Browse Articles

An MR1-specific nanobody capable of blocking MR1T cell activation

Abstract MR1 is a non-polymorphic, ubiquitously expressed, MHC class I-like antigen-presenting molecule that presents small-molecule metabolites to T cells. Studies have shown that MR1 plays a role in microbial infection, inflammation, and tumor immunity. The antigens it presents include metabolites of microbial and self-origin as well as small-molecule drugs and form stable complexes with MR1 that are displayed on the cell surface to activate T cells. However, unlike classical MHC I and II molecules, the fundamental biology of MR1 remains poorly understood, particularly the mechanisms governing antigen loading and intracellular trafficking. This knowledge gap is largely due to the lack of molecular tools available to precisely manipulate MR1 function. In this study, we describe a high-affinity (1.6 nM KD) anti-MR1 nanobody, MR1Nb1. We characterize the binding of this nanobody including affinity by ELISA and kinetics by BLI. Crucially, we map the binding epitope of MR1Nb1 on MR1 by HDX-MS, providing key insights into the mechanism through which it blocks MR1T cell activation. In functional assays MR1Nb1 effectively and specifically blocks MR1T cell activation by cells infected with M. tuberculosis or treated with M. smegmatis supernatant or the synthetic ligand deazalumazine. MR1Nb1 further stains MR1-ligand complexes on the cell surface in a flow cytometry assay. This nanobody represents a unique and versatile tool for the field, as it can be produced inexpensively and expressed intracellularly within antigen presenting cells. Hence, our study provides a powerful new molecular probe for dissecting the mechanistic underpinnings of MR1 biology and uncover its broader roles in immunity.

Disease progression is associated with differential neutrophil maturation in <i>Mycobacterium tuberculosis</i> –infected macaques

Abstract Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is associated with clinical diversity and outcomes ranging from latent TB to active TB with distinct pathophysiologies. However, our understanding of the innate immune mechanisms related to the protection or progression of TB is limited. Among innate immune cells, the role of neutrophils is not fully elucidated, as they have been shown to exhibit both protective and harmful capacities in TB. We hypothesized that Mtb infection induces changes in neutrophil phenotype and function, influencing the infection outcomes. Based on clinical, bacteriological, and positron emission tomography with x-ray computed tomography (PET/CT) scan parameters, cynomolgus macaques infected by Mtb were stratified into two categories: animals that rapidly progressed to an active form of TB, designated as “fast progressors,” and “slow progressors,” which include low symptomatic or asymptomatic animals. In this study, we identified transcriptomic signatures of type I interferons and neutrophil degranulation in macaques with fast progression to active TB, which were not observed in animals with slow TB progression. Unsupervised mass cytometry analysis showed the emergence of blood immature neutrophils (CD101+ CD10−) in fast-progressing animals. In addition, bulk blood neutrophils from infected animals displayed capacities to modulate TNF-α production and cytotoxic function of CD8 T cells in a contact-dependent mechanism. In lung granulomas, neutrophils showed a tissue-specific phenotype (CD101− CD10+), with greater infiltration in animals with active TB. These data suggest that neutrophil subpopulations are associated with disease progression, with capacities to modulate CD8 T cells’ functions, which in turn may contribute to disease progression.

Metabolic adaptations of inflammatory macrophages govern ferroptosis susceptibility via the GCH1–BH4–iNOS axis

Abstract In inflammatory tissue niches, macrophages encounter intense oxidative stress due to their own production of reactive oxygen and nitrogen species as part of antimicrobial defense. Our findings reveal that inflammatory macrophages deploy distinct, context-dependent redox-protective mechanisms to survive this self-inflicted stress, thereby avoiding ferroptotic cell death. Specifically, LPS-activated macrophages, M(LPS), rely on the GTP cyclohydrolase 1 (GCH1)–tetrahydrobiopterin (BH4) pathway for ferroptosis resistance, whereas LPS + IFN-γ–activated macrophages, M(LPS–IFN-γ), depend primarily on nitric oxide produced by inducible nitric oxide synthase (iNOS)—with the BH4 pathway suppressing cell death in the absence of nitric oxide. These distinct adaptations highlight a novel GCH1–BH4–iNOS axis that governs macrophage ferroptosis susceptibility. In both the LPS or the LPS + IFN-γ–activated settings, the redox-protective phenotype is reversible: Removal of inflammatory stimuli abolishes the protection, indicating that this metabolic programming requires continuous stimulation and is not a permanently fixed state. These findings uncover redox metabolism-guided metabolic distinctions between inflammatory macrophages and reveal how they preserve viability over prolonged inflammatory activation. Ultimately, our findings establish the GCH1–BH4–iNOS axis as a central, targetable mechanism to manipulate macrophage ferroptosis resistance for therapeutic purposes.

