Nature Immunology

BackgroundGastroenteric tract requires robust tolerogenic mechanisms to tolerize foreign antigens like foods and microbiota. This is critical to establish the immune homeostasis, which upon disruption, might contribute to a plethora of atopic disorders, including food allergy and eosinophilic esophagitis (EOE). Recently, there was a new subset of tolerizing dendritic cells (tolDCs), PRDM16 tolDC, discovered in the gut of mice and humans, which confers protection against food allergy. Whether an analogous population of it exist in the esophagus is unknown, especially in the context of EOE, another atopic disease associated with dietary antigens. MethodsWe thoroughly analyzed the human esophagus cell atlas single cell RNA-seq dataset and the myeloid DC-VERSE dataset, in an attempt to identify and characterize the esophageal counterpart of the intestinal PRDM16 tolDC. ResultsWe identified the esophageal counterpart of intestinal PRDM16 tolDC as a conventional type II DC subtype expressing PRDM16, termed as cDC2C (PRDM16). We demonstrated the similarities between PRDM16 tolDC and cDC2C (PRDM16) regarding their transcriptomic and functional profiles. Importantly, we found that cDC2C (PRDM16) were expanded during EOE and exhibited an anti-inflammatory phenotype, suggesting their protective role in EOE. Notably, these tolerogenic DCs were not found in other atopic diseases beyond the gastroenteric tract. ConclusionsWe here defined a novel tolerogenic DC population in human esophagus and demonstrated their implications in the pathophysiology of EOE. These findings would provide novel insights towards the tolerogenic mechanisms along the gastroenteric tract and possess translational relevance for EOE diagnosis and interventions.

Multiple sclerosis (MS) therapies primarily rely on lymphocyte depletion or trafficking blockade, carrying risks of systemic immunosuppression; however, such treatments have limited efficacy in secondary progressive multiple sclerosis (SPMS). Thus, drugs that target stage-specific inflammation without broad immunosuppression are an unmet clinical need. In this double-blind, placebo-controlled phase II trial, 30 patients with relapsing MS received weekly oral OCH or placebo for 24 weeks. In the pre-specified SPMS subgroup (n=12), OCH achieved complete relapse prevention (p=0.0003), prolonged relapse-free survival (p=0.0079), no new lesions (0/6), with no evidence of disease activity (NEDA-3) in 5/6 patients. In comparison, for the placebo-treated group, 5/6 patients suffered relapses, 2/6 patients developed new lesions, and no placebo-treated SPMS achieved NEDA-3. Invariant natural killer T (iNKT) cells, a regulatory lymphocyte population that is numerically and functionally impaired in MS, are a potential target for MS therapy. Glycolipid OCH is a selective iNKT cell stimulator, skewing the cytokine environment towards Th2. OCH treatment resulted in increased IL-4-producing Th cells in patient peripheral blood while decreasing pathogenic GM-CSF-producing Th cells. Parallel studies in mouse models of MS (EAE) corroborated this mechanism and further revealed that OCH activated gut iNKT cells. Disease amelioration by OCH depended on IL-4 and its efficacy was further enhanced by depletion of B cells. These data revealed the gut-brain axis mediation of progressive-stage pathology distinct from relapsing-remitting MS. Findings from this bidirectional translational study uncover mechanistic differences between SPMS and other types of MS and highlight divergent roles for B cells and Th cells. Furthermore, OCH exerts its therapeutic benefit via targeting mechanisms that are distinct from currently available drugs; exploiting iNKT cell regulatory potential to reprogram pathogenic T helper responses without lymphocyte depletion. The unique yet effective nature of OCH treatment positions it as an attractive future oral therapy for SPMS. One Sentence SummaryThe iNKT cell activating ligand OCH suppresses disease activity selectively in secondary progressive MS in a phase II clinical trial, revealing stage-specific IL-4-mediated immune cell interactions in MS pathology.

