The research team, led by Zhe Gao and Xin Zhang, set out to explore a question that has remained surprisingly open: what role, if any, does TRIM28 play in regulating the behavior of macrophages and the keratinocytes they communicate with? TRIM28, short for tripartite motif-containing 28, is a multifunctional protein best known for its involvement in transcriptional regulation and epigenetic modification. It can influence protein stability through ubiquitination and SUMOylation, two post-translational modifications that attach small protein tags to targets and alter their behavior. Despite growing interest in TRIM family proteins across immunology and cancer biology, TRIM28’s role in macrophage polarization had not been clearly defined.

To probe this question, the researchers used a well-established laboratory model. They cultured human THP-1 monocytic cells and differentiated them into macrophage-like cells using a chemical called phorbol 12-myristate 13-acetate. Separately, they maintained HaCaT keratinocytes, an immortalized human skin cell line. Using small interfering RNAs, they silenced TRIM28 expression in the macrophages, and in complementary experiments they boosted TRIM28 levels using an overexpression plasmid. These two approaches, gene knockdown and gene overexpression, allowed the team to observe what happens when TRIM28 is removed or amplified within the same cellular environment.

The results were striking. When TRIM28 was silenced, flow cytometry analysis revealed a marked shift in macrophage phenotype: the proportion of CD68-positive CD206-positive cells, associated with an M2-like or anti-inflammatory profile, increased to 25 percent from lower baseline levels. Conversely, the proportion of CD68-positive CD86-positive cells, associated with an M1-like or pro-inflammatory profile, dropped to just 5 percent. Enzyme-linked immunosorbent assays confirmed the functional consequences: silencing TRIM28 reduced secretion of the pro-inflammatory cytokines IL-6 and TNF-α while increasing the anti-inflammatory cytokine IL-10. Western blotting reinforced these findings, showing decreased expression of the M1-associated marker iNOS and increased expression of the M2-associated marker Arg1. When TRIM28 was overexpressed, every one of these trends reversed, pushing macrophages toward the pro-inflammatory state.

The team then traced the molecular pathway underlying this effect. Prior research had suggested that TRIM28 can stabilize NLRP3, a key component of the inflammasome, a multiprotein complex that triggers inflammatory signaling. NLRP3, in turn, is known to activate its downstream partner SGT1. In the current study, TRIM28 knockdown reduced the expression of both NLRP3 and SGT1, while overexpression raised their levels. Crucially, the researchers also examined functional readouts of inflammasome activation. TRIM28 knockdown decreased levels of cleaved caspase-1 and mature IL-1β, both hallmarks of inflammasome activity, and reduced secretion of IL-1β into the culture medium. Overexpression produced the opposite pattern. Co-immunoprecipitation experiments further revealed that TRIM28 physically interacts with NLRP3 and that TRIM28 overexpression significantly increased the SUMOylation of NLRP3, a modification previously linked to inflammasome stabilization.

With the macrophage-side mechanism established, the investigators turned to the keratinocyte side of the equation. They placed modified macrophages in the upper chamber of a Transwell system, separated by a porous membrane from HaCaT keratinocytes below, allowing soluble factors to pass but preventing direct cell contact. After 24 hours of co-culture, they measured keratinocyte viability and invasive capacity. The differences were dramatic. Co-culture with TRIM28-silenced macrophages reduced HaCaT cell viability to 60 percent of control levels, while co-culture with TRIM28-overexpressing macrophages raised viability to 140 percent. Invasion assays showed a similar pattern: silencing TRIM28 in macrophages reduced keratinocyte invasion to 60 percent of baseline, whereas overexpression increased it to 180 percent. These cellular behaviors, hyperproliferation and invasion, are relevant to inflammatory skin responses, although the authors are careful to note that they do not by themselves demonstrate a role for TRIM28 in psoriasis in living organisms.

