ImmunoHorizons

T cell activation is associated with, and dependent upon, the upregulation of amino acid uptake from the extracellular environment. Uptake of the non-essential amino acid asparagine (Asn) is mediated via amino transporters such as Slc1a5 whilst Asn can be synthesized within cells that express asparagine synthetase (ASNS). Previous work demonstrated that initial activation of CD8+ T cells is perturbed in the absence of Asn, whereas effector cytotoxic T cells cells upregulate ASNS and lose their dependence on Asn uptake. By contrast, less is known of the role of Asn uptake and ASNS in CD4+ T cell responses. Here we demonstrate that CD4+ T cells are more reliant than CD8+ T cells on Asn uptake for initial activation, differentiation, metabolic reprogramming and regulation of autophagy. These phenotypes are associated with enhanced expression of ASNS in CD8+ as compared to CD4+ effector T cells.

Immune memory responses are rapid and qualitatively distinct from primary responses. They typically develop in the presence of antigen-experienced memory T and B cells and pre-existing antibodies. Although the contribution of T and B cells to recall responses is well defined, the contribution of antibody "memory" and the mechanisms by which pre-existing antibodies modulate the development of germinal center and plasma cell responses is not precisely understood. Here we report on mechanisms that mediate antibody enhancement of germinal center (GC) and plasmablast (PB) compartments, and the parallel process by which they change the affinity threshold for B cell recruitment into immune responses. The data indicate that antibody-mediated enhancement of GC and PB responses is Fc gamma receptor (Fc{gamma}R) dependent and largely complement receptor 1 and 2 (CR1/2) independent. In contrast, the reduction in the affinity threshold for GC entry is independent of both Fc{gamma}Rs and CR1/2. SummaryCipolla et al. show that antibody can modulate immune responses via both Fc gamma receptor dependent and independent mechanisms. These mechanisms influence both the magnitude and composition of the germinal center response.

Mounting evidence indicates that T cells can operate in an innate-like mode challenging the classical description of T cells as strictly adaptive immune effectors. T cells can engage innate pattern recognition receptors to mount rapid but antigen-nonspecific responses to infection or cellular stress. This study observed that CD8+ T cells, and to a lesser extent also CD4+ T cells, responded to viral proteins in the mouse lung quickly in an innate-like fashion. We employed intravital lung microscopy to visualize infiltration of CD8+ T cells into the lung following intratracheal instillation of the SARS-CoV-2 envelope (E)-protein. Here, we demonstrate acute recruitment of CD8+ from the pulmonary microcirculation into the lung as early as 4 and 24 hours after (E)-protein instillation. The acute infiltration of CD8+ T cells was not observed in Tlr2-/- mice. Immunohistochemistry analysis of mouse lungs revealed T cell accumulation in nodular inflammatory foci (NIF) of the lung at perivascular regions and around large airways. Stimulating spleen-derived CD8+ T cells from wild-type mice with (E)-protein ex vivo in combination with cytokines or TCR agonists significantly upregulated CD69 and activated secretion of interferon (IFN){gamma} which was not observed with CD8+ T cells isolated from Tlr2-/- mice. These findings indicate rapid bystander activation of CD8+ T cells by the SARS-CoV-2 envelope (E)-protein that depends on (E)-protein sensing by TLR2. This innate-like CD8+ T cell response to SARS-CoV-2 (E)-protein may offer novel opportunities for diagnostic and therapeutic development, warranting further investigation.