Epstein-Barr virus (EBV) is strongly implicated as an essential environmental trigger of multiple sclerosis (MS), yet the host genetic mechanisms governing EBV activity and how infection triggers the disease are not known. We developed a pipeline to quantify EBV DNA from whole-genome sequencing data and applied it to population-scale cohorts. Using this pipeline, we performed a cross-ancestry genome-wide association study (GWAS) of EBV DNA positivity in 617,186 individuals and identified 39 independent susceptibility risk loci, with the strongest associations in the HLA region. We validated this finding in our independent cohort (N=94) and found that quantitative PCR (qPCR)-confirmed EBV DNA positive individuals were enriched in the top decile of EBV polygenic risk scores (PRS) containing newly discovered loci. A significant overlap with genetic variants associated with MS risk was observed. PRS and Mendelian randomization analyses further supported a causal role of EBV activity on MS risk, which was also seen in other autoimmune diseases. A meta-analysis of qPCR based case-control studies showed elevated EBV DNA positivity in MS. By establishing a single-cell RNA-seq method optimized for EBV detection, we identified EBV-infected B cells, primarily in memory B cells, atypical B cells and antibody-secreting cells from MS and healthy individuals. Notably, EBV-infected memory B cells and atypical B cells showed strong upregulation of cytokines and costimulatory signals that influence T cell activation, IFNg secreting Tregs, and regulators of B cell differentiation and survival. EBV-infected memory B cells also upregulated risk genes from both the EBV and MS GWAS, suggesting that EBV-infected B cells constitute a critical hub that modulates T cell responses while simultaneously activating MS susceptibility pathways within the B cell compartment. Together, these findings define a genetic and cellular framework linking EBV infection to the initiation of MS.

Antiphospholipid syndrome (APS) and systemic sclerosis (SSc) are immune-mediated multisystem autoimmune diseases with distinct clinical phenotypes but overlapping pathogenic themes, including immune dysregulation, chronic inflammation, and endothelial injury. Using peripheral blood transcriptome datasets from the Gene Expression Omnibus (GSE102215: 9 APS/9 controls; GSE231691: 49 SSc/18 controls), we performed differential expression analysis within each cohort (limma; |log2FC|>1, P<0.05) and identified 281 genes dysregulated in the same direction in both diseases (100 upregulated and 181 downregulated). Enrichment analyses highlighted interferon-related and cytokine/inflammatory signaling programs in APS and SSc. To derive a compact diagnostic signature, we combined random forest feature ranking with a single-hidden-layer artificial neural network, prioritizing five shared candidate biomarkers (S100A8, IER5L-AS1, LTK, PRR5-ARHGAP8, and PCDH1). Each gene showed consistent case-control differences in both cohorts (P<0.001) and achieved good discrimination (AUC>0.75), with S100A8 performing most consistently (AUC=0.98 in APS; AUC=0.88 in SSc). CIBERSORT deconvolution indicated a myeloid-skewed blood profile in both diseases, characterized by higher neutrophil and monocyte/macrophage signals; SSc additionally showed stronger inferred CD4+ T cell and NK cell signals. S100A8 expression correlated with inferred neutrophil abundance in both cohorts (APS r=0.62; SSc r=0.58; P<0.05). Finally, miRNA-target prediction and DSigDB drug-signature enrichment generated regulatory and pharmacologic hypotheses, including immune-regulatory miRNAs (e.g., miR-155 and miR-146a) and candidate compounds (celecoxib, tamibarotene, HMN-176, and XMD14-99). Overall, these results nominate shared blood transcriptional markers and immune correlates across APS and SSc for follow-up validation.

RIG-I is a cytosolic immune receptor that provides the first line of defense by detecting viral RNA and triggering antiviral responses. Its physiological role in humans remains unclear, as no patients with complete RIG-I deficiency have yet been reported. We identified a critically ill COVID-19 patient with severe RIG-I deficiency caused by heterozygous RIG-I G731R, a novel dominant loss-of-function variant. The G731R mutation in helicase motif VI disrupts the arginine finger, impairing the ATPase activity of RIG-I, but not its RNA-binding ability. However, viral RNA binding fails to expose the signaling domains, thereby impairing the IFN-{beta} response of G731R. Instead, G731R competes with wild-type RIG-I, exerting a dominant negative effect. The loss-of-function is caused by bulky-charged substitutions at G731, as alanine or leucine substitution results in an unexpected gain-of-function phenotype. These findings highlight the importance of uncompromised RIG-I function for human antiviral immunity and the pleiotropic effects of single mutations.