Sleep interruption aggravates sepsis by rewiring the macrophage immune response

Abstract Sepsis is the leading cause of death in hospitals and is very common in intensive care units (ICUs). Sleep is frequently interrupted in the hospital setting, especially within the ICU. Patients who sleep poorly have worse outcomes, such as increased mortality and longer hospital stays; however, the molecular basis remains poorly understood. In this study, we utilized a mouse model to investigate the impact of sleep interruption on subsequent sepsis. We found that sleep interruption aggravated sepsis, as evidenced by higher mortality rates (88% in mice with interrupted sleep vs 57% in mice with normal sleep; P = 0.0045) and worse disease scores. This effect occurred in both females and males. Sleep interruption increased circulating T cells and CD8+ T-cell activation during sepsis. Sleep interruption also increased the levels of serum cytokines (including IL-23 before sepsis was induced, and IL-6, TNF-α, MCP-1, and IL-10 after sepsis), and amplified macrophage cytokine production ex vivo. These ex vivo effects were largely dependent on Toll-like receptor 2 (TLR2), and sleep interruption no longer exacerbated sepsis in TLR2 knockout mice. Interestingly, the effects of sleep interruption on sepsis were reversed by 48 hours of recovery sleep, consistent with a mechanism involving altered gene expression rather than epigenetic changes. RNA sequencing identified 680 genes that were significantly up- or downregulated in macrophages from animals subject to sleep interruption, including multiple genes related to pathogen defense and cytokine signaling. Our study confirms that good sleep is essential to maximize sepsis survival and provides insight into the molecular basis whereby poor sleep alters immune function.

Human XIRP1 is a new podosome protein targeting cytosolic bacteria as part of the IFN-γ defense program

Abstract Interferon-gamma (IFN-γ) is a powerful transactivating signal eliciting hundreds of IFN-stimulated genes (ISGs) in humans to help combat infection. Most ISGs remain uncharacterized, and here we searched for actin-binding candidates that could potentially target intracellular pathogens to block their spread or promote immune cell migration into infected tissues. Dual RNA-Seq and in silico mining across 1,933 data sets discovered &amp;gt;225 actin-related genes; the most highly expressed was XIRP1 (xin actin binding repeat containing 1 protein), a new ISG with no reported immune function. We found XIRP1 induction required IFN-γ plus IL-1β or exposure to pathogenic Listeria, Shigella, or Salmonella in immune and non-immune cells. Within IFN-γ-activated human macrophages, the XIRP1 protein localized to actin-rich podosomes where it formed a dome-shaped cap facing the cytosol; genetic XIRP1 ablation led to significant actin loss from these structures. Within infected cells, XIRP1 was recruited onto cytosolic Listeria monocytogenes in an ActA-dependent manner. Live imaging found many listeriae were fully encapsulated by XIRP1 whereas incomplete XIRP1 coating allowed pathogen escape from the initial coat structure. Together, our results identify XIRP1 as a new podosome-associated ISG that targets cytosolic bacteria as part of the IFN-γ-induced defense program in humans.

Distinguishing Th17 cells as a unique subset

FTR85 negatively regulates type I IFN antiviral signaling pathway by promoting K48-linked polyubiquitination of IRF3

Abstract The finTRIM (FTR) subfamily, a group of fish-specific tripartite motif proteins, has arisen through gene duplication events specific to particular genera or species. However, the regulatory mechanisms of FTR in antiviral immune response remains largely unknown. In the present study, we identified a fish novel tripartite motif member (finTRIM, FTR) in common carp (Cyprinus carpio L.) and named it CcFTR85, which contains a RING (really interesting new gene) domain, a coiled-coil region, and a PRY/SPRY domain. Its expression can be induced following spring viremia of carp virus (SVCV) infection and poly(I:C) stimulation. Overexpression of CcFTR85 significantly inhibits the expression of IFNφ1 and IFN-stimulated genes, thereby facilitating SVCV replication. Mechanistically, CcFTR85 binds to interferon regulatory factor 3 (IRF3) and promotes its K48-linked polyubiquitination at K329, causing a proteasomal degradation of IRF3 and consequent suppression of IRF3-mediated antiviral immune responses. In addition, ftr85-deficient zebrafish are more resistant to SVCV infection. Our study reveals a role for FTR85 in the regulation of antiviral responses, suggesting that it may serve as a potential target for controlling fish viral infections.