Regulatory T cells (Tregs) are essential for maintaining immune homeostasis by suppressing excessive activation of effector T cells. Although several mechanisms of Treg-mediated suppression have been described, the molecular signals that contribute to this regulation remain incompletely understood. WNT signaling, best known for its roles in development and tissue homeostasis, has recently emerged as an important regulator of immune function, but its contribution to Treg-mediated immune suppression is largely unknown. Here, we show that Tregs preferentially express multiple canonical WNT ligands, including WNT2B, WNT3, WNT7B, and WNT10B, compared with conventional CD4+ T cells. These WNT proteins were detected intracellularly in Tregs, and WNT2B and WNT3 were actively secreted into culture supernatants. Conventional CD4+ T cells expressed Frizzled receptors capable of sensing these ligands. Pharmacological inhibition of canonical WNT signaling using the antagonist mDKK-1 enhanced CD4+ T cell activation and proliferation and increased pro-inflammatory cytokine expression, while anti-inflammatory IL-10 remained unchanged. Together, these findings identify Tregs as a source of canonical WNT ligands and suggest that Treg-derived WNT signaling contributes to the suppression of effector CD4+ T cell responses. This work reveals a previously underappreciated pathway through which Tregs regulate immune activity and identifies WNT signaling as a potential target for modulating inflammatory immune responses.

BackgroundT helper 2 (Th2) lymphocytes orchestrate type-2 immunity and drive allergic diseases that disproportionately affect females. Sexual dimorphism in Th2 responses is well-documented, yet current models attribute sex differences exclusively to circulating gonadal hormones and sex chromosomes. Whether cell-intrinsic steroidogenesis, mediated by the enzyme Cyp11a1, contributes to female-biased Th2 differentiation and function remains unknown. MethodsTranscriptomes of in vitro generated Th2 cells from male and female T cell-specific Cyp11a1-knockout (Cyp11a1fl/fl;Cd4Cre) and control (Cyp11a1fl/fl) mice were compared. Differential expression, hallmark pathway analysis, transcription factor activity scoring, and functional assays were performed across sexes and genotypes. Cyp11a1-dependent differentially expressed genes were integrated with sex-stratified human Th2 transcriptomes obtained from the type-2 inflammatory skin disease atopic dermatitis. ResultsCyp11a1 deletion markedly reduced the transcriptional signature distinguishing female from male Th2 cells. Female Cyp11a1-knockout Th2 cells underwent extensive transcriptomic reprogramming converging toward the male profile, while male cells were largely unaffected. Female-specific pathway changes included reduced inflammatory signatures and enhanced cell-cycle programmes. Functionally, female Cyp11a1-deficient Th2 cells exhibited significantly increased proliferation and elevated IL-13 production; male knockout cells showed no comparable changes. These effects were developmentally stage-specific, emerging during Th2 differentiation but not in naive precursors. Cross-species analysis identified a conserved gene module shared between Cyp11a1-deficient female mouse Th2 cells and female-biased human Th2 cells in atopic dermatitis. ConclusionsCyp11a1-mediated steroidogenesis is a cell-intrinsic regulator of the female-biased Th2 transcriptional and functional state, identifying de novo steroidogenesis as a mechanism of immunological sexual dimorphism with direct relevance for female-predominant allergic disease.

AbstractRegulatory T cells (Tregs) prevent autoimmunity through suppressive functions largely programmed by the transcription factor FOXP3. Healthy humans express approximately equivalent levels of two major alternatively spliced isoforms of FOXP3: a full-length version containing all coding exons (FOXP3-FL) and a version lacking exon 2 (FOXP3-{Delta}E2). However, sole FOXP3-{Delta}E2 expression causes lethal IPEX syndrome, and the FOXP3-{Delta}E2 isoform is elevated in several autoimmune diseases. These observations strongly suggest defects in suppression by FOXP3-{Delta}E2 Tregs which we investigated here using Foxp3-{Delta}E2 mice. In an influenza virus infection model, Foxp3-{Delta}E2 mice had an increased magnitude of the CD8+ T cell response during acute and memory formation phases of infection. Transcriptomic and chromatin accessibility analyses of homeostatic Foxp3-{Delta}E2 Tregs revealed impaired Treg programming, including reduced expression of inhibitory molecules such as Il2ra and chemokine receptors. Decreased cell surface CD25 expression on Foxp3-{Delta}E2 Tregs was associated with reduced IL-2 responsiveness in Foxp3-{Delta}E2 Tregs and, reciprocally, increased IL-2 responsiveness in CD8+ T cells from Foxp3-{Delta}E2 mice. Additionally, altered chemokine receptor expression resulted in diminished localization of Foxp3-{Delta}E2 Tregs to the T cell zone of the inflamed lymph node. Thus, Treg programming by the Foxp3-{Delta}E2 isoform impairs suppressive function, resulting in failure to restrain CD8+ T cells and aberrant immune responses. One Sentence SummaryFoxp3-{Delta}E2 expressing regulatory T cells have altered cellular programming which impairs their IL-2 sink function and co-localization with conventional T cells during priming, enhancing CD8+ T cell responses.

