Mucosal Immunology

CD4 T cells are essential for protective immunity against Chlamydia in the female reproductive tract (FRT), yet the characteristics of protective mucosal effector CD4 T cells remain poorly defined. We previously identified the transcription factor BHLHE40 as a key regulator of polyfunctional effector CD4 T cell differentiation during Chlamydia infection. Here, we identify the chemokine receptor CXCR6 as a marker of these protective T cells. Following intravaginal Chlamydia muridarum infection, Bhlhe40-deficient mice exhibited reduced frequencies of CXCR6 CD4 T cells that correlated with impaired bacterial control. CXCR6 expression on T cells was associated with loss of stem-like features and acquisition of an effector phenotype. Compared with CXCR6- cells, CXCR6 CD4 T cells displayed enhanced proliferation and polyfunctionality by co-producing cytokines IFN-{gamma}, IL-17A, and GM-CSF. Although CXCR6 was dispensable for CD4 T cell homing to the FRT, it promoted localization to the infected epithelium and the emerging memory lymphoid clusters. Importantly, depletion of CXCR6 CD4 T cells reduced polyfunctional effectors and impaired bacterial clearance. Collectively, these findings identify CXCR6 as a marker of protective polyfunctional CD4 T cells and implicate CXCR6-dependent tissue positioning as a key component of effective mucosal immunity, highlighting CXCR6 as a potential biomarker for Chlamydia vaccine development.

Inflammatory bowel disease (IBD) arises from dysregulated crosstalk between innate immune, adaptive immune, and stromal compartments, yet the compartment-specific mechanisms driving tissue injury and tumorigenesis remain incompletely defined. To address this gap, we used conditional knockout and overexpression mouse models together with human IBD biopsy analysis to dissect the compartment-specific roles of lamin A/C in intestinal inflammation and colitis-associated tumorigenesis. Pan-hematopoietic lamin A/C deletion attenuated acute dextran sulfate sodium (DSS)-induced colitis. Myeloid-specific lamin A/C deletion ameliorated chronic colitis and was associated with altered dendritic cell (DC) programs, enhanced regulatory T cell (Treg) responses, and reduced effector T cell activation. Adoptive transfer of lamin A/C-deficient bone marrow-derived DCs recapitulated this reduced-damage phenotype in DSS colitis, while proteomic profiling revealed reduced antigen-processing and inflammatory programs together with enhanced metabolic and mucosal defense pathways. T cell-specific lamin A/C deletion reduced the Th1/Treg ratio and limited tumor development by suppressing chronic inflammation, whereas T cell-specific lamin A/C overexpression promoted severe Th1-skewed pathology, sustained intestinal inflammation, and increased colitis-associated tumor burden. Stromal fibroblast-specific lamin A/C deletion generated a tissue-protective niche characterized by enhanced epithelial barrier gene expression, regulatory cytokine production, and remodeling of the local immune milieu. Human IBD biopsies revealed compartment-specific lamin A/C alterations consistent with the murine findings. In lamina propria CD3+; T cells, lamin A/C levels were blunted in IBD and associated with local histological severity rather than IBD diagnosis, whereas epithelial lamin A/C showed a steeper crypt-axis spatial gradient in a Crohn's disease-specific pattern. Together, these findings identify lamin A/C as a cell-type- and context-dependent regulator of intestinal inflammation and tumorigenesis.

Despite the superior efficacy of high-dose influenza vaccines, over one-third of older adults fail to respond. Yet, the mechanisms underlying this impaired vaccine responsiveness remain poorly understood. Here, we performed longitudinal profiling of older adults (n=60) receiving high-dose influenza vaccination to identify immune programs associated with vaccine responsiveness. Strong responders exhibited a primed baseline immune state characterized by elevated plasma cytokines and chemokines, followed by enhanced IFN-{gamma} responses and coordinated transcriptional and epigenetic activation of cDC2 cells at day 1. By day 7, CD4+ T-cell trajectories diverged: strong responders preferentially expanded influenza-specific activated cTfh1 (CXCR5+ CXCR3+ ICOS+ CD38+) and influenza-specific Th10 (CXCR5- CXCR3+ PD1+ IL10+) cells, whereas weak responders expanded regulatory cTfr (CXCR5+ FOXP3+) cells. Th10 expansion correlated with plasmablast and antibody responses and was independently validated in a larger influenza vaccination cohort, including younger adults. Functionally, Th10 cells promoted memory B-cell differentiation into plasmablasts and production of influenza-specific IgGs. TCR analyses revealed minimal clonal overlap between Th10 and cTfh1 cells. Together, these findings identify divergent helper and regulatory CD4+ T cell programs associated with vaccine responsiveness and establish Th10 cells as a previously unrecognized component of vaccine-induced humoral immunity.