Sjogrens disease (SjD) is a chronic autoimmune disorder characterized by inflammation of the exocrine glands, leading to dry mouth and dry eyes. This study investigates the role of interleukin-9 (IL-9) and T helper 9 (Th9) cells in the pathogenesis of SjD. We found that serum IL-9 levels were significantly elevated in SjD patients and correlated with clinical laboratory parameters, including autoantibody production. In a mouse model of SjD, IL-9 and Th9-associated cytokines were also elevated, and Th9 cells were enriched in the salivary glands. Our results suggest that IL-9 is produced by multiple cell types, including macrophages, CD4+ T cells, and NK cells, and that Th9 cells contribute to the development of SjD by promoting inflammation and autoantibody production. We also found that Th9 and Th17 polarization conditions increased Th2 and Th17 cells in SjD mice, indicating a shared epigenetic program that renders T cells permissive to multiple differentiation pathways. Anti-IL-9 treatment had a sex-dependent effect, reducing autoantibody production in male mice but worsening focal glandular infiltration in female mice. Our findings suggest that IL-9 plays a complex role in SjD pathobiology, contributing to both local immunoregulation and systemic autoantibody response. Overall, this study offers new insights into the role of IL-9 and Th9 cells in SjD, highlighting the potential for therapeutic targeting of the IL-9/Th9 axis in the treatment of this disease.

The Endoplasmic Reticulum AminoPeptidase 2 (ERAP2) gene encodes an aminopeptidase involved in antigenic peptide processing for the MHC-I pathway. Genetic variants in the ERAP2 gene are associated with autoimmune conditions and infectious diseases. The linkage between genetic variants in the ERAP2 gene has given rise to the prevailing assumption that a single ERAP2 allotype with invariant amino acid sequence accounts for all immunological functions of ERAP2. Here, we show by analyzing exon-sequencing data from 160,000 individuals that 15 missense amino acid variants across the ERAP2 gene result in an array of different protein allotypes that are maintained in the European population. These allotypes can be divided into three haplotype groups, defined by the genotypes of two common splice-altering variants. We found novel associations between newly identified protein allotypes and immune-mediated diseases, suggesting that ERAP2 functional variation modifies disease susceptibility at the population level. An MHC class I antigen presentation assay revealed that disease-associated ERAP2 allotypes differ in their capacity to generate antigenic peptides for MHC-I presentation, resulting in differential activation of an antigen-specific T-cell receptor compared to non-disease-associated allotypes. These findings provide strong evidence that ERAP2 function is allotype-dependent and demonstrate that ERAP2 diversity shapes MHC-I antigen presentation and T-cell immunity. Significance statementThe ERAP2 enzyme modulates adaptive immunity and plays a role in autoimmunity, infection, and cancer. The authors discovered that a variety of protein allotypes of ERAP2 are maintained in the human population. Allotypes that increase disease risk for autoimmune and cardiovascular conditions are functionally distinct in their capacity to activate T-cells. The results of this study demonstrate that ERAP2 is a functionally diverse immune modulator that contributes to immune variation and influences susceptibility to immune-mediated diseases.