p120-catenin enhances macrophage efferocytosis and facilitates resolution of lung inflammatory injury

Abstract Defective resolution of inflammation following sepsis contributes to persistent immune dysfunction and increased morbidity and mortality worldwide. Efficient clearance of apoptotic polymorphonuclear neutrophils (PMNs) by macrophages, a process known as efferocytosis, is essential for resolving inflammation, promoting tissue repair, and restoring immune homeostasis; however, the molecular mechanisms governing this process remain poorly understood. Here, we identify p120-catenin (p120) as a critical regulator of efferocytosis that promotes the resolution of inflammatory lung injury. In alveolar macrophage–depleted mice challenged with endotoxin, intratracheal instillation of p120-deficient macrophages delayed the resolution of PMN infiltration, protein exudation, and lung edema and injury compared with control macrophages. These changes were accompanied by increased levels of TNF-α and IL-6, decreased levels of TGF-β and IL-10, and a reduced number of macrophages containing apoptotic PMNs in bronchoalveolar lavage fluid. p120 depletion also markedly reduced the phagocytosis of apoptotic PMNs by cultured macrophages. Mechanistically, p120 deficiency decreased the expression of the efferocytic receptors CD36 and Axl and shifted macrophage polarization toward a pro-inflammatory M1 phenotype. Furthermore, apoptotic cells induced the association and co-localization of p120 with peroxisome proliferator-activated receptor-γ (PPARγ), whereas p120 deletion markedly reduced PPARγ activity in response to apoptotic PMNs. Pharmacologic inhibition of PPARγ abolished p120-mediated macrophage efferocytosis and the resolution of lung inflammation. Collectively, these findings establish a central role for p120 in macrophage efferocytosis and inflammatory resolution and suggest that targeting macrophage p120 may represent a novel therapeutic strategy to promote recovery from inflammatory lung injury.

Variable fab domain N-glycosylation patterns in the B cell receptor repertoires of healthy individuals and patients with rheumatoid arthritis

Abstract N-linked glycosylation (N-glyc) sites (N-X-S/T, X≠P) can be introduced by somatic hypermutation in immunoglobulin Fab regions. In patients with rheumatoid arthritis (RA), anti-citrullinated protein antibodies have a striking overrepresentation of Fab N-glycosylation. To further explore this, we sequenced B cell receptors (BCRs) from peripheral blood of 13 RA patients and 6 healthy control subjects, analyzing in total &amp;gt;250,000 heavy chain (VH) and &amp;gt;100,000 light chain sequences from both total B cells and citrullinated fibrinogen–reactive (Cit-Fib+) cells. Distribution of variable VH genes in VDJ DNA, and transcripts of unmutated IgM and class-switched BCR, revealed transcript gene-usage bias and higher VH4 in natural rearrangements by out-of-frame VDJ DNA in RA patients compared with control subjects. IgG Fab N-glyc sites were slightly more prominent in RA than control subjects (14.9% versus 12.1%; P = 0.048) with certain VH genes (e.g. VH1-18, VH1-69, VH3-9) displaying enriched N-glyc cumulative frequencies by somatic hypermutation. VH gene N-glyc hotspots were identified, explained by a lower threshold for codon conversion (i.e. K/S/T-X-S/T) and especially frequent in VH4s. Yet, RA patients had significantly more N-glyc in complementarity-determining region (CDR) 1 and 3 compared with control subjects. Expanded clonotypes with somatic hypermutation–induced N-glyc sites were delineated by network analysis in both the RA patients and control group, but patients with RA displayed more highly mutated class-switched members. Furthermore, Cit-Fib+ BCR-expanded clonotypes could be traced in the total B cell repertoire and exhibited increased frequency of N-glyc in mutated IgG/IgA subsets. Our findings highlight how Fab N-glyc sites can be linked to biased clonotype evolution and B cell selection in chronic responses.