Elastin degradation during chronic lung inflammation generates elastin peptides (EPs) with immunomodulatory properties. Because elastin is abundant in the lung, its breakdown in diseases such as chronic obstructive pulmonary disease (COPD) and asthma produces high EPs levels that may influence local immune responses. Here, we investigated the impact of EPs on group 2 innate lymphoid cells (ILC2) using mouse models of EP-induced emphysema and house dust mite (HDM)-induced asthma. EPs instillation reduced lung ILC2 numbers without affecting Th2 cells. In patients with COPD, we observed decreased CCL20 expression in lung immune cells and an inverse correlation between serum CCL20 levels and clinical indicators of elevated EPs burden. We also showed that EPs instillation during HDM-induced lung inflammation directly decreased CCL20 expression. These findings identify EPs as regulators of ILC2 trafficking through CCL20 downregulation, revealing a direct link between extracellular matrix (ECM) degradation and the chemokine networks orchestrating type 2 immunity. One Sentence SummaryElastin-derived peptides reshape type 2 immunity by blocking CCL20-driven ILC2 recruitment during lung inflammation.

Background: Reproductive tract infections (RTIs) and bacterial vaginosis (BV) are major causes of genital inflammation and reproductive morbidity, yet often remain undetected under syndromic management. We evaluated cervicovaginal cytokine signatures associated with RTIs and vaginal dysbiosis in women from South Africa, Madagascar, and Zimbabwe. Methods: Vaginal swabs from 676 non-pregnant, sexually-active women (18 - 35 years) were tested for Chlamydia trachomatis (CT), Neisseria gonorrhoeae (NG), Trichomonas vaginalis (TV), Mycoplasma genitalium (MG), Candida spp., and BV by PCR and Nugent scoring. Cervicovaginal IL-1a, IL-1b and IP-10 concentrations were measured by ELISA, and associations with RTIs and vaginal dysbiosis were assessed using multivariable regression and population attribution fraction analyses. Results: BV (Nugent 7 -10) was the most prevalent (50.4%) and dominant contributor to elevated IL-1a and IL-1b, accounting for >60% of women with high cytokine levels. Intermediate vaginal microbiota (Nugent 4 - 6) showed similar inflammatory profiles and, with BV, was associated with reduced IP-10. NG was independently associated with elevated IL-1a and IL-1b, CT with elevated IL-1b and IP-10, TV with elevated IP-10, Candida spp. with elevations in all cytokines, while MG showed no independent associations. Most RTIs and vaginal dysbiosis were asymptomatic, with similar inflammatory profiles regardless of symptoms. Despite variation in baseline cytokine concentrations, infection-associated inflammatory signatures were consistent across countries. Conclusions: RTIs and vaginal dysbiosis elicited consistent inflammatory signatures across countries, with BV and intermediate microbiota driving much of the inflammatory burden. Their frequent occurrence in asymptomatic women highlights the potential of host-response biomarkers to identify otherwise undetected genital inflammation.

Pneumonia is a leading cause of death globally and disproportionately affects children in lower- and middle-income countries. To explore microbial and immune correlates of disease and death, we performed metagenomic sequencing of upper respiratory tract (URT) microbiome in 309 children in Mali with pneumonia and 150 age- and season- and site-matched controls. We show that the URT microbiome matures throughout early life and is influenced by breastfeeding. URT microbiome maturation was disrupted during pneumonia resulting in loss of commensal species and expansion of pathobionts, which was linked to disease severity and death. Analysis of serum antibody levels revealed that low levels of passively acquired antibody from mothers, deficient antibody responses to RSV, and persistent autoantibody to cytokines were associated with pneumonia mortality in an age-dependent manner. These findings underscore the complex nature of pneumonia and identify microbial and immune factors for risk stratification and therapeutic interventions in pediatric pneumonia.