AimsGestational diabetes mellitus (GDM) is the most common pregnancy-related medical complication. GDM is linked to aberrant immune responses in both mothers and offsprings, specifically, the subsequent development of inflammatory diseases. Whereas prior research has focused on specific immune cell subsets, a comprehensive overview of the impacts of GDM on maternal and fetal immune landscape is lacking. Here, we aim to comprehensively decipher how GDM modulates various immune cell populations in mothers and offsprings. MethodsA prospective, longitudinal case-control study was carried out. Maternal blood from GDM-affected (GDM, n=18) and non-GDM-affected (Ctrl, n=21) mothers were collected at ante-(36-38 weeks of gestation) and post-partum (6-8 weeks post-partum) timepoints. Cord blood from GDM (n=7) and Ctrl (n=11) pregnancies were collected upon C-section. They were analyzed with the state-of-the-art cytometry by time of flight (CyTOF) with a 40-marker panel. Additionally, a publicly available RNA-seq dataset for cord blood mononuclear cells was re-analyzed to confirm results from CyTOF experiments. ResultsCompared to Ctrl, GDM was associated with more activated maternal T cell subsets ante-partum, including increased CD45RO+ and Ki67+ CD4+ T cell populations, which reverted post-partum. GDM-affected maternal innate lymphoid cell (ILC) also exhibited increased granzyme B production ante-partum. On the other hand, in GDM-impacted cord blood, fetal T and B cells were more activated, displaying less naive and more effector phenotypes, further supported by RNA-seq analyses. ConclusionsOur comprehensive analyses revealed that GDM is linked to profound changes in the immune landscapes of the mothers (ante-/post-partum) and foetuses (at birth), casting novel insights towards GDM pathophysiology. Longitudinal immune profiling might be warranted for early detection and stratification of risk, and development of targeted interventions to prevent inflammatory disorders in GDM mothers and their offspring. Research in contextO_LIWhat is already known about this subject? O_LIThe maternal and intrauterine environments are important contributors to long-term health outcomes of mothers and offsprings. C_LIO_LISome maternal and fetal immunity changes have been observed in gestational diabetes mellitus (GDM)-affected pregnancies. C_LIO_LIGDM is associated with increased risk of later-life metabolic and inflammatory diseases in mothers as well as offsprings. C_LI C_LIO_LIWhat is the key question? O_LIWhat are the longitudinal alterations in maternal and fetal immune landscapes in GDM-affected pregnancies? C_LI C_LIO_LIWhat are the new findings? O_LIHigh-dimensional immune profiling provided the most comprehensive overview of alterations in maternal and fetal immune landscapes associated with GDM. C_LIO_LIGDM is associated with skewing of maternal CD4+ T cell and ILC towards activated phenotypes ante-partum. C_LIO_LIGDM is linked to more activated fetal T and B cell profiles. C_LI C_LIO_LIHow might this impact on clinical practice in the foreseeable future? O_LIUnderstanding the complex alterations in the maternal and fetal immune landscape in GDM-affected pregnancy provides insights into the long-term impacts of GDM on the mother and offspring. C_LI C_LI

Vaccination frequently elicits suboptimal immunogenicity in organ transplant recipients, particularly those on long-term immunosuppressive therapy, highlighting the need for improved understanding of immunosuppression mechanisms and optimized vaccination strategies. This study enrolled a cohort of 132 individuals and observed significantly lower antibody levels in kidney transplant recipients (KTRs) compared to non-transplant controls (non-KTRs). Antibody levels were inversely associated with both the dosage and duration of immunosuppressive therapy. Complementary small animal studies demonstrated that immunosuppressive treatment dosage-dependently and reversibly impaired antibody production, primarily by depleting immune cells, notably B cells. A single shot of adenoviral vector-based vaccines demonstrated enhanced immunogenicity relative to two shots of alum-adjuvanted protein vaccines, inducing potent neutralizing antibodies (NAbs) and a Th1-biased T-cell response even under continuous immunosuppression. The enhanced response was driven by reduced interference from pre-existing antibodies, sustained transgene expression, and the reprogramming of lipid metabolism to activate T and B cells. Our findings advocate for tailored vaccination strategies, positioning adenoviral vectors as a candidate modality for this vulnerable population.