To confirm that the NLRP3/SGT1 axis and SUMOylation were genuinely required for these effects rather than incidental, the researchers performed a series of rescue experiments. They knocked down NLRP3 or SGT1 in macrophages overexpressing TRIM28, or treated the cells with 2-D08, a chemical inhibitor of SUMOylation. Each intervention partially reversed the TRIM28-driven shift toward the pro-inflammatory macrophage phenotype, restoring the balance of CD86-positive and CD206-positive populations. The interventions also normalized cytokine secretion patterns, reduced cleaved caspase-1 and mature IL-1β levels, and attenuated the enhanced NLRP3 SUMOylation. Most importantly, these same interventions partially reversed the proliferative and invasive changes observed in co-cultured keratinocytes, confirming that the NLRP3/SGT1 pathway and SUMOylation are functionally required for the macrophage-mediated effects on skin cells.

The study places TRIM28 within a growing family of TRIM proteins implicated in inflammatory skin biology. Previous work has shown that TRIM14 promotes psoriasis-like inflammation by activating NF-κB signaling, and that TRIM27 amplifies IL-6/STAT3 signaling in keratinocytes. The current research extends this picture by suggesting that TRIM28 operates through a distinct mechanism, one involving post-translational modification of the NLRP3 inflammasome rather than transcriptional regulation alone. This positions TRIM28 as a potential bridging molecule between the epigenetic machinery of the cell and the innate immune response, a role that has parallels in other inflammatory conditions. The researchers draw comparisons to the HSP90β-SGT1 complex, which stabilizes NLRP3 in autoinflammatory syndromes, and to studies in fatty liver disease where HSP90 inhibition suppresses NLRP3 activation.

Nevertheless, the authors are emphatic about the limitations of their work. All experiments were performed in simplified in vitro systems using immortalized cell lines, which cannot fully replicate the cellular diversity, tissue architecture, and immune microenvironment of human psoriatic skin. The team did not examine TRIM28 expression in actual psoriatic lesions, did not analyze patient-derived samples, and did not correlate TRIM28 levels with disease severity. Macrophage polarization was assessed using a limited marker panel, and the authors acknowledge that the M1/M2 framework is a simplified operational model rather than a definitive classification of macrophage states. More comprehensive approaches, including single-cell RNA sequencing and multiplex flow cytometry, would be needed to fully characterize the macrophage phenotypes regulated by TRIM28. Additionally, the specific enzyme responsible for NLRP3 SUMOylation in this context remains unknown, as TRIM28 itself lacks SUMO ligase activity, suggesting intermediary proteins may be involved.

Looking forward, the researchers outline several priorities for future investigation. They propose examining TRIM28 expression and localization in human psoriatic tissue alongside clinical markers, validating the TRIM28–NLRP3/SGT1 axis in patient-derived cells and three-dimensional organotypic skin cultures, and testing whether modulating TRIM28 alters inflammation in animal models of psoriasis-like dermatitis. They also call for a more precise mapping of the molecular interactions between TRIM28, NLRP3, and SGT1, including identification of the relevant SUMO E3 ligase and assessment of downstream inflammasome assembly events. Until such work is completed, the current study stands as a rigorous piece of mechanistic cell biology, defining a TRIM28-dependent inflammatory pathway in a controlled laboratory setting. Its contribution is foundational rather than translational: it illuminates how a single regulatory protein can reshape the inflammatory conversation between two cell types central to skin immunity, while leaving open the critical question of whether that conversation drives human disease.