Langerhans cells (LC) are specialized antigen-presenting cells that form a dense immune surveillance network within the oral epithelium. There, they continuously interact with epithelial cells and the resident microbiota to maintain mucosal homeostasis. A defining feature of LC is their highly dendritic morphology, which enables efficient sampling of the environment at barrier surfaces. Although E-cadherin-mediated adhesion has been implicated in LC-epithelial cell interactions, its role in oral LC biology and periodontal immune homeostasis remains elusive. Here, we investigated the function of E-cadherin on oral LC using CD11c-specific E-cadherin-deficient (CD11c-EcadDEL) mice. Loss of E-cadherin profoundly altered LC morphology throughout the oral mucosa, resulting in reduced dendrite formation and impaired dendrite extension towards the epithelial surface, thereby disrupting interaction with the oral microbiota. While the total number of LC remained unchanged, E-cadherin deficiency significantly altered the relative distribution of LC subsets, characterized by reduced LC1 and increased LC2 populations. E-cadherin-deficiency was associated with pronounced oral dysbiosis, characterized by increased bacterial burden and microbial diversity, as well as a shift away from the commensal-dominated community, particularly through the loss of protective lactobacilli. Transcriptome analysis of gingival tissue revealed inflammatory reprogramming marked by enrichment of NF-{kappa}B, TNF, IL-17, Toll-like receptor, and MAPK signaling pathways. Consistently, CD11c-EcadDEL mice exhibited increased IL-17A production in the gingiva, expansion of {beta} and {gamma}{delta} T cells, spontaneous age-dependent alveolar bone loss, and exacerbated inflammatory bone destruction in a model of ligature-induced periodontitis. In summary, our findings reveal that E-cadherin preserves oral LC dendrite organization and microbiota-dependent immune homeostasis, thereby limiting dysbiosis-driven inflammation and periodontal bone loss.

Biological sex can profoundly influence the susceptibility to infectious diseases, yet the mechanisms behind the sex-dependent protective immunity against tuberculosis (TB) remain poorly understood. Here we show that sexually divergent immunity during chronic Mycobacterium tuberculosis (Mtb) infection is governed by both intrinsic T cell programming and pulmonary immune spatial organization. Using the Four Core Genotype (FCG) mouse model, adoptive cell transfer, pathway-specific blockade and B cell depletion, we demonstrate that CD4 T cells from gonadal females (XXF), but not XX males (XXM), confer enhanced protection to susceptible XY male recipients, independently of sex chromosome complement. Female-derived CD4 T cells reduce Mtb burdens while promoting pulmonary Bcl6 CD4 T cell responses and limiting neutrophilic inflammation. Mechanistically, blockade of CXCR3 or CD40L abrogates female-associated protection, with CD40L signaling additionally required to maintain organized pulmonary B cell structures. Although depletion of conventional B-2 B cells did not impair bacterial control, it disrupted tertiary lymphoid organization and revealed striking sex-specific functions of pulmonary B cells. Loss of B cell follicles (BCFs) primarily remodeled adaptive T cell responses in females, whereas in males it drove inflammatory myeloid activation, exaggerated neutrophil recruitment and widespread neutrophil extracellular trap (NET) formation. Together, these findings identify two complementary layers of sex-dependent immune regulation during TB: intrinsic programming of protective female CD4 T cells, and B cell-dependent spatial organization that coordinates adaptive immunity in females while restraining pathological inflammation in males. These findings establish immune tissue organization as a key determinant of the sexually dimorphic host defense during chronic TB.

Receptor activator of NF{kappa}B ligand (RANKL) is important for bone metabolism, but also modulates immune processes. We showed that mast cells (MCs) are involved in RANKL regulation, but the importance of MC-derived RANKL in skin inflammation has not yet been investigated. In contact hypersensitivity (CHS), the absence of MC-derived RANKL led to reduced skin inflammation due to impaired leukocyte infiltration and blood lymphopenia. Surprisingly, we observed a massive hyperplasia of the distant inguinal lymph nodes in the absence of MC-RANKL. Using adoptive transfers, flow cytometry and whole-mount 3D imaging, we demonstrated that this was not caused by structural maladaptation, but rather by the inability of lymphocytes to exit in a timely manner. Importantly, RANKL deletion in skin MCs only replicated the effect of LN hyperplasia and blood lymphopenia. Moreover, MCs were involved in serum sphingosine-1-phosphate (S1P) regulation during sensitization and challenge. Intravascular administration of S1P restored timely lymphocyte egress, demonstrating a MC-induced organ-spanning RANKL-S1P axis. Consequently, peripheral skin MC-derived RANKL is essential for the timely lymphocyte egress from distant LNs, which may have important implications for the targeted treatment of inflammatory skin diseases.