BackgroundInfluenza vaccination and bacterial colonization both shape immunity in the respiratory tract, yet their combined impact on the human lung mucosa remains poorly understood. Secondary bacterial pneumonia following influenza infection is a leading cause of mortality, underscoring the need to define how vaccines and microbes intersect at the airway interface. MethodsUsing the Experimental Human Pneumococcal Challenge (EHPC) model, we examined how intramuscular inactivated (TIV) and nasal live attenuated (LAIV) influenza vaccines, with or without Streptococcus pneumoniae colonization, modulate lower airway immunity. Bronchoalveolar lavage samples from 22 adults were profiled by single-cell RNA-seq (>40,000 cells), flow cytometry, cytokine multiplexing, and macrophage functional assays. FindingsLAIV recipients who became colonized with S. pneumoniae displayed heightened influenza-specific CD4{square} T cell responses and enhanced alveolar macrophage (AM) opsonophagocytic activity, showing that nasal bacterial colonization can act as natural mucosal adjuvant. Single-cell transcriptomics revealed four AM gene modules; among them, an interferon-driven "anti-microbial" program correlated with enhanced phagocytosis, whereas a complement- and antigen-presentation module associated with IFN{gamma}-iNOS/ROS signaling was attenuated in colonized vaccinees. Given that AMs are poor antigen-presenting cells, this shift likely reflects reprogramming toward cytokine-mediated immune modulation rather than direct T cell activation. The elevated influenza-specific CD4{square} T cell responses may instead represent feedback from enhanced local activation. Together, these data indicate that vaccination and colonization synergize to rewire AM-T cell communication, fine-tuning antiviral and antibacterial defenses. Similar transcriptional perturbations in public COVID-19 and lung cancer datasets underscore the broader relevance of these macrophage modules across lung disease contexts. ConclusionsOur findings define how influenza vaccination and pneumococcal colonization converge in the human lung to reprogram AM-T cell crosstalk, enhancing local immune responses and protective immunity. By uncovering conserved macrophage modules and mechanisms that shape mucosal defense, this study provides a framework for designing next-generation respiratory vaccines and strategies to mitigate post-viral bacterial pneumonia.

Why do some individuals develop mild COVID-19 while others progress to severe disease remains a central challenge in SARS-CoV-2 immunology. In this study, we leveraged the BACO Cohort - a unique historical cohort of immunologically naive, hospitalized COVID-19 patients from the first pandemic wave - to investigate early immune determinants of clinical disease trajectories. Integrating bulk RNA-seq, Olink proteomics, and systems serology, we identified two fundamentally distinct immune trajectories according to disease phenotypes. Severe patients exhibited upregulation of proinflammatory genes and monocyte-associated transcripts, alongside downregulation of genes related to T cell responses and immune signaling. Notably, an upregulation of inhibitory Fc-receptor-associated gene was also found in severe cases. In contrast, mild cases showed coordinated lymphoid activation and limited inflammation. Building on these findings, we performed a functional profiling of Fc-effector activity in the polyclonal serum of the patients and found that monocyte-mediated phagocytosis was a common feature of mild disease. Interestingly, this response was mainly driven by rapid induction of S1-specific antibodies. Conversely, severe patients tended to generate higher levels of S2-biased antibodies early after infection with poor Fc-effector functionality. Together, these findings demonstrate that early S1-directed, Fc-competent humoral immunity is a key determinant of favorable COVID-19 outcomes, while delayed functional maturation and early S2 bias characterized severe disease in the BACO cohort.

Immune checkpoint inhibitors (ICIs) have transformed cancer treatment but commonly cause immune-related adverse events (irAEs), whether administered as monotherapy or in combination with other oncological agents. We present the first reported case of ICI-induced granulomatous sialadenitis in a male patient in his mid-fifties with BRAF-V600E-mutated papillary thyroid carcinoma who received sequential treatment with BRAF/MEK inhibitors followed by pembrolizumab. The patient experienced acute-onset severe xerostomia and salivary hypofunction, prompting ICI cessation and salivary gland biopsy. Integrative analysis using histology, single-cell RNA sequencing, and spatial transcriptomics revealed macrophage- and T-cell-mediated epithelial damage driven by epithelial senescence and Th1-polarized inflammation. Corticosteroid therapy reduced granuloma burden and improved salivary flow rates and tissue architecture; however, extensive fibrosis persisted despite treatment. These findings underscore the critical importance of early irAE recognition and intervention to preserve glandular function and enable continuation of cancer therapy.