Mitochondrial dynamics are critical for T cell activation, differentiation, and survival. The inner mitochondrial membrane ATP-dependent metalloprotease YME1L1 regulates proteostasis and the processing of optic atrophy protein 1 (OPA1), thereby shaping mitochondrial cristae architecture and respiratory function in many cell types. Whether YME1L1 fulfils similar roles in lymphocytes remains unknown. Here, we examined YME1L1 function in T cells using conditional knockout mice lacking YME1L1 in lymphocytes (YME1L1{Delta}TB). YME1L1 expression increased upon T cell activation, yet its absence did not alter thymic development, peripheral T cell homeostasis, or the proportions of naive, memory, and regulatory subsets. T cell activation and proliferation in response to anti-CD3{varepsilon} stimulation were also unaffected. Mitochondrial parameters such as mass, membrane potential, and reactive oxygen species production, were largely preserved, with only modest, transient increases in oxidative stress detected in CD4 T cells lacking YME1L1. Electron microscopy revealed no major changes in mitochondrial size or roundness but showed increased cristae branching and reduced tortuosity, indicating subtle alterations in ultrastructure. Additionally, {gamma}{delta} T cells in YME1L1{Delta}TB mice exhibited a mild shift toward interferon-{gamma}-producing phenotypes at the expense of interleukin-17-producing subsets. Collectively, our data indicate that YME1L1, despite its requirement for OPA1 cleavage, is dispensable for T cell development and acute activation but may contribute to fine-tune mitochondrial architecture and {gamma}{delta} T cell effector programming. These findings highlight cell-type-specific redundancies in mitochondrial quality control and underscore the value of negative data in refining the understanding of mitochondrial regulation in immune cells.

Cholesterol immunometabolism is a critical controller of immunopathology in respiratory infections such as tuberculosis. Smith-Lemli-Opitz syndrome (SLOS) patients are affected by a loss of 7-dehydrocholesterol reductase (DHCR7) function and have elevated 7-dehydrocholesterol (7DHC) and reduced cholesterol. Increased 7DHC has been found to be protective against viral infections in a range of infection models however SLOS patients have a higher susceptibility to respiratory infection. Here we use the zebrafish-Mycobacterium marinum infection model to demonstrate a compromised innate immune response to bacterial infection in the absence of dhcr7. We correlate increased 7DHC with increased activation of the IRF3/type I interferon axis and demonstrate Irf3 is a targetable signaling node to restore anti-bacterial immunity in a dhcr7-depleted background. Plain English summaryLoss of 7-dehydrocholesterol reductase causes Smith-Lemli-Opitz syndrome. One of the metabolic features of Smith-Lemli-Opitz syndrome is increased 7-dehydrocholesterol (7DHC). We find increased 7DHC inhibits the ability of zebrafish to control mycobacterial infection by mis-activating an antiviral immune response at the expense of a protective anti-bacterial immune response. Our study suggests the susceptibility to respiratory infections and increased neuroinflammation in Smith-Lemli-Opitz syndrome could be treated by targeting the antiviral protein IRF3.