Subject of Research: TRIM28 regulation of macrophage polarization and keratinocyte behavior via the NLRP3/SGT1 axis in vitro

Article Title: TRIM28 Promotes Keratinocyte Proliferation and Invasion by Activating NLRP3/SGT1 Axis‐Mediated Macrophage Pro‐Inflammatory Polarization in an In Vitro Macrophage–Keratinocyte Co‐Culture Model

Article References: Gao, Z., Zhang, X., Wang, J., & Yang, N. (2026). TRIM28 Promotes Keratinocyte Proliferation and Invasion by Activating NLRP3/SGT1 Axis‐Mediated Macrophage Pro‐Inflammatory Polarization in an In Vitro Macrophage–Keratinocyte Co‐Culture Model. Immunity, Inflammation and Disease, 14(9), Article e70522. https://doi.org/10.1002/iid3.70522

Image Credits: AI Generated

DOI: 10.1002/iid3.70522

Keywords: TRIM28, macrophage polarization, NLRP3 inflammasome, SGT1, SUMOylation, keratinocytes, psoriasis, inflammation, IL-1β, co-culture, innate immunity, skin biology

Non-tuberculous mycobacteria, often abbreviated NTM, are environmental organisms that increasingly cause chronic and debilitating lung disease worldwide. Among them, Mycobacterium abscessus stands out as particularly menacing. It is naturally resistant to many standard antibiotics, it can form ropelike cords that shield it from engulfment by immune cells, and it thrives in patients with pre-existing lung damage such as bronchiectasis, cystic fibrosis, or pulmonary fibrosis. Treatment regimens typically stretch for many months, involve multiple toxic drugs, and frequently fail to eradicate the infection. Against this grim clinical backdrop, the question of how the immune system naturally fights M. abscessus has remained surprisingly underexplored, particularly with respect to γδ T cells, an unconventional lymphocyte population whose role in NTM infection had never been systematically characterized.

γδ T cells differ from the conventional αβ T cells that dominate textbook immunology. Rather than recognizing peptide fragments presented by major histocompatibility molecules, they respond rapidly to a wide range of stress signals and microbial products, earning them a reputation as a bridge between innate and adaptive immunity. A major subset of these cells produces interleukin-17A, a powerful inflammatory cytokine best known for recruiting neutrophils and shaping defenses at body surfaces. To determine whether these cells matter in M. abscessus infection, the researchers built a mouse model of pulmonary infection and mapped the immune landscape of lung tissue over the early days of disease using single-cell RNA sequencing, a technique that captures the gene expression profile of thousands of individual cells simultaneously.

The single-cell atlas revealed a striking pattern. As infection took hold, γδ T cells accumulated in the lung and expanded a population that expressed high levels of IL-17A. When the team removed γδ T cells entirely, using mice genetically engineered to lack them, the consequences were dramatic: bacteria persisted at far higher levels in the lungs and spleens, and lung inflammation worsened. Conversely, when γδ T cells were depleted in animals that had already cleared a first infection and were then re-challenged, the protective advantage of prior exposure evaporated. These experiments established γδ T cells as indispensable players in the early defense against M. abscessus, a finding that had not been demonstrated before for any non-tuberculous mycobacterial pathogen.

Delving deeper, the investigators identified IL-17A itself as the linchpin of this protective response. Mice unable to produce IL-17A lost much of their capacity to control the infection, and importantly, the defect traced back to the γδ T cells themselves. Without IL-17A signaling, the cells became less adept at recognizing the bacterium and lost much of their cytotoxic firepower. In an elegant series of transfer experiments, IL-17A-deficient γδ T cells failed to protect infected animals, whereas their normal counterparts succeeded. This revealed something unusual: IL-17A was not merely acting as a broadcast signal to other immune players but was required within the γδ T cells themselves, a cell-intrinsic requirement that underscores how tightly the cytokine and its producer are wired together during this infection.

The mechanism by which these cells actually kill the bacterium proved to be equally instructive. M. abscessus is an extracellular pathogen during key phases of infection, residing outside host cells in the airways and tissue spaces. The researchers found that IL-17A-positive γδ T cells eliminated extracellular bacteria through a granzyme B-dependent cytotoxic pathway. Granzyme B is a serine protease classically associated with the destruction of virus-infected or malignant cells, delivered through pore-forming perforin or other release mechanisms. Its deployment against free-living bacteria adds a new dimension to the antimicrobial portfolio of γδ T cells and explains how a lymphocyte population usually discussed in the context of autoimmunity and inflammation can act as a direct bactericidal weapon.