ENPP1-dependent USP2 ubiquitination governs SQSTM1-mediated autophagy-dependent ferroptosis in trophoblast cells and exacerbates placental dysfunction in gestational diabetes mellitus

Abstract Downregulation of ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) has been implicated in autophagic cell death. However, how ENPP1 regulates the interplay between autophagy and ferroptosis to maintain trophoblast homeostasis in the context of gestational diabetes mellitus (GDM) remains unclear. To determine ENPP1’s role in autophagy-dependent ferroptosis and its contribution to GDM-related placental injury, clinical placental tissues, hyperglycemia-treated HTR8/SVneo trophoblasts, and streptozotocin-induced GDM mice were analyzed. Ubiquitination assays, co-immunoprecipitation, functional studies, and therapeutic interventions were conducted. ENPP1 was significantly reduced in GDM placentas and correlated with increased ferroptosis and lipid peroxidation. Mechanistically, ENPP1 recruited USP2 (ubiquitin-specific peptidase 2) to inhibit the ubiquitination and autophagic degradation of SQSTM1 (sequestosome 1), thereby enhancing its stability. ENPP1 loss promoted NCOA4-mediated ferritinophagy, leading to iron overload and ferroptosis. Restoring ENPP1 or inhibiting autophagy alleviated placental thinning and fetal growth restriction in GDM mice. ENPP1 regulates autophagy-dependent ferroptosis via the USP2–SQSTM1 axis, and its deficiency contributes to placental dysfunction.

The V158F polymorphism in human FcγRIIIa/CD16a defines opposing receptor responses when interacting with soluble immune complexes

Abstract The V158F polymorphism found in the human Fc receptor CD16a (also known as FcγRIIIa) is thought to influence autoimmune disorders and responses to IgG-based therapies. V158F is known to influence the IgG affinity, and thereby triggering of the CD16a receptor expressed on various immune cells. In contrast to CD16 triggering by opsonized IgG, the mechanistic details of its interaction with soluble circulating IgG immune complexes (ICs) remain poorly understood. In this study we aimed to clarify the functional impact of the CD16a-V158F polymorphism in the context of IC-mediated diseases. We generated BW5147 reporter cells for both human CD16a V158F polymorphic variants. Using synthetic and disease-associated soluble IgG ICs, we assessed their respective functional responses, which were further validated using primary human NK cells. While both reporter cell variants bound ICs, the CD16aV but not the CD16aF reporter cells exhibited functional response to soluble ICs. This functional dichotomy was further confirmed in primary CD16+ human NK cells. We provide evidence for an intrinsic difference between V158F polymorphic variants of human CD16a in their responsiveness to soluble ICs, extending beyond the previously reported distinctions of low- and high-affinity binding. Future studies investigating genotype-dependent clinical-immunological differences could enhance our understanding of the pathophysiology in IC-mediated diseases and pave the way for potential individualized treatment strategies.

Incorporation of multiple diversity genes in the TCRδ chain is highly regulated and evolutionarily conserved

Abstract In the canonical model of VDJ recombination, a single diversity (D) gene is incorporated into the complementarity-determining region 3 (CDR3) to produce a T cell receptor δ (TCRδ; TRD) or TCRβ (TRB) chain. But by constructing a dataset of more than 2.7 million TRD CDR3 sequences from 6 species (human, mouse, cattle, sheep, naked mole-rat, and rabbit), we found that incorporation of more than one D gene in the same CDR3 is strikingly high and evolutionarily conserved in the TRD CDR3, while remaining minimal in the TRB CDR3. These high frequencies are favored by TRD locus architecture and configuration of 12/23-bp recombination signal sequences (RSSs). Multiple D gene incorporation is further shaped by V (variable) gene usage and age, and is especially enriched in adaptive-like γδ T cells. This regulation is established in the thymus at the level of hematopoietic stem and precursor cells, driven by the RNA-binding protein LIN28B. Thus, genomic design, recombination constraints, and developmental timing regulate the frequencies of multiple D gene incorporation, closely associated with γδ T cell biology.

CCR6-CCL20 signaling modulates immunoglobulin isotype switching at the mucosal barrier during gut inflammation