Chronic infections require mechanisms that limit tissue damage while preserving pathogen control, yet the contribution of regulatory T (Treg) cells to this balance remains unclear. In this study, we characterized Treg cell responses during a chronic parasitic infection using experimental Trypanosoma cruzi infection as a model of persistent low-level parasitism and chronic tissue inflammation. We found that, although Treg cell numbers decline in the spleen, they accumulate in parasite-affected tissues such as skeletal muscle, where they adopt a combined Th1-associated and tissue-repair program. Systemic Treg cell depletion had limited impact on immune and disease-associated parameters, whereas local depletion in skeletal muscle exacerbated tissue damage and increased parasite burden. Moreover, transient systemic perturbation of Treg cells during the acute phase impaired their long-term accumulation in skeletal muscle, resulting in increased tissue damage and parasite burden during chronic infection. Additionally, accumulation of reparative Treg cells in skeletal muscle was impaired in the absence of ST2. Together, these findings identify a tissue-adapted Treg cell population that integrates inflammatory and reparative programs to preserve skeletal muscle integrity during chronic parasitic infection.

Background Growing evidence suggests that the gut microbiome influences nasal and ocular allergic inflammation through gut-mucosal immune interactions. Yet, its association with Allergic rhinitis (AR) and allergic eye symptoms (AES) remains incompletely understood in large population-based cohorts. Objective To examine associations between the gut microbiome and self-reported AR and AES in Finnish adults. Methods Shallow metagenomic sequencing was performed on stool samples from a population-based cohort (FINRISK02; n = 7,231). Microbial taxonomic and functional profiles were compared between individuals with AR (n = 1,950), AES (n = 1,554), combined allergies (AR and/or AES; n = 2,305), and controls without reported symptoms (n = 3,175). Results Allergic groups exhibited lower microbial richness and phylogenetic diversity than controls. Shared microbial and functional signatures were observed across AR and AES, consistent with their high co-occurrence (N = 1,199). Compared with controls, allergic groups showed enrichment of 17 bacterial species, predominantly from the Clostridia class, including taxa previously associated with asthma, chronic obstructive pulmonary disease, and atopic dermatitis. Allergic individuals also exhibited enrichment of pathways related to mucosal carbohydrate processing, shikimate metabolism, histidine turnover, and broader amino acid metabolism. Concurrent enrichment of histidine biosynthesis and degradation suggested altered microbial histidine metabolism. Conclusions Adult allergic symptoms are associated with gut microbiome taxonomic and functional alterations linked to mucosal barrier function and immune-related metabolism, supporting a shared gut-mucosal immune axis across allergic phenotypes.

Chronic obstructive pulmonary disease (COPD) is a progressive inflammatory airway disease in which impaired mucosal barrier function may increase susceptibility to aspirated oral microbial products. Periodontal disease has been associated with COPD development and exacerbation, but the epithelial mechanisms linking periodontal pathogens to pulmonary immune remodeling remain unclear. Here, we investigated whether gingipain-containing Porphyromonas gingivalis culture supernatant (PCS) promotes {gamma}{delta} T-cell-associated inflammation in COPD-like airways. Repeated intratracheal administration of PCS to {beta}ENaC-transgenic mice induced airway-centered immune cell accumulation and increased {gamma}{delta} TCR-positive cell accumulation, together with elevated expression of the {gamma}{delta} T-cell-associated cytokines Ifng and Il17a. PCS also increased pulmonary Ccl20 and Ccr6 expression, whereas epithelial alarmin-related genes and M2 macrophage-associated responses were not induced in parallel. In ENaC-overexpressing human airway epithelial cells, PCS induced CCL20 and F2RL1, the gene encoding protease-activated receptor 2 (PAR-2), and reduced the N-terminal PAR-2 signal, consistent with proteolytic receptor cleavage. Direct PAR-2 activation reproduced CCL20 induction, whereas pharmacological PAR-2 inhibition suppressed PCS-induced CCL20 expression. In contrast, PAR-1 inhibition or LPS neutralization with polymyxin B did not suppress this response. These findings support a mucosal epithelial protease-sensing model in which gingipain-containing P. gingivalis products activate PAR-2-dependent CCL20 production in airway epithelial cells and are associated with CCR6-linked {gamma}{delta} T-cell accumulation in COPD-like airways.