BackgroundAn adverse female sex-bias exists across many autoimmune disorders, yet its underlying mechanisms, particularly the role of sex hormones, remains poorly understood. Furthermore, the physiological influence of sex hormones in regulating T cell function remains undefined. We examined for the critical role of estrogen and progesterone, in regulating CD4+ T cell responses, specifically with respect to inflammation and their bone erosion potential in RA. MethodsInflammatory markers, circulating antibodies, sex hormone receptors, ER and PR levels were investigated in both RA patients and controls. Further, RA CD4+ T cells were stimulated in varying concentrations of estradiol and progesterone and assessed for modulation in cytokines, transcription factors, RANKL, and FasL expression. Subsequent ex-vivo studies were performed to examine the role of sex hormones in modulating T cell responses. ResultsRA patients displayed systemic inflammation and high circulating antibodies, with significantly higher expression in synovial fluid. Higher expression of ER and PR was evinced on RA CD4+ T cells. Upon hormone stimulation, two cohorts of patients namely responders and non-responders were observed with respect to modulation in cytokines, transcription factors, RANKL, and FasL expression. Our ex-vivo Th1 and Th17 cells demonstrated that sex hormones play a physiological role in modulating inflammation and have bone erosion potential. ConclusionOur findings demonstrate the pivotal significance of sex hormones in modulating TCR responses, thereby regulating inflammation and bone erosion in RA pathology. Further dissection of TCR signaling pathways with respect to sex hormone stimulation may provide promising targets for therapeutic implications. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/25342530v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@b74525org.highwire.dtl.DTLVardef@1cc01aorg.highwire.dtl.DTLVardef@1881e4forg.highwire.dtl.DTLVardef@17de2a8_HPS_FORMAT_FIGEXP M_FIG C_FIG

In this study, we provide a comprehensive characterization of the alveolar immune landscape in patients suffering from severe acute respiratory failure, predominantly caused by pneumonia or acute respiratory distress syndrome, conditions defined by intense pulmonary inflammation and immune dysregulation. Despite diverse underlying causes, the overall composition of alveolar immune cells was largely consistent, with neutrophils and macrophages comprising the majority of cells. However, the maturation and activation states of immune cell subsets varied significantly, not only between patients with and without pneumonia, but also among pneumonia cases stratified by pathogen type. We also observed dynamic shifts in immune cell subsets over the disease course and found that an increased proportion of CD123bright immature neutrophils and a reduction in alveolar resident macrophages were associated with increased 28-day mortality. Integration with alveolar cytokine profiles revealed strong correlations between immune cell populations and the local cytokine milieu. These findings highlight the importance of assessing immune cell function, not merely abundance, through broad and longitudinal investigation to better understand the pathophysiology of acute respiratory failure and to guide precision immunomodulatory therapy.

Newly emerging influenza virus strains pose a constant threat as they encounter a population lacking neutralizing antibodies against the new strain. However, cross-reactive non-neutralizing antibodies (nnABs) may be present and assist in mitigating disease symptoms via various effector mechanisms, including antibody-dependent cellular cytotoxicity (ADCC). Although nnABs to influenza virus have received more attention lately, little information is available on their age-related prevalence, steady-state levels, functional properties, and changes in these parameters over time. Using longitudinal samples from adolescents, adults, and older adults, collected before and after the 2009 swine flu pandemic, we comprehensively characterized the specificity and functionality of nnAB responses against H1N1 pandemic 2009 (H1N1pdm09) virus. Remarkably, all participants exhibited cross-reactive antibodies to this virus before having encountered it through infection or vaccination, with the highest baseline levels observed in older adults. The levels of these IgG antibodies showed a strong correlation with engagement of fragment crystallizable {gamma} receptor IIIa (Fc{gamma}RIIIa) and ADCC activity, both of which were notably lower in adolescents compared to adults and older adults. Without infection or vaccination, average amounts of H1N1pdm09-reactive antibodies remained relatively stable on population level over the 5-year study period. However, on an individual level, substantial increases and decreases occurred. H1N1pdm09 infection or vaccination significantly enhanced specific antibody levels and the Fc{gamma}RIIIa-engaging capacity of these antibodies in all age groups. ADCC-mediating antibodies increased however only in adolescents, reaching the same level as observed in the adult groups. Taken together, our results demonstrate the presence of cross-reactive, non-neutralizing, functional, and boostable antibodies against a never-encountered influenza virus strain across all age groups. These antibodies can potentially contribute to protection from severe disease. Accordingly, in case of a newly emerging virus, their further enhancement by vaccination could be beneficial as an immediate protective measure before a strain-specific vaccine becomes available. Author summaryNearly everyone has contracted influenza and/or has been vaccinated against influenza several times over the years. While the antibodies raised during these earlier encounters will not prevent infection by a newly emerging influenza virus strain, they can help to protect from severe disease. Therefore, it is important to determine the prevalence and quantity of these antibodies, understand their mechanisms of action, assess their persistence over time, and examine potential age-related differences in these parameters. We studied antibody responses to the H1N1pdm09 virus in blood samples of young, adult, and older adult individuals from a large cohort study. Irrespective of age, all blood samples contained antibodies that reacted with a never-before-encountered influenza virus strain. The amounts of these antibodies were initially lower in adolescents but with time increased, reaching the same levels as observed in adults. Importantly, infection with or vaccination against the new virus strengthened the responses in all age groups. We conclude that boosting such broadly-reactive antibodies through vaccination could serve as an immediate strategy when a new virus emerges, buying critical time to develop a more specific vaccine.