Systemic lupus erythematosus (SLE) is associated with infection susceptibility and altered innate immune function. Monocyte metabolism is linked to appropriate cytokine release and bacterial containment. We investigated cytokine production and metabolic programming in the monocyte population from SLE patients and healthy controls following lipopolysaccharide (LPS) stimulation. SLE monocytes displayed increased IL-10, TNF, and IL-8 production, with impaired IL-1{beta} induction. Metabolic profiling revealed altered substrate use, with increased glucose dependence and reduced fatty acid and amino acid oxidation after LPS stimulation. SLE patients exhibited reduced numbers of classical monocytes, expansion of intermediate monocytes, and dysregulated subset-specific metabolic reprogramming in response to LPS. This descriptive study provides a cornerstone for (i) understanding infection susceptibility in SLE, (ii) subset-resolved immunometabolic profiling as a tool in autoimmunity, and (iii) developing future metabolic-targeted therapeutic strategies HighlightsO_LIDescriptive mapping shows SLE monocytes are proinflammatory with glucose dependence after LPS C_LIO_LIClassical and intermediate SLE subsets show divergent baseline metabolic preferences versus healthy C_LIO_LISLE subsets display aberrant LPS responses, i.e.. increased glucose and reduced fatty acid oxidation C_LIO_LIThis study provides a cornerstone for subset-resolved immunometabolism in infection susceptibility. C_LI

T cell development in the thymus requires tightly coordinated transcriptional programs that regulate lineage commitment, proliferation and differentiation. While key transcription factors controlling these processes have been extensively characterized, the contribution of the low expressed nuclear receptor Liver Receptor Homolog 1 (LRH-1, Nr5a2) in T cell development remains unexplored. Here, we investigated the role of LRH-1 in thymocyte maturation using an inducible ex vivo deletion system and in vivo Lck-Cre- and CD4-Cre-mediated LRH-1 knockout mouse models. We demonstrate that inducible LRH-1 deletion impairs early thymocyte development, identifying LRH-1 as a critical regulator of the double negative (DN)2/DN3 to DN4 transition. Early Lck-Cre-mediated deletion of LRH-1, but not CD4-Cre-mediated deletion at the double positive stage, resulted in markedly reduced thymic size and cellularity, indicating a stage-specific requirement for LRH-1 during thymopoiesis. Lck-Cre-mediated LRH-1 deletion led to a decreased frequency of mature CD4 T cells in peripheral lymphoid organs, while the remaining mature T cells were predominantly Cre reporter-negative and therefore escaped LRH-1 deletion. CD4 T cells that escaped Cre-mediated LRH-1 deletion exhibited impaired T cell activation marker expression and cytokine secretion. In vivo, these defects resulted in attenuated T cell effector function and compromised regulatory T cell-mediated protection in a T cell transfer model of colitis, indicating impaired effector and regulatory T cell function under (patho)physiological conditions. Collectively, our findings identify LRH-1 as a critical, previously unrecognized regulator of early thymocyte development, and establish its essential role in shaping functional peripheral CD4 T cell-mediated immune responses.

BackgroundNatural killer (NK) cell degranulation is a key immune defense mechanism where exposure to tumor or virus-infected cells triggers the fusion of cytoplasmic granules containing apoptotic proteins, perforin, and granzyme with the cell membrane. This process transiently expresses CD107a on the NK cell surface, and measuring CD107a is a standard method to assess NK cell activity. MethodsWe compared two stimulation protocols differing only in duration (6-hour vs. 18-hour) using K562 target cells to induce NK cell degranulation. Isolated PBMCs without stimulation served as controls to assess spontaneous degranulation. Anti-CD107a-PE antibody was present throughout stimulation in both test and control samples. After stimulation, cells were stained with anti-CD45, anti-CD3, and anti-CD56 and analyzed by flow cytometry. ResultsFor 6 of 7 healthy controls, results from both methods fell within 2 standard deviations. Notably, longer (18-hour) stimulation resulted in lower CD107a expression than the 6-hour assay. Interlaboratory comparisons of two samples showed no significant difference (p>0.05). In a suspected hemophagocytic lymphohistiocytosis (HLH) case, two labs reported similarly reduced CD107a expression (9% and 7%). Inter-day variability was observed in a donor across both time points. The 6-hour assay showed higher sensitivity and specificity than the 18-hour assay. A resting period before ex vivo PBMC assays was found necessary. ConclusionStimulation periods beyond 6 hours are unsuitable for clinical NK degranulation assays. Screening for HLH should include multiple stimulants to improve assay reliability.