Background Early-life respiratory syncytial virus (RSV) infection is associated with childhood recurrent wheeze or asthma (RW/A), but causality and shared genetic liability remain unclear. Methods We combined Finnish nationwide registries and Nordic genetic cohorts. First, in 965 312 Finnish children born between 1998 and 2014, we defined severe RSV as RSV hospitalisation before age 1 year, and recurrent wheezing or asthma (RW/A) as inhaled medication reimbursement between ages 1 and 7 years, and compared medication and eosinophil trajectories by RSV history. Second, we assessed familial confounding in 527 776 full siblings and 15 667 RW/A-discordant pairs. Third, we performed a genome-wide association study (GWAS) of RSV susceptibility with meta-analysis across six Nordic cohorts (3 107 cases, 92 031 controls) and two-sample Mendelian randomisation (2SMR) using 155 asthma-associated variants. Findings RSV-associated RW/A showed higher inhaled medication use at ages 1-2 years but lower use after age 4, and lower mean blood eosinophils (0.34 vs 0.39*10e9/L; p=0.003) than RW/A without RSV hospitalisation. In RW/A-discordant sibling pairs, RSV hospitalisation was associated with RW/A (OR 2.8; 95% CI 2.4-3.2), while unaffected siblings also had elevated RW/A prevalence. GWAS identified an RSV association at APBB1IP (rs787036; beta=0.209; p=8.80*10e-9). 2SMR provided no evidence that asthma genetic liability influenced RSV susceptibility. Interpretation The RSV-asthma association is unlikely to be explained by shared genetic or environmental factors, and RSV-associated RW/A shows a distinct trajectory. These findings help prioritise long-term outcomes for RSV prevention trials and monitoring. Funding: Paivikki and Sakari Sohlberg Foundation, Foundation for Pediatric Research, Sigrid Juselius Foundation, Orion Research Foundation, the Research Council of Norway.

Cannabinoid receptor 2 (CB2R) is highly expressed on immune cells, but its role in T cell metabolism remains unclear. Here, we show that CB2R activation rapidly increases glucose uptake in human Jurkat T cells and drives a broader metabolic reprogramming away from glycolysis toward oxidative metabolism and the pentose phosphate pathway. Pharmacological CB2R activation increased mitochondrial mass, spare respiratory capacity, proton leak, and NADPH production, while CB2R inverse agonism produced the opposite effects. These metabolic changes were accompanied by upregulation of key pentose phosphate pathway enzymes, including GALT and TALDO1, and were abolished in CNR2-deficient cells, confirming receptor dependence. In primary human lamina propria mononuclear cells, CB2R signalling also influenced memory and gut-homing-associated T cell phenotypes, including integrin 4{beta}7 expression. Together, these findings identify CB2R as a regulator of T cell bioenergetics and suggest that cannabinoid signalling may promote metabolic states linked to memory and tissue-homing functions in chronic intestinal inflammation.

Antibiotics (ABXs) represent the current standard of care for treating Clostridioides difficile infection (CDI). Paradoxically, ABX-induced dysbiosis is the primary risk factor for CDI, as disruption of the colonic microbial ecosystem creates an opportunity for C. difficile colonization. Given that ABXs can also alter immune responses, we investigated whether ABXs prime the colonic immune milieu for CDI susceptibility. Here, we implicate ABXs in driving CDI severity through the emergence of pathogenic CCR5-reliant immune populations in the mouse colon. High-throughput immune cell profiling revealed that ABXs shift the colonic immune compartment toward a CCR5-associated type I immunity signature, marked by an expansion of CCR5+ ILC1s and CCR5+ Th1 cells. A partial genetic deletion of CCR5 reversed CDI severity, alleviating colonic inflammation and improving survival. Pharmacological inhibition of the CCL3/4/5-CCR5 circuit also recapitulated these favorable disease outcomes, which we attribute to reduced colonic CCR5+ ILC1, CCR5+ Th1, and CCR5+ CD8 T cell populations during CDI. Together, our findings extend beyond dysbiosis as the canonical CDI risk factor and establish ABX-induced immune imbalance as an underappreciated determinant of CDI susceptibility.