How, then, does the immune system know to mobilize these cells in the first place? The answer lies in a cascade that begins with Toll-like receptor 2, a pattern-recognition receptor on macrophages that detects components of the bacterial cell wall. When M. abscessus engaged TLR2 on lung macrophages, the macrophages responded by secreting two cytokines, interleukin-1β and interleukin-23. This cytokine pair is a well-known stimulus for IL-17 production in T cells, and in this context it drove both the expansion and the activation of the IL-17A-positive γδ T cell population. Blocking either IL-1β or IL-23 in infected mice diminished the γδ T cell response and impaired bacterial control, mapping out a complete signaling axis that runs from bacterial recognition through macrophage activation to lymphocyte mobilization and, ultimately, bacterial killing.

Perhaps the most clinically resonant aspect of the study concerns patients whose immunity depends on interferon-gamma, the canonical cytokine for defense against mycobacteria. A subset of individuals, particularly in Southeast Asia, develops autoantibodies that neutralize their own interferon-gamma, leaving them exquisitely vulnerable to disseminated NTM infections. Using single-cell RNA sequencing of peripheral blood cells from NTM patients, the researchers found evidence that anti-interferon-gamma autoantibodies compromise γδ T cell function in humans, mirroring what they observed in mice lacking the interferon-gamma receptor. Crucially, in mice engineered without functional interferon-gamma signaling, IL-17A-positive γδ T cells still conferred protection, and the same held true in a model combining M. abscessus infection with bleomycin-induced pulmonary fibrosis. In other words, this arm of immunity operates independently of the interferon-gamma axis and remains effective even in scarred, damaged lungs.

The implications for therapy are considerable. Current treatment of NTM disease relies almost entirely on antibiotics that the pathogen is adept at resisting, and there are no licensed immunotherapies that bolster host defenses. If the pathways defined in this study can be harnessed in patients, whether by stimulating IL-1β and IL-23 signaling, expanding protective γδ T cell populations, or delivering IL-17A-driven cytotoxic activity directly, clinicians could gain a means of strengthening the lung’s own antimicrobial machinery. Such approaches would be especially valuable for the growing population of patients with anti-interferon-gamma autoantibodies or structural lung disease, for whom conventional regimens offer diminishing returns. The researchers caution that translating mouse findings to the clinic will require careful work, particularly because IL-17A is also implicated in inflammatory conditions such as psoriasis and could carry safety risks if induced systemically. Nevertheless, the identification of a concrete, mechanistically defined cell type that can clear M. abscessus marks a genuine advance. It transforms γδ T cells from immunological bystanders into a promising therapeutic target, and it reframes the fight against antibiotic-resistant mycobacteria as a battle that the immune system, with the right encouragement, may be able to win on its own terms.

Subject of Research: The role of IL-17A-producing γδ T cells in controlling pulmonary Mycobacterium abscessus infection in mice.

Article Title: IL-17A-producing γδ T cells control pulmonary Mycobacterium abscessus infection in mice

Article References: Hu, X., Lin, S., Meng, W., Liu, H., Qin, Z., Wu, Z., Wan, Y., Ma, S., Yang, X., Yin, Z., Chu, Y., Zhang, W., Shao, L., & Lin, Y. (2026). IL-17A-producing γδ T cells control pulmonary Mycobacterium abscessus infection in mice. Nature Microbiology. https://doi.org/10.1038/s41564-026-02466-5

Image Credits: AI Generated

DOI: 10.1038/s41564-026-02466-5

Keywords: Mycobacterium abscessus, non-tuberculous mycobacteria, γδ T cells, IL-17A, interferon-gamma, granzyme B, TLR2, IL-1β, IL-23, pulmonary infection, immunology, antibiotic resistance