The study, led by Associate Professor Jacques Behmoaras and first author Dr. Harry Park from the Centre of Biomedical Data Science, utilized single-cell RNA sequencing data to map the genetic activity of immune cells across the entire human lifespan. The cohort included individuals aged 19 to 97, with a diverse demographic composition that included a significant number of participants of Asian ethnicity. This large-scale integration of publicly available research datasets allowed the team to create a comprehensive immune atlas, offering a high-resolution view of how the immune system evolves over time. The analysis focused on the transcriptomic profiles of various immune cell types, particularly T cells, which are central to coordinating the body’s defense mechanisms against pathogens.

The researchers discovered that the fundamental machinery responsible for cellular function, specifically the genes involved in the synthesis of RNA and proteins, experiences its most pronounced decline during two specific windows: around age 40 and again after age 60. These periods represent critical inflection points where the immune system undergoes rapid reorganization. Rather than a steady erosion of capacity, the data suggests that the immune system undergoes abrupt changes in gene expression patterns. This nonlinear trajectory implies that the body’s immune resilience is not simply lost bit by bit, but rather that specific functional capacities are compromised at distinct life stages, potentially leaving individuals more vulnerable to specific types of immune dysregulation during these periods.

T cells emerged as the primary drivers of these nonlinear changes. The study found that T cells, a type of white blood cell essential for fighting infections, showed the most significant alterations in gene activity during the first wave around age 40. This early shift likely reflects the central role T cells play in coordinating the immune response and their heightened sensitivity to the initial effects of aging. Interestingly, the specific subtypes of T cells that undergo profound changes at age 40 are different from those that drive the second wave of changes after age 60. This distinction suggests that T cells have specialized roles at different stages of life, and that the aging process affects these specialized functions in a staggered manner.

One of the most significant findings of the study is the identification of sex-specific differences in immune aging trajectories. While both men and women experience the two major waves of immune aging, the specific patterns of gene activity and the types of T cells involved differ between the sexes. These differences may help explain why women are more likely than men to develop autoimmune diseases, such as lupus and rheumatoid arthritis, despite generally living longer. In Singapore alone, more than 600,000 people, or about 11 percent of the population, suffer from autoimmune conditions. The study suggests that the immune system’s response to aging is not uniform, and that sex-specific biological pathways may predispose individuals to different types of immune-related disorders at different stages of life.

Professor Antonio Bertoletti, a co-author of the study and a leader in the Emerging Infectious Diseases Signature Research Programme at Duke-NUS, emphasized the importance of understanding these nonlinear changes. He noted that previous evidence had suggested T cells are among the immune cells most affected by aging, but the new study provides a detailed map of how and when these changes occur. Understanding the specific biological pathways that drive these shifts could help explain why older adults are more susceptible to infections and inflammatory conditions. The findings suggest that interventions aimed at boosting immune function may need to be timed to coincide with these critical windows of vulnerability to be most effective.

To further explore the implications of these findings, the scientists developed artificial intelligence models capable of predicting biological age based on the immune cell data. Biological age is an estimation of the ‘true age’ of the body, which can differ from chronological age. By using these AI models, researchers can identify individuals whose immune systems are aging faster or slower than their peers. This tool could be used to tailor preventive strategies and treatments based on an individual’s biological age and sex, moving away from a one-size-fits-all approach to aging. The ability to predict biological age from immune cell profiles opens up new possibilities for personalized medicine, where treatments can be adjusted to match the specific needs of a patient’s immune system.

The study was conducted in collaboration with several Signature Research Programmes at Duke-NUS, including those in Cardiovascular and Metabolic Disorders, Cancer and Stem Cell Biology, and Emerging Infectious Diseases. Partners from the NUS Yong Loo Lin School of Medicine also contributed to the research. Professor Sheemei Lok, Duke-NUS’ Interim Vice-Dean for Research, highlighted the significance of the findings for the field of aging research. She stated that the study provides a more detailed map of how the human immune system changes across the lifespan, and importantly, how those trajectories differ between men and women. This knowledge is fundamental for developing precise approaches to maintaining health as people grow older, rather than relying on generalized strategies that may not account for individual biological differences.

The research was supported by the National Research Foundation, Singapore, and the National Medical Research Council, underscoring the importance of this work in the context of Singapore’s healthcare landscape. The findings have broad implications for global health, as the patterns of immune aging observed in this diverse cohort are likely to be relevant to other populations. By identifying the specific windows of immune vulnerability and the sex-specific differences in these trajectories, the study provides a foundation for future research into targeted interventions. Understanding the nonlinear nature of immune aging could lead to the development of therapies that are more effective at preventing or treating age-related immune disorders, ultimately improving the quality of life for older adults.