The impact of microglia antigen presentation on CNS infiltrating CD8 T cells responses during neurotropic virus infection has been difficult to define. Using Theilers murine encephalomyelitis virus (TMEV) infection of neurons as a model system, our laboratory has previously determined that H-2Db restricted, but not H-2Kb restricted CD8 T cells are required for viral clearance, demonstrating the role of discrete MHC class I alleles. To determine the extent microglia antigen presentation impacts brain-infiltrating CD8 T cells, our laboratory generated novel single MHC class I conditional knockout mice in which H-2Kb or H-2Db can be specifically deactivated in TMEM119+ microglia with tamoxifen administration. During TMEV infection, conditional knockout of H-2Kb in microglia reduced antigen-specific CD8 T cell proliferation in the brain. Meanwhile, mice with deletion of Db in microglia had reduced levels of perforin in antigen-specific CD8 T cells. Furthermore, microglia specific deletion of H-2Db reduced CD8 T cell numbers in the brain and preserved blood-brain barrier (BBB) integrity. Microglial Db restricted antigen presentation was also essential for the reactivation of CD8 tissue resident memory (TRM) cells and BBB integrity during memory recall responses. These findings further our understanding of how brain infiltrating antiviral CD8 T cell responses are impacted by microglia, as well as define how this cellular interaction contributes to BBB disruption during neuroinflammation. These findings also have high significance to our understanding of how microglia impact CD8 TRM cell populations that reside in the brain long after virus infection is cleared. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/722741v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@9302a9org.highwire.dtl.DTLVardef@193b5f4org.highwire.dtl.DTLVardef@8eb036org.highwire.dtl.DTLVardef@1d2cd6a_HPS_FORMAT_FIGEXP M_FIG C_FIG

Circulating proteins have been widely investigated as potential biomarkers in multiple sclerosis (MS), yet findings across studies are often inconsistent, likely reflecting differences in disease stage, treatment exposure, and cohort composition. Studying individuals at elevated risk of MS prior to disease onset offers a unique opportunity to identify immune alterations that precede clinical disease while minimizing confounders. Here, we investigated whether alterations in six previously MS-associated biomarkers are detectable and associate to underlying genetic susceptibility in two independent sample collections comprising people with MS (pwMS), healthy controls, and asymptomatic first-degree relatives of pwMS from the Genes & Environment in MS (GEMS) study cohort. The panel, representing complementary axes of MS immunopathology, included granzyme A (GZMA), MER tyrosine kinase (MERTK), interleukin-2 receptor alpha (IL2RA), osteopontin (SPP1), CD30 (TNFRSF8), and chitinase-3-like protein 1 (CHI3L1). None of the proteins demonstrated associations with MS. A composite score constructed from externally derived effect estimates was not associated with MS status in either collection or in meta-analysis. Among asymptomatic first-degree relatives, the composite score was not significantly associated with group status. In contrast, an inverse correlation between SPP1 and the MS genetic risk score among GEMS participants was found ({beta} = -0.246, p = 0.001). Together, these findings suggest that several circulating proteins recently proposed as MS biomarkers are not robust tools to distinguish MS from healthy individuals. However, SPP1 levels are highlighted for further evaluation among at-risk individuals, and further work is needed to determine whether circulating immune signatures can capture the earliest stages of MS in at-risk individuals.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterised by sustained type I interferon signalling and widespread immune dysregulation. Low-density neutrophils (LDNs) are expanded in SLE and display pro-inflammatory and tissue-damaging properties. However, their metabolic phenotype remains poorly defined. Here, we performed a comprehensive metabolic characterisation of circulating LDNs and normal-density neutrophils (NDNs) from patients with SLE and matched healthy individuals (HC). Neutrophil subsets were isolated from peripheral blood of SLE patients and HC donors using a two-step protocol of negative selection and Percoll density centrifugation. Immunophenotyping phenotype was carried out by flow cytometry to assess phenotypic expression of common neutrophil markers CD15, CD16, CD10, CD66b, CD62L, MPO, and IL-1{beta}. Bioenergetic profiling of LDNs and NDNs was performed in situ using the Seahorse MitoStress test to measure oxygen consumption rate (OCR) and extracellular acidification rate (ECAR). Metabolic flexibility and phenotypic alterations were assessed in LDNs and NDNs following inhibiting mitochondrial metabolism with oligomycin and glycolysis with 2DG. We found that SLE LDNs exhibit an immature phenotype compared with autologous and healthy NDNs, as determined transcriptionally by C/EBP{varepsilon} and by surface protein expression levels of CD10. Both LDNs and NDNs from SLEDAI[≥]4 patients demonstrated significantly elevated ECAR relative to HC neutrophils. Further, SLE LDNs displayed enhanced metabolic flexibility, with the capacity to switch towards a glycolytic phenotype under metabolic stress conditions. Inhibition of glycolysis altered the inflammatory and maturation-associated phenotype of both SLE neutrophil subsets, indicating a direct link between cellular metabolism and pathogenic neutrophil function. Collectively, these findings identify fundamental metabolic alterations in SLE neutrophil subsets and support neutrophil immunometabolism as a potential therapeutic target in SLE.

