: what happens to the B cells of CVID patients when they are pushed to produce antibodies under controlled laboratory conditions? To find out, the researchers isolated peripheral blood mononuclear cells, the mixed population of immune cells circulating in the blood, from 20 patients with CVID and from healthy donors. These cells were then cultured in the laboratory with a carefully chosen cocktail of stimuli: interleukin-2, a cytokine that supports lymphocyte survival and proliferation, and R848, a synthetic compound that activates Toll-like receptors, the molecular sensors that normally alert B cells to microbial invasion and drive them toward antibody-secreting states.

The choice of stimulation is scientifically significant. Toll-like receptor signaling has become an increasingly important focus in immunodeficiency research because it mimics a key pathway used during natural infection and, notably, during vaccination. Recent clinical observations had shown that some CVID patients mount partial responses to mRNA vaccines, hinting that a residue of functional capacity might survive within their B-cell compartment. By combining IL-2 with R848, the team created conditions designed to coax out whatever antibody-producing potential the patients’ cells still possessed, and then to measure precisely how far that potential could carry them.

The results, tracked over a ten-day culture period, revealed a striking temporal pattern. In cultures from healthy controls, antibodies remained readily detectable in the culture supernatants throughout the observation window, a sign that the cells had successfully differentiated into antibody-secreting cells and sustained their output. In cultures from CVID patients, by contrast, the ability to sustain antibody production collapsed. By day 10, the patients’ cultures had failed to maintain antibody secretion, and the cellular composition of those cultures told its own story: a predominance of IgD-CD27- B cells, a subset that lacks the classical markers of activated memory cells and is generally associated with a less mature, less responsive state.

Crucially, the defect was not a simple absence of responsive cells. On day 6 of culture, the proportion of memory B cells in the patients’ cultures was comparable to that seen in healthy controls. This timing matters enormously for interpretation. It suggests that CVID B cells can initially be pushed toward a memory-like phenotype when stimulated through Toll-like receptors in the presence of IL-2, but that this apparent activation cannot be consolidated into durable antibody output. The failure, in other words, appears to lie in the later stages of the differentiation program, in the transition from an activated, memory-like state to a fully functional antibody-secreting plasma cell, rather than in the earliest steps of B-cell activation.

To probe the molecular roots of that failure, the researchers turned to transcriptomic analysis, sequencing the gene expression profiles of the cultured cells. The comparison between patients and healthy controls uncovered a coherent pattern of dysregulation. Genes related to antibody production were expressed at lower levels in the patients’ cells, consistent with the observed collapse in antibody secretion. Genes involved in adhesion and in proinflammatory signaling were also downregulated, pointing to a broader failure of the activated B cell to adopt the full behavioral repertoire of a responding immune cell, including the physical interactions with other immune cells that normally support germinal-center-like reactions in the culture dish.

Perhaps most intriguingly, the patients’ cells showed increased expression of genes associated with immune inhibitory responses. This shift toward an inhibitory program provides a mechanistic explanation for the paradox that has long defined CVID: B cells that are present, sometimes numerous, and capable of at least partial activation, yet chronically unable to deliver protective antibodies. If the cells are actively ramping up inhibitory pathways in response to stimulation, then the defect may not be a passive inability to respond but an active regulatory brake, one that engages precisely when the cells should be committing to antibody production.

The analysis of soluble factors in the culture supernatants reinforced this picture. Compared with healthy controls, the patients’ cultures contained lower concentrations of APRIL, a cytokine that plays a well-established role in supporting B-cell survival and the differentiation of antibody-secreting cells, and lower levels of interferon-alpha, an antiviral cytokine with important immunoregulatory functions. At the same time, the patients’ supernatants showed higher concentrations of BTLA, an inhibitory receptor of the CD28 family that delivers dampening signals to lymphocytes. The combination is telling: the patients’ cultures were simultaneously deprived of positive differentiation signals and enriched for inhibitory ones, a molecular environment stacked against sustained antibody output.

Taken together, the study’s findings sketch a coherent model of B-cell dysfunction in CVID. When stimulated through Toll-like receptors, the cells of these patients can begin the journey toward activation and memory differentiation, but they cannot sustain it. Their gene expression programs drift away from antibody production, adhesion, and inflammation and toward immune inhibition, while their soluble environment loses the supportive cytokines that healthy cultures provide. The researchers suggest that these insights into functional impairment after Toll-like receptor stimulation may be directly relevant to the B-cell dysfunction observed in patients with CVID, and they may help explain why some patients show only partial responses to vaccines that depend heavily on this signaling pathway.