As the global population ages, the need for a deeper understanding of the biological mechanisms underlying age-related diseases becomes increasingly urgent. This study represents a significant step forward in that effort, providing a new perspective on how the immune system changes over time. By revealing the distinct waves of immune aging and the sex-specific differences in these trajectories, the researchers have opened up new avenues for investigation and intervention. The findings suggest that the future of aging research lies in a more nuanced, personalized approach that takes into account the complex, nonlinear dynamics of the immune system. This work not only advances our scientific understanding but also holds promise for improving clinical outcomes for patients suffering from immune-related diseases.

Subject of Research: Nonlinear trajectories of sex-specific immune aging at the single-cell level

Article Title: Immune ageing accelerates around 40 and 60, with key differences between men and women

Article References: Immune ageing accelerates around 40 and 60, with key differences between men and women. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Immune Aging, Single-Cell RNA Sequencing, T Cells, Autoimmune Diseases, Sex-Specific Differences, Biological Age, Genome Activity, Duke-NUS Medical School, Nature Communications, Nonlinear Aging, Personalized Medicine, Immune Atlas

The research team began by examining peripheral blood from healthy human volunteers, stratified into young adults aged 18 to 40 and middle-aged adults aged 41 to 65. When natural killer cells were stimulated in the laboratory with the cytokine interleukin-15, a potent activator of NK cell activity, a striking sex-specific pattern emerged. Cells from middle-aged men expressed significantly lower levels of CD107a, a marker of degranulation that reflects the cell’s ability to release its cytotoxic payload, and produced markedly less interferon-gamma, the signature cytokine that coordinates antiviral and antitumor responses. In contrast, natural killer cells from middle-aged women performed comparably to those from young women across these functional readouts. Enzyme-linked immunosorbent assays of purified CD3-negative CD56-positive cells confirmed that the cytokine secretion deficit in middle-aged men was genuine and not an artifact of intracellular staining.

Surface receptor profiling added further nuance. The investigators measured a panel of receptors known to regulate natural killer cell development and function, including CD150, 2B4, CD84, CD319, NKG2A, NKG2D, CD48, Ly9, Ly108, Tim-3, and CD69. Most of these were unchanged between age groups, but young male donors displayed higher expression of CD48, a ligand involved in activating signals. The authors conclude that reduced cytotoxic function and diminished cytokine production are defining characteristics of natural killer cells in middle-aged men, even in the absence of overt disease.

To dissect the mechanisms behind this human observation, the team turned to a mouse model, comparing 8-week-old young males with 48-week-old middle-aged animals, an age that corresponds roughly to human midlife. Consistent with prior work, the middle-aged mice were substantially heavier, with magnetic resonance imaging revealing elevated fat mass and enlarged epididymal and inguinal white adipose depots. Brown adipose tissue also increased in mass, but its thermogenic browning capacity was significantly diminished. Metabolic cage experiments painted a coherent picture of midlife metabolic decline: oxygen consumption, carbon dioxide production, respiratory exchange ratio, and whole-body energy expenditure all fell significantly, even though spontaneous activity levels were comparable between age groups. Food and water intake were actually reduced, underscoring that the adiposity of middle age reflects a fundamental shift in basal metabolism rather than simple overconsumption.

Flow cytometric analysis across the spleen, bone marrow, liver, peripheral blood, and adipose tissues revealed that natural killer cells were among the most affected immune populations. The relative proportion of NK cells dropped significantly in the spleen and liver, and within adipose tissue the percentage fell in epididymal white adipose tissue, with numbers per gram of tissue reduced across all three fat depots. Maturation, tracked using the classical CD27 and CD11b staging scheme, was also impaired. Middle-aged mice showed an accumulation of immature CD27-positive single-positive cells and a loss of mature CD11b-positive single-positive cells in the spleen and bone marrow, a pattern resembling that previously described in much older animals. In the fat depots, mature subsets were similarly depleted. Notably, the liver appeared relatively spared, suggesting tissue-specific vulnerability. Broader immune profiling using t-distributed stochastic neighbor embedding showed that other lymphocyte populations were largely unchanged, with the notable exception of increased M1 and M2 macrophages in the spleen, reinforcing that natural killer cells represent a particularly sensitive target of the midlife immune environment.