Abstract Chemokine CCL20, secreted by gut epithelial cells, demonstrates markedly increased expression during episodes of chronic inflammation and infection. Mucosal barriers recruit more CCR6+ B cells and have higher immunogloblin A (IgA) Ab levels during normal, infectious, and inflammatory states. Ig isotypes at the mucosal surface are pivotal in modulating inflammatory responses and controlling infections. However, the intrinsic signaling pathway mediated by CCR6-CCL20 in B cells—in particular, its impact on Ig isotype expression—remains insufficiently investigated. In this study, the dextran sodium sulfate (DSS)–induced gut inflammation model in C57BL/6 mice was used. Our findings indicate that DSS administration elevates CCL20 production in the gut epithelium, which, in turn, enhances the differentiation of IgA+ B cells in gut-associated lymphoid tissues, while concurrently reducing both IgG1+ B-cell populations and serum IgG1 levels, in a CCR6-dependent manner. Furthermore, stimulation with CCL20 through CCR6 induces phosphorylation of the AKT/mTOR/STAT3 signaling pathways in B cells. Pharmacological inhibition of mTOR signaling with rapamycin effectively abrogated CCL20-driven differentiation of IgA+ B cells. Collectively, these results suggest a significant role for CCR6-CCL20 signaling, alongside other costimulatory mechanisms, in regulating Ig isotype switching at the mucosal barrier during intestinal inflammation, thereby offering important insights into CCR6-mediated inflammatory pathologies.

Comment on “Toward clinically actionable explainable AI in pulmonary arterial hypertension: Endpoints, calibration, and external validation”

A novel monocyte-derived antigen presenting cell-T regulatory cell axis contributes to skin wound healing and is impaired in diabetic mice

Abstract Despite a vast literature on the role of macrophages in wound healing, the role of dermal monocyte (Mo)-derived antigen presenting cells (APC) has received scant attention. Using scRNAseq and flow cytometry, we identify a population of APC that is prominent in wounds of non-diabetic mice but is reduced in wounds of diabetic mice. Using adoptive transfer experiments and Ccr2 knockout mice, we demonstrate that wound APC are derived primarily from Mo and that the diabetic wound environment inhibits differentiation of Mo into APC. We also show that Mo-specific Irf4 knockout mice exhibit reduced differentiation of Mo into APC, decreased levels of IL-27 and numbers of activated Treg cells in wounds. and impaired wound healing. Importantly, adoptive transfer of bone marrow Mo that express Irf4 into wounds of Mo-specific Irf4 knockout mice rescued levels of wound APC and activated Treg, as well as wound healing. Local administration of recombinant IL-27 into wounds of these mice also rescued levels of activated Treg in wounds, along with wound healing, Together, these findings identify a novel pathway in which IRF4 induces Mo differentiation into APC in wounds, which in turn produce IL27 that activates Treg to promote healing. This pathway is impaired in wounds of diabetic mice, which provides a novel target to improve diabetic wound healing.

Fate mapping reveals a prenatal-to-neonatal wave of ILC2s with a history of <i>Cd3g</i> expression

Abstract Group 2 innate lymphoid cells (ILC2s) are thought to develop in the bone marrow and fetal liver. However, increasing evidence supports the presence of thymic ILC2s in mice and humans. In this study, we introduce a novel fate-mapping mouse model designed to track thymic ILC2s in peripheral tissues. Thymic ILC2s are labeled by ZsGreen, whose expression is induced by Cd3giCre. While they are present in the thymus and peripheral tissues, they are not found in the bone marrow. These cells are predominantly abundant during the neonatal stage, when the intense lung alveolarization and tissue remodeling occur. RNA sequencing revealed elevated expression of cytokine genes Il13 and Il4, as well as Klrg1, in these cells. They also harbor TCR gene rearrangements, suggesting common developmental pathways with T cells. Furthermore, we demonstrate that neonatal ILC2s play a critical role in macrophage polarization in a naphthalene-induced lung injury model. These findings help explore the differences between pediatric and adult immunity and future therapeutic strategies.

Antigen-presenting cancer-associated fibroblasts in murine pancreatic tumors differentially regulate T-cell phenotype and function

Abstract Pancreatic ductal adenocarcinoma (PDAC) is characterized by an immunosuppressive tumor microenvironment (TME) in which cancer-associated fibroblasts (CAFs) play pivotal roles in shaping therapeutic responses. Among these, MHC-II–expressing antigen-presenting CAFs (apCAFs) modulate CD4 T-cell activity, yet their contribution to the antitumor immune response remains unclear. Using tumor clones of the KPC murine PDAC model differing in sensitivity to immune checkpoint blockade (ICB), we show that immunosensitive (sKPC) tumors exhibit greater apCAF infiltration than resistant (rKPC) tumors. Reducing apCAF numbers in sKPC tumors impaired responsiveness to ICB, highlighting apCAFs’ role in mediating effective antitumor immunity. Ex vivo assays revealed that apCAFs from both models activate CD4 T cells and induce regulatory T-cell (Treg) differentiation. However, single-cell transcriptomics revealed that rKPC apCAFs promote Tregs with heightened immunosuppressive signatures, driven by distinct chemokine signaling. We identified elevated CCL22 expression and signaling in rKPC-derived apCAFs as a contributor to enhanced Treg-mediated suppression. Functional blockade of CCL22 reduced TGF-β secretion by rKPC apCAF-induced Tregs, supporting a mechanistic role for this pathway in fostering an immunosuppressive TME. These findings position apCAFs as regulators of CD4 T-cell antitumor immunity in PDAC and suggest that modulating apCAF–T-cell interactions could offer strategies to enhance immunotherapy efficacy.