BackgroundAtopic dermatitis (AD) is a chronic skin disease that typically occurs in early childhood. In this cross-sectional case-control study, our objective was to employ machine learning approaches to identify novel clusters of protective or susceptibility features associated with AD. Methods and FindingsWe utilised an integrated dataset comprising previously established environmental, cytokine, antibody, and gene expression data from AmaXhosa children, both healthy and with AD, living in either rural or urban settings of South Africa, aged 12-36 months. The applied machine learning methods included the GeneSelectR workflow to identify a subset of relevant genes, the calculation of SHAP values to explain the machine learning output, and the use of DIABLO to integrate the datasets for a comprehensive analysis. Key findings included the identification of a protective cluster of environmental features primarily found in the rural setting, which were correlated with plasma cytokine levels and with expression of autophagy-related genes. Additionally, we identified AD susceptibility clusters where levels of allergen-specific and total IgE antibodies correlated with the cytokines MCP-4 and TARC. Lastly, we identified an RNA-Seq feature signature specific to the disease endotype. ConclusionsThe application of various machine learning methods enabled the identification of significant factors associated with AD in a complex, multi-modular dataset, making the output explainable and potentially informing targeted interventions and improved diagnostic criteria.

Coccidioidomycosis presents clinically as a spectrum ranging from self-limiting Uncomplicated Valley Fever (UVF) in most cases to life-threatening Disseminated Coccidioidomycosis (DCM) in rare individuals. A few patterns of immunologic deficits allowing for dissemination have been identified, though the specific defects in most individuals with DCM remain undefined. We hypothesized that chronic antigen exposure in DCM engenders a state of T cell exhaustion. From a cohort of over 300 subjects with confirmed diagnoses of coccidioidomycosis, circulating T cell phenotypes were characterized via flow cytometry and Coccidioides-specific T cell responses were measured using the Activation-Induced Marker (AIM) assay. Male sex was significantly associated with disseminated disease (odds ratio 2.5; 95% CI: 1.5 - 4.0). 52% of subjects showed Coccidioides-specific T cell responses in our AIM assay. We noted a significant difference in subjects sampled in the first year of diagnosis, where only 8% of DCM subjects had T cell responses during this time, as compared to 44% of UVF subjects (p = 0.04). Among DCM patients with detectable AIM responses, CD4+ T cells demonstrated an exhausted phenotype with elevated PD-1 expression compared to UVF subjects. In vitro PD-1 blockade augmented IFN{gamma} production in most tested DCM subjects. These findings suggest that dissemination may occur in some individuals during a period of impaired antigen-specific T-cell activity. Importantly, these responses can be augmented in vitro by PD-1 blocking antibodies, supporting further study of immune checkpoint therapy as an adjunct to antifungal treatment in disseminated coccidioidomycosis.