BackgroundThyroid Eye Disease (TED) is an autoimmune orbital disorder driven by pathogenic T-cell subsets, including T-helper 1 (Th1) and follicular helper T (Tfh) cells, which sustain orbital inflammation and thyroid-stimulating immunoglobulin (TSI) production. Selenium supplementation has demonstrated clinical benefit in mild TED, yet its immunological mechanisms remain poorly defined. MethodsA murine TED model was established in female BALB/c mice via TSHR plasmid immunisation. Animals maintained on a low-selenium diet (0.07 ppm) received sodium selenite supplementation at 0.2 mg/kg/day. Orbital pathology was assessed by immunohistochemistry, H&E and Massons Trichrome staining. T-cell subset abundance was quantified by flow cytometry, and serum T4, TRAb, and IL-21 levels were measured by ELISA. In vitro dose-response experiments examined the effects of selenium on Tfh cell viability, IL-21 production, apoptosis, and ferroptosis. ResultsSelenium supplementation reduced CD3 T-cell orbital infiltration, collagen fibrosis, and serum T4 and TRAb levels in TSHR-immunised mice. Flow cytometry revealed significant reductions in Tfh and Th1 cell abundance, with Th17 cells unaffected. Serum IL-21 and B-cell abundance were also markedly reduced in vivo. In vitro, selenium exhibited a biphasic, dose-dependent effect on Tfh cells: low concentrations maintained viability and IL-21 production, while higher concentrations induced ferroptosis and apoptosis. ConclusionsSelenium modulates pathogenic T-cell responses in TED, most prominently suppressing the Tfh compartment and attenuating the Tfh-B cell-autoantibody axis via ferroptosis and apoptosis. These findings suggest a mechanistic framework for the clinical benefit of selenium in mild TED and highlight the importance of dose selection within its narrow therapeutic window.