Sustained antigen-specific CD8+ T cell immunity post–mRNA booster requires notch pathway activation

Abstract Messenger RNA (mRNA) vaccines effectively induce protective immunity, but antigen-specific CD8+ T cell responses exhibit limited persistence. In this study, we aimed to assess CD8+ T cell responses following a third dose of the Pfizer BNT162b2 COVID-19 vaccine and identify factors contributing to their longevity. Using HLA tetramers, we analyzed antigen-specific CD8+ T cells in 141 vaccinated individuals (86.5% female) and identified 2 groups: those with strong responses (strong group) and those with weak responses (weak group) 6 mo after the third mRNA vaccination. Transcriptomic analysis revealed that Notch signaling was upregulated in the strong group, and in vitro, the inhibition of Notch signaling significantly reduced CD8+ T cell expansion. These findings suggest that Notch signaling may contribute to maintain long-term antigen-specific CD8+ T cell responses following mRNA vaccination. Targeting this pathway could offer novel strategies for enhancing vaccine-induced cellular immunity and long-lasting protection.

Differential stem-like potential of naïve and memory CD8 T cells after chronic infection

Abstract Memory CD8 T cells respond rapidly upon antigen re-encounter and are considered advantageous for protective immunity. However, they undergo a swift decline under chronic antigen stimulation. In this study, we found that memory CD8 T cells’ heightened activation sensitivity promotes terminal differentiation and impairs the formation of CXCR5+Tim-3− progenitor subsets, resulting in reduced persistence. This defect was commonly observed in memory CD8 T cells generated by diverse immunization strategies. Mechanistically, their inability to generate progenitor cells was not due to insufficient expression of TCF1 or TOX upregulation. Importantly, blockade of type I interferon signaling during priming restored progenitor differentiation of secondary activated CD8 T cells. These findings highlight that the activation context of memory CD8 T cells critically influences their fate during persistent infection and suggest that modulating inflammatory signals may enhance the durability of secondary responses.

Distinct immune trajectories after severe trauma identify a Th17-biased immunophenotype in chronic critical illness

Abstract Severe trauma triggers a dynamic disturbance of immune function that can progress from early hyperinflammation to prolonged dysregulation, increasing patient vulnerability to infection and chronic critical illness (CCI). To identify immune features linked to different postinjury clinical trajectories, we prospectively evaluated severely injured trauma patients and categorized them as rapid recovery, intermediate, or CCI based on clinical outcome by day 14 of intensive care unit admission. CCI patients developed infections earlier and more frequently than rapid recovery or intermediate patients, with nearly one-third experiencing their first infection (primarily pneumonia) within 4 d of intensive care unit admission and &amp;gt;80% did so within 8 d. Immune profiling showed trauma-associated alterations across all groups, including neutrophilia and early T cell lymphopenia. However, CCI patients exhibited a distinct immunophenotype characterized by elevated neutrophil counts, recovery of total CD3+ T cells by day 7, preserved inducible interferon γ (IFNγ) production, and a selective expansion of CD4+ T helper 17 (Th17) cells. Functional assays revealed sustained or amplified T cell cytokine responses in CCI patients, including persistent IFNγ and interleukin (IL)-17A production. Plasma cytokine analysis further demonstrated prolonged elevation of IL-17A, IL-17C, IFNγ, and IL-10, indicating a mixed but enduring pro- and anti-inflammatory state. These findings suggest that CCI after trauma is not driven by classic immunosuppression, but rather is driven by an IL-17–skewed immune program coupled with ineffective pathogen control. The persistent Th17/neutrophil axis may contribute to heightened infection risk and progression to CCI, highlighting dysregulated IL-17–mediated innate and adaptive circuits as a potential mechanism of ongoing immune dysfunction following severe trauma.