BackgroundTuberculosis (TB) and HIV co-infection cause profound immune dysregulation. Understanding how these infections alter immune cell distribution across systemic and tissue compartments is critical for improving therapeutic and vaccine strategies. MethodsFlow cytometry was used to quantify CD4 and CD8 T cells, B cells, and tissue-resident memory (TRM) T and B cells in peripheral blood mononuclear cells (PBMCs), lung tissue, bronchoalveolar lavage (BAL), spleen, and lung-draining hilar lymph nodes (HLN) from individuals with pulmonary TB (PTB), disseminated TB (Diss TB), HIV only, or both TB and HIV infections. ResultsCD4 T cell frequencies were significantly reduced in multiple compartments of HIV infected subjects, irrespective of TB status, indicating systemic immune suppression. CD8 T-cell frequencies were elevated in the blood of HIV-infected individuals, suggesting a compensatory response to CD4 T-cell loss. B-cell frequencies were reduced in PBMCs and lung tissue of TB subjects, regardless of HIV status. Notably, CD4 TRM T cells were specifically depleted in lung tissue of HIV/TB co-infected individuals, whereas TRM B cells were selectively depleted in TB subjects, independent of HIV infection. ConclusionTB and HIV drive distinct and compartment-specific TRM cell loss in infected tissues. HIV primarily targets CD4 TRM T cells, while TB specifically depletes TRM B cells, highlighting separate mechanisms of tissue-resident immune disruption. These findings emphasize the importance of tissue-specific immune analyses and provide new insights for targeted vaccine and immunotherapy strategies.

Immune imprinting, also known as immune history, is a core aspect of adaptive immunity that influences antibody responses to future antigen exposures. Nevertheless, the impact of sequential flavivirus vaccinations on epitope targeting and antibody activity in humans remains incompletely understood. This question is particularly important in regions where the inactivated Japanese encephalitis virus (JEV) vaccines and the live-attenuated dengue virus (DENV) vaccines are used, as both have been associated with an increased risk of symptomatic dengue infection and severe illness. We studied the impact of prior inactivated JEV IXIARO vaccination and simultaneous vaccination on humoral immunity following live-attenuated dengue CYD-TDV vaccination. Long-term analysis showed that JEV IXIARO priming guides the dengue vaccine-induced antibody response toward conserved fusion loop epitopes (FLEs) of the DENV envelope protein, as indicated by 4G2 FLE-bias. This imprinting was characterized by higher levels of 4G2 FLE-like antibodies, rapid recall responses after dengue vaccination, and broad but low-potency neutralization across dengue serotypes and Zika virus. Notably, 4G2 FLE-focused responses correlated with higher Fc{gamma}RIIa-mediated antibody-dependent enhancement relative to neutralization potency, suggesting functional effects beyond neutralization. To better understand epitope dominance within the native envelope, we used a structurally defined fusion loop epitope mutant (FLE-mut) envelope dimer assay. Disrupting fusion loop accessibility significantly decreased antibody binding, confirming that FLE-specific antibodies are a major component of the response after sequential vaccination. Importantly, a complete series of live-attenuated dengue vaccine reduced 4G2 FLE bias, encouraged the recruitment of non-fusion-loop epitopes, and lessened Fc{gamma}RIIa-biased antibody activity. Overall, these results show that vaccination platform, timing, and regimen are critical determinants of epitope dominance and antibody quality following flavivirus vaccination.

ObjectivesTo identify and validate plasma host-response protein biomarkers that improve discrimination of bacterial infection in febrile infants [&le;]90 days of age, and to assess whether novel biomarkers add value beyond established markers. MethodsSub-study of the prospective multicentre Febrile Infant Diagnostic Assessment and Outcome (FIDO) cohort. Novel biomarkers were identified through plasma proteomic profiling (Olink(R)) and combined with biomarkers and signatures from the literature for verification using Luminex and ELISA platforms. Diagnostic performance of novel biomarkers, established markers (CRP, PCT), and multi-protein signatures was evaluated. ResultsProteomic profiling of 110 samples identified 174 proteins differentially expressed between bacterial and viral infections, revealing distinct pathogen-specific immune signatures. Verification in the full cohort (n=445) demonstrated PCT had the highest individual accuracy for invasive bacterial infection (IBI) (AUC 0.89). Combining PCT with novel biomarkers, particularly lipocalin-2 (LCN2), improved discrimination (AUC 0.96). Diagnostic performance for the combined IBI/urinary tract infection (UTI) outcome was consistently lower (AUC <0.8). ConclusionsFebrile infants demonstrate biologically coherent host-response signatures that can be leveraged diagnostically. A PCT-LCN2 combination showed excellent accuracy for identifying IBI and may support future biomarker-guided diagnostic strategies, while reliable discrimination of UTI remains challenging.