Recognition of infected macrophages by CD4+ T cells is essential to immune protection against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). However, not all infected macrophage subsets successfully elicit T cell activation. We recently discovered that M2-like macrophages fail to efficiently activate memory CD4+ T cells when infected with Mtb, yet successfully elicit T cell activation when loaded with peptides, {gamma}-irradiated bacteria, or Mtb whole cell lysate. Since the mechanisms underlying CD4+ T cell evasion by infected M2 but not M1-like macrophages remain underexplored, we sought to determine the genes and pathways unique to Mtb infection of M2-like cells, including alveolar macrophages. RNA sequencing of human macrophages infected with virulent Mtb identified enrichment of IL-10 and type I interferon (IFN) signaling genes, including IL10RA and HERC5, respectively, in infected M2-like monocyte-derived and alveolar macrophages. However, genes involved in MHC-II trafficking, such as AP1M2, were higher in infected M1-like macrophages. In complementary experiments using fluorescence microscopy and flow cytometry, we observed impaired trafficking of newly synthesized MHC-II to the plasma membrane of Mtb-infected M2-like macrophages despite high total surface MHC-II levels. Neutralization of IL-10 or knockdown of HERC5 restored MHC-II trafficking to the cell surface among infected M2-like macrophages and significantly enhanced activation of memory CD4+ T cells in an MHC-II-dependent manner. These findings identify coordinated IL-10 and type I IFN signaling as key mechanisms that restrict MHC-II trafficking to the plasma membrane in Mtb-infected M2-like macrophages, thereby limiting antigen presentation and CD4+ T cell activation. We propose that host-directed therapies targeting these pathways in infected alveolar macrophages will facilitate T cell recognition for the prevention or treatment of active TB. Author SummaryRecognition of infected macrophages by CD4+ T cells is essential to immune protection against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). However, not all infected macrophage subsets successfully elicit T cell activation. We recently discovered that M2-like macrophages fail to efficiently activate memory CD4+ T cells when infected with Mtb, yet they successfully elicit T cell activation when treated with peptides, {gamma}-irradiated bacteria, or Mtb whole cell lysate. In this study, we identified genes and pathways uniquely upregulated in Mtb-infected M2-like macrophages that are linked to inefficient CD4+ T cell activation, including IL-10 signaling and type I interferon (IFN) pathways. These pathways were linked to reduced MHC-II trafficking to the plasma membrane in Mtb-infected M2-like macrophages. Neutralization of IL-10 or knockdown of HERC5 restored MHC-II trafficking and augmented memory CD4+ T cell activation. Our study demonstrates that IL-10 signaling and type I IFN pathways play detrimental roles in macrophages during Mtb infection, impairing MHC-II trafficking and CD4+ T cell activation. Since lung-resident alveolar macrophages express a dominant M2-like phenotype, these findings suggest that targeting IL-10 and type I IFN signaling may offer a strategy to enhance CD4+ T cell-mediated immunity and improve TB outcomes.

Early control of viral infection is thought to rely on pattern-recognition receptors (PRRs) that induce interferons (IFNs) and leukocyte recruitment, but how distinct PRRs coordinate mucosal antiviral defense remains unclear. We show that both the DNA-sensing cGAS/STING pathway and the RNA-sensing RLR/MAVS pathway are required for protection upon genital herpes simplex virus type 2 (HSV-2) infection. cGAS deficiency increased infection-induced pathology in both epithelial and submucosal compartments, whereas MAVS deficiency primarily affected the epithelium. Spatial proteomics and regional transcriptomics revealed that cGAS was essential for early epithelial TBK1 activation, expression of IFN-stimulated genes and recruitment and activation of myeloid and lymphoid cells to the epithelium. While MAVS was essential for full TBK1 activation it had limited impact on the induced IFN response. However, MAVS sustained basal epithelial expression of the antiviral factors IFITM1 and 3, which exert antiviral activity against HSV-2. Notably, cGAS deficiency impaired submucosal IFN responses and enabled viral spread into this tissue, enabling infection of intervening neurons and dissemination to the central nervous system. These findings define coordinated, compartment-specific innate defense against infections.