The work also carries practical implications for the future. An in vitro assay that reliably distinguishes the functional profile of CVID B cells from healthy ones could, with further validation, help stratify patients, identify those with residual responsiveness, and guide more individualized approaches to immunoglobulin replacement and vaccination strategies. The study was approved by the Institutional Ethics Committee of Hospital Universitario 12 de Octubre and conducted with written informed consent from all participants, whose willingness to donate blood samples the authors explicitly acknowledged. Funded through Spanish COVID-19 research projects and supported by the genomic analysis group of the Spanish National Cancer Research Centre, the research exemplifies how translational immunology can turn a bedside mystery, why vaccinated patients remain vulnerable, into a bench-side mechanism, one inhibitory signal at a time.

Subject of Research: B-cell functional impairment in common variable immunodeficiency assessed by in vitro Toll-like receptor stimulation

Article Title: Common variable immunodeficiency: B cells' impairment in an in vitro assay

Article References: Arroyo-Sánchez, D., Chivite-Lacaba, M., González-Cuadrado, C., Almendro-Vázquez, P., Bermejo Olivera, F. J., Andara-Cordero, L. A., Garcinuño, S., Velasco-Sidro, M., Nieto-López, C., Alfocea Molina, Á., Cantonad Ruigómez, C., Pascual Palacios, L., Pleguezuelo-Garrote, D. E., Paz-Artal, E., & Cabrera-Marante, O. (2026). Common variable immunodeficiency: B cells' impairment in an in vitro assay. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08821-8

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08821-8

Keywords: common variable immunodeficiency, B cells, antibody production, Toll-like receptor, R848, interleukin-2, transcriptomics, ELISPOT, flow cytometry, APRIL, BTLA, primary immunodeficiency

The research, led by Wei Hang of Cardiff University together with colleagues at Fujian Provincial Hospital, the Fujian Center for Disease Control and Prevention and partner institutions in China, applied single-cell RNA sequencing to characterize the peripheral immune landscape associated with post-COVID pulmonary fibrosis. Rather than measuring average gene expression across bulk blood samples, single-cell transcriptomics profiles each individual cell, allowing researchers to detect shifts in the composition and functional state of rare immune subsets that would otherwise be invisible. The team integrated data from 115 samples drawn across multiple cohorts, combining publicly available acute-phase COVID-19 datasets with an in-house cohort recruited in Fujian province.

The design of the study reflects the central challenge of fibrosis research: the scar tissue itself is buried deep in the lung, inaccessible to routine sampling. The investigators therefore worked backwards from outcome. Public acute-phase datasets were stratified by an estimated fibrosis risk score, yielding a high-risk group of 50 patients and a low-risk group of 52. These were complemented by the Fujian cohort, in which 13 patients were sampled at the two-week post-discharge timepoint; seven of them had CT-confirmed pulmonary fibrosis while six did not. By comparing immune profiles across these strata, the researchers sought peripheral signatures that track with fibrotic risk even before structural damage becomes radiologically obvious.

The headline finding is a pronounced dysregulation of the B cell compartment in patients judged to be at higher fibrosis risk. Naive B cells, the resting, uncommitted lymphocytes that have not yet encountered antigen, were depleted in the high-risk groups. In their place, the researchers observed an expansion of activated B cells, plasmablasts and plasma cells, the antibody-secreting arm of the B lineage. This shift from a naive, quiescent pool toward a terminally differentiated, secretory population suggests that in patients prone to fibrosis, the humoral immune response remains locked in an activated state long after the acute viral challenge has passed.

Crucially, the different expanded subsets carried distinct functional imprints in their gene expression. Plasma cells from high-risk patients showed enrichment of transforming growth factor beta signaling, a pathway long implicated in driving fibroblasts to deposit scar-forming matrix, together with collagen metabolism and extracellular matrix remodeling programs. Plasmablasts, by contrast, were enriched for inflammasome-related genes, tumor necrosis factor signaling and angiogenesis pathways. In other words, the antibody-producing cells of high-risk patients were not merely numerous; they were transcriptionally wired toward the very biological processes, matrix deposition, inflammatory amplification and new blood vessel formation, that characterize the fibrotic niche in lung tissue.