Innate immunity and innate immune cell death provide a critical first line of defense against disease. However, excess cell death leads to pathological inflammation. ZBP1 is an innate immune sensor that is central to this balance between defense and inflammation as a driver of inflammatory lytic cell death, PANoptosis. Activation of ZBP1-dependent PANoptosis downstream of diverse triggers has roles in both host defense and disease pathology, making ZBP1 an attractive therapeutic target. Therefore, understanding the distinct roles of ZBP1 in different cell types, organ systems, and tissues is critical to identify therapeutic strategies. Although ZBP1 regulates PANoptosis in multiple cell types, there are limited tools to interrogate its function in a cell type-specific manner. Here, we report the generation of a Zbp1-floxed mouse line (Zbp1fl/fl) for investigation of ZBP1 in distinct cell populations. We crossed Zbp1fl/fl mice to LysMcre mice to selectively deplete Zbp1 from the myeloid compartment, which did not alter immune homeostasis. Bone marrow-derived macrophages (BMDMs) from Zbp1fl/fl mice had normal ZBP1 expression and PANoptosis activation, while those from Zbp1fl/flLysMcre mice exhibited markedly reduced ZBP1 expression and were biochemically and functionally protected from ZBP1-driven PANoptosis; these effects were validated using known triggers of the ZBP1-PANoptosome--IAV, nuclear export inhibition plus IFN, and ethanol. These findings demonstrate this new Zbp1fl/fl mouse as a versatile tool that can be utilized with a variety of Cre-drivers to study ZBP1 in a wide array of distinct cell types. Given the critical role of ZBP1 in disease, this tool will inform the development of therapeutic strategies.

Orientia tsutsugamushi (Ot) is an obligately intracellular bacterium that causes scrub typhus, a potentially severe infectious disease characterized by systemic inflammation and multiorgan dysfunction. We recently reported a protective role for IFN-{gamma} signaling in host defense against Ot infection; however, the underlying mechanisms remain obscure. Inducible nitric oxide synthase (iNOS, encoded by Nos2) is a key antimicrobial effector induced downstream of IFN-{gamma} signaling. Here, we used transgenic mouse models to further investigate the biological functions of iNOS. We first revealed the requirement of iNOS for the restriction of Ot growth in cultured bone marrow-derived macrophages. Using an intradermal mouse model, we found that while tissues of Nos2-/- and wild-type mice exhibited comparable bacterial burdens during acute infection phases, Nos2-/- mice developed eschar-like lesions similar to those observed in Ifngr1-/- mice, indicating a critical role for the IFN-{gamma}/iNOS axis in regulating skin pathology in scrub typhus. Notably, Nos2-/- mice displayed impaired bacterial clearance during the recovery phase (day 42), with persistent bacterial burdens in multiple organs accompanied by sustained immune activation and elevated inflammatory responses. Histopathological and biochemical analyses further revealed increased tissue damage and dysregulated physiological homeostasis in Nos2-/- mice during recovery. Mechanistically, iNOS deficiency resulted in heightened myeloid cell activation and prolonged expression of proinflammatory mediators, suggesting a dual contribution of iNOS in both antimicrobial defense and inflammation resolution. Collectively, these findings provide new insight into IFN-{gamma}-mediated defense mechanisms and imply the distinct roles of iNOS during different stages of scrub typhus. Author summaryScrub typhus is a potentially severe infectious disease caused by the bacterium Orientia tsutsugamushi (Ot), which is transmitted to humans through the bite of infected mites. Despite its global impact and expanding geographic distribution, the immune mechanisms that protect against this infection remain incompletely understood. In this study, we examined the role of inducible nitric oxide synthase (iNOS), an immune effector molecule that helps the host control infection. Using mouse models, we found that iNOS plays dual and stage-specific roles during Ot infection. Mice lacking iNOS developed dysregulated immune homeostasis during acute infection and exhibited skin lesions resembling the eschars observed in some patients with scrub typhus. In addition, these mice showed delayed bacterial clearance, prolonged inflammation, and increased tissue damage during the recovery phase. Our findings indicate that iNOS contributes not only to host antimicrobial defense but also to the control of excessive inflammation following infection. These results provide new insight into host defense mechanisms in scrub typhus and may help inform future therapeutic or preventive strategies.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID are complex chronic conditions that often follow infectious triggers with overlapping clinical features but poorly defined pathophysiological relationships. This study aimed to identify disease-specific immune signatures through multiparameter immunophenotyping of monocytes, dendritic cells, and T-cell subsets. A total of 207 participants were included (ME/CFS: n = 103; long COVID: n = 63; healthy controls: n = 41). Peripheral blood mononuclear cells were analyzed using multiparameter flow cytometry. Statistical analyses included non-parametric testing, age-adjusted ANCOVA, correlation network analysis, and principal component analysis (PCA). Long COVID was characterized by increased M2-like monocyte polarization, elevated CD80 expression across monocyte subsets, expansion of dendritic cells, and reduced expression of activation markers, indicating persistent immune activation with features of immune exhaustion. In contrast, ME/CFS exhibited reduced costimulatory molecule expression, impaired CCR7-mediated immune cell trafficking, and less coordinated activation patterns, consistent with a state of immune suppression. Correlation network analysis revealed more extensive and integrated immune interactions in long COVID, while PCA identified distinct immunophenotypic components and enabled moderate discrimination between the two conditions. These findings demonstrate that ME/CFS and long COVID are characterized by distinct immune profiles, supporting the concept of divergent immunopathological mechanisms. The identified signatures may contribute to biomarker development and guide targeted therapeutic approaches.