The low efficacy of Bacille Calmette-Guerin (BCG) in preventing pulmonary tuberculosis (TB) underscores the need for improved TB vaccines. Recombinant BCG (rBCG) strains secreting the virulence-associated effector molecule ESAT-6 from Mycobacterium tuberculosis (Mtb) markedly improve efficacy and immunogenicity in animal models of TB but have been considered unsuitable for clinical translation due to safety concerns identified in intravenous SCID mouse models. Here, we demonstrate that pulmonary delivery fundamentally reshapes the safety and protective efficacy of the ESAT-6-secreting rBCG strains, BCG::RD1 and BCG::ESAT6-PE25SS. In sharp contrast to intravenous delivery, pulmonary administration was markedly better tolerated, improved survival, and reduced systemic dissemination and brain pathology of severely immunocompromised mice. Strikingly, pulmonary rBCG vaccination also conferred superior protection against aerosol Mtb challenge in wild-type, type 2 diabetic, and adaptive immunity-deficient Rag1-/- and Rag2-/-Il2rg-/- mice, with BCG::RD1 showing the strongest adaptive immunity-independent protection. Mechanistically, pulmonary rBCG vaccination promoted lung innate immune activation, expansion of myeloid-biased progenitors in the bone marrow, and enhanced antimycobacterial activity of macrophages, consistent with trained innate immunity. Collectively, these findings reveal that pulmonary vaccination largely overcomes safety concerns of ESAT-6-secreting rBCG strains and provide preclinical evidence for a viable strategy to improve protection against TB in immunocompromised individuals.

Dysregulated gut homing of leukocytes drives chronic inflammation in Crohns disease (CD). We employed phage display selection campaigns with libraries of stabilized, constrained peptides against endogenous conformation states of the cannabinoid receptor CB2R on human T cells, to discover novel receptor antagonists with potential to inhibit gut homing. Cluster and frequency analysis of 50,000 enriched sequences resulted in expression and functional characterisation of 10 protein candidates using assays of glucose uptake, ERK phosphorylation (pERK) and beta-arrestin recruitment. Each candidate antagonised CB2R activity with recorded IC50 values of between 5-10 nM. Cannabinoid receptor nanodisc binding experiments and SPR confirmed CB2R selectivity. SLKC_09 with an IC50 of 5.4 nM, was studied in a mouse model of chronic ileitis where it significantly inhibited gut homing of CD4+ & CD8+ naive, effector and memory cell types. Our findings highlight an alternative route to therapeutic inhibition of leukocyte trafficking in CD with a biologic inhibitor of CB2R.

The central nervous system interprets inflammatory signals in the body and directs the modulation of inflammatory responses by reflexively engaging peripheral sympathetic neurons. This includes sympathetic neurons that innervate the spleen, which can regulate immune functions and modulate inflammation. Yet, it is unclear if neuroimmune interactions involve specialised immunoregulatory sympathetic neurons, and if the immune system can reciprocally regulate peripheral sympathetic neurons to control these responses. Using retrograde tracing and single-cell transcriptomics, we find that spleen-innervating neurons are heterogeneous but do not exhibit a distinct transcriptional program indicative of specialisation for immune communication. However, we report that immune responses induced by pathogens can regulate postganglionic sympathetic neuron functions. Cytokines produced by immune cells downregulate expression of the neurotrophin nerve growth factor in spleen mesenchymal cells, leading to organ-specific sympathetic nerve retraction from the spleen. Concurrently, splenic type I interferon signalling induces inflammatory gene expression in neurons and suppresses neuron excitability. Chemogenetic activation of sympathetic neurons demonstrates an impaired anti-inflammatory capacity in the spleen during infection. These results reveal regulation of sympathetic neuronal functions by the immune system, which could support optimal generation of immune responses against pathogens.