The study also identified a potentially pathogenic B cell state marked by expression of FCRL5, an Fc receptor-like molecule associated with exhausted B cells. Elevated proportions of these FCRL5-positive exhausted B cells, alongside raised fractions of plasmablasts, were each statistically associated with increased mortality, as were reduced proportions of naive and memory B cells, with all of these associations reaching significance at p less than 0.05. The convergence of subset imbalance and survival outcome strengthens the argument that peripheral B cell architecture is not a passive bystander in post-COVID disease but a measurable correlate of clinical deterioration.

Clinically, the fibrosis risk stratification itself carried prognostic weight. Patients assigned to the high fibrosis risk group showed significantly worse short-term survival, with the difference reaching p less than 0.001. This means the grouping used to organize the transcriptomic analysis was not an arbitrary computational construct but a discriminator that separated patients by outcome. If the B cell features underlying that grouping can be reproduced in prospective cohorts, they could form the basis of a peripheral immune profiling strategy, a blood test capable of flagging which COVID-19 survivors warrant intensified radiological follow-up or early anti-fibrotic intervention.

The technical approach deserves attention in its own right. Integrating single-cell data across multiple cohorts is a nontrivial exercise, because datasets generated in different laboratories, on different platforms and from different patient populations carry systematic batch effects that can masquerade as biological signals. By requiring that B cell signatures replicate across independent public cohorts and an in-house post-discharge cohort with CT-confirmed outcomes, the authors mitigated the risk that their findings reflect artifacts of any single dataset. The two-week post-discharge sampling window in the Fujian cohort is particularly valuable, since it captures the immune system at a point where fibrotic processes are likely to be initiated but not yet fixed.

The findings also reframe the role of B cells in fibrotic disease more broadly. Pulmonary fibrosis research has traditionally centered on fibroblasts, macrophages and epithelial injury, with humoral immunity treated as peripheral to the scarring process. The observation that plasma cells in high-risk patients express coordinated TGF-beta, collagen and matrix remodeling programs suggests that antibody-secreting cells may participate directly in profibrotic signaling, or at minimum serve as circulating sentinels of fibrotic activity occurring in the lung. Either interpretation carries implications: the first points to B cell-directed therapies as potential antifibrotic strategies, while the second supports serial immune monitoring as a surrogate for disease activity.

The authors are careful to frame their results as identifying candidate biological processes rather than validated diagnostic markers. The associations were drawn largely from acute-phase samples stratified by estimated risk, and the post-discharge cohort, while clinically grounded, comprised only 13 patients. Prospective longitudinal studies will be needed to confirm whether B cell dysregulation precedes fibrosis development or accompanies it, and whether the signature retains predictive power in vaccinated populations and in the era of Omicron-lineage variants. Nevertheless, the study provides a concrete, mechanistically annotated set of peripheral immune features, depleted naive and memory B cells, expanded plasmablasts and plasma cells, and FCRL5-positive exhausted B cells, that can be tested directly. For the millions of COVID-19 survivors worldwide who live with uncertainty about their long-term lung health, a simple blood-based indicator of fibrosis risk would represent a meaningful step toward earlier detection and intervention.

Subject of Research: Peripheral B cell dysregulation associated with post-COVID-19 pulmonary fibrosis identified through multi-cohort single-cell RNA sequencing

Article Title: Peripheral B cell dysregulation associated with post-COVID-19 pulmonary fibrosis characterized by multi-cohort single-cell transcriptomics

Article References: Hang, W., Wu, S., Lin, H., Wu, Y., Zhong, W., Fang, J., Wu, J., He, Y., Xiao, Y., Ren, L., Xu, N., Lin, R., Zhou, Y., Li, H., & Li, H. (2026). Peripheral B cell dysregulation associated with post-COVID-19 pulmonary fibrosis characterized by multi-cohort single-cell transcriptomics. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08885-6

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08885-6

Keywords: post-COVID-19, pulmonary fibrosis, B cells, single-cell RNA sequencing, plasmablasts, plasma cells, TGF-beta signaling, extracellular matrix, immune biomarker, FCRL5, COVID-19, transcriptomics