Francisella tularensis is a Gram-negative bacterium that causes tularemia, a fatal zoonotic disease. F. tularensis has been used in the bioweapon programs of several countries. Its potential use as a bioterrorism agent led the CDC to classify F. tularensis as a Tier 1 Select Agent. The cytosolic sensor absent in melanoma 2 (Aim2) detects double-stranded DNA in the cytosol of infected cells and subsequently assembles a multiprotein complex known as the inflammasome. Inflammasome activation drives the secretion of IL-1{beta} and IL-18, key proinflammatory cytokines required for controlling F. tularensis infection. Prior studies have shown that F. tularensis actively suppresses Aim2 inflammasome activation; however, the underlying mechanism remains unknown. We hypothesized that F. tularensis suppresses Aim2-mediated responses by modulating the intracellular redox environment. We utilized an F. tularensis mutant lacking OxyR ({Delta}oxyR), a transcriptional regulator that controls the expression of major antioxidant enzymes. Our results show that macrophages infected with the {Delta}oxyR mutant exhibit significantly higher levels of Aim2-dependent Caspase-1 and IL-1{beta} than those infected with wild-type bacteria. The expression of interferon regulatory factor 1 and the guanylate-binding proteins GBP2 and GBP5, upstream signaling components of the Aim2 inflammasome, is markedly higher in {Delta}oxyR-infected macrophages than in controls. These changes were absent in {Delta}oxyR-infected NADPH oxidase-deficient macrophages, which are unable to generate reactive oxygen species. Collectively, these findings demonstrate that macrophage redox environment plays a key role in activating signaling components required for Aim2 inflammasome activation. This work advances our understanding of how F. tularensis-encoded factors subvert host innate immune defenses.

{gamma}{delta} T cells provide mucosal defense against infection while also contributing to tissue repair. However, data regarding the effect of the human lung environment on {gamma}{delta} T cell functionality remains limited. To address whether lung inflammation impacts {gamma}{delta} T cell functionality, we analyzed lung and matched hilar lymph node (LN) tissue from deceased donors and patients with interstitial lung disease (ILD). We performed high-parameter spectral flow cytometry to examine the expression pattern of phenotypic biomarkers and assess ex vivo function. We identified lung-specific enrichment of {gamma}{delta} T cells with an effector memory phenotype relative to matched regional LN. We then used an ex vivo stimulation approach to interrogate the capacity to protect against infection (granzyme B [GzmB], interferon-{gamma} [IFN{gamma}] and tumor necrosis factor [TNF]) and promote epithelial cell proliferation (amphiregulin [AREG]). We found that {gamma}{delta} T cells in lung and LN from deceased donors had similar functional properties. While {gamma}{delta} T cell populations from ILD lungs largely maintained cytokine production capacity, expression was diminished relative to LN counterparts. Importantly, lung {gamma}{delta} T cells maintained polyfunctional GzmB, IFN{gamma} and TNF expression across cohorts. Overall, we report human lung {gamma}{delta} T cells are regionally distinct with conserved functionality in a fibrotic environment.