The receptor landscape of natural killer cells shifted in ways that would be expected to blunt surveillance. In the spleen, the inhibitory receptors KLRG1 and TIGIT were downregulated while Ly49A was upregulated, and the activation marker CD69 along with the immature markers CD117 and CD127 were elevated, consistent with a less differentiated, functionally compromised state. Adipose tissue NK cells displayed their own distinctive receptor changes, with broad upregulation of multiple activating and inhibitory receptors in epididymal fat. Survival analysis helped explain the falling cell counts: splenic natural killer cells from middle-aged mice showed increased Annexin V positivity, indicating heightened apoptosis, alongside reduced Ki-67 expression, a marker of proliferation. Proliferation was also reduced in bone marrow, epididymal fat, and brown fat. Single-cell RNA sequencing of splenic and bone marrow NK cells reinforced the functional picture, revealing downregulation of NK cell activation pathways and upregulation of p53-mediated signaling in middle-aged animals.

Function followed form. When splenocytes or bone marrow cells were challenged ex vivo with MHC class I-deficient target cells such as YAC-1 and RMA-S, natural killer cells from middle-aged mice produced significantly less interferon-gamma and expressed less surface CD107a than those from young controls. The deficit extended deep into the adipose tissue microenvironment: NK cells isolated from epididymal, inguinal, and even brown fat depots showed markedly impaired degranulation and cytokine production. Imaging flow cytometry using the neutral lipid dye Bodipy 493/503 provided a possible mechanistic clue. Natural killer cells from middle-aged mice accumulated more intracellular lipid than those from young mice, with the most pronounced lipid burden observed in cells residing in epididymal white adipose tissue. This finding echoes earlier reports that lipid droplet accumulation inside NK cells can compromise their cytotoxic machinery, and it suggests that a lipid-enriched adipose microenvironment may directly poison the antitumor capacity of these lymphocytes.

To separate the effects of aging from those of obesity itself, the researchers fed 8-week-old young male mice a high-fat diet deriving 60 percent of calories from fat for 16 weeks. These diet-induced obese animals, though young, mirrored many of the NK cell defects seen in their middle-aged counterparts. Splenic and bone marrow natural killer cells showed reduced interferon-gamma production and degranulation upon target cell stimulation, and cells within all three adipose depots displayed the same functional impairment. The authors note that NK cell dysfunction was, if anything, more pronounced in the high-fat diet group than in middle-aged mice, likely because the dietary model produced even greater adipose expansion. Together with previous reports that dietary restriction can enhance NK cell function, this experiment supports the interpretation that excess adiposity itself, independent of chronological age, is a major driver of the immune decline observed in midlife.

The study has limitations that the authors acknowledge. The comparison between middle-aged obesity and diet-induced obesity is indirect and cannot fully disentangle the two conditions, and the focus on male participants and male mice, justified by the far more pronounced weight gain and adipogenesis seen in males during middle age, leaves sex-specific differences in female biology largely unexplored. Nevertheless, the implications are considerable. Epidemiological data indicate that middle-aged adults with obesity face a higher mortality risk than expected for their conditions, and the loss of natural killer cell quantity and surveillance documented here offers a plausible immunological mechanism linking midlife weight gain to increased vulnerability against cancer and infections. Because white adipose tissue is the first organ to show age-related transcriptomic changes beginning in middle age, and because longevity-promoting pathways such as sirtuins and forkhead box proteins typically suppress adipogenesis, the study positions the expanding fat depot not merely as a passive energy store but as an active remodeler of systemic immunity. If confirmed in larger and more diverse cohorts, these findings suggest that maintaining metabolic health through the middle decades could help preserve the innate immune defenses that guard the body against malignancy and viral disease well before old age arrives.

Subject of Research: Natural killer cell dysfunction during midlife obesity in humans and mice

Article Title: Natural Killer Cell Dysfunction Is Emerging During Midlife Obesity

Article References: Biao, R., Wang, X., Fu, J., Guo, Y., He, J., & Du, J. (2026). Natural Killer Cell Dysfunction Is Emerging During Midlife Obesity. Aging Cell, 25(9), Article e70707. https://doi.org/10.1111/acel.70707

Image Credits: AI Generated

DOI: 10.1111/acel.70707

Keywords: natural killer cells, midlife obesity, immune aging, white adipose tissue, interferon-gamma, lipid accumulation, inflammaging, high-fat diet, basal metabolic rate, NK cell maturation, cytotoxicity, Aging Cell