Immunology & Cell Biology

Background and Aims: Alterations in immunoglobulin G (IgG) N-glycosylation are implicated in inflammatory bowel disease (IBD); however, the robustness of IgG glycan signatures across IBD cohorts with diverse demographics and geographic origins remains underexplored. We aimed to determine whether compositional data analysis (CoDA) and machine learning (ML) can identify IBD-related IgG N-glycan signatures and whether these signatures capture disease-associated acceleration of biological aging. Methods: We analyzed the IgG glycome profiles of 1,367 plasma samples collected from healthy controls (HC), symptomatic controls (SC), and people with newly diagnosed Crohn's (CD), and ulcerative colitis (UC) across four cohorts (UK, Italy, United States, and Netherlands). IgG glycosylation was analyzed by ultra-high-performance liquid chromatography, yielding 24 total-area-normalized glycan peaks (GPs). Analyses were performed using cross-sectional data obtained at baseline. CoDA-powered association analyses were used to identify disease-related effects on GPs while controlling for demographic covariates. ML models were trained and evaluated to assess generalizability to unseen cohorts and demographic subgroups, with a focus on discrimination and reliability. Results: Across all cohorts, people with IBD demonstrated accelerated biological aging as quantified by the GlycanAge index. This was accompanied by consistent reductions in IgG galactosylation, with effects partially modulated by age. Classification models trained on glycomics and demographics achieved robust discrimination (AUROC~0.80) between non-IBD (HC+SC) and IBD across cohorts. Conclusion: These findings reveal accelerated biological aging in people with IBD and support the translational potential of IgG glycans as biomarkers and a novel route toward clinically interpretable personalized risk estimates.

Unbiased classification of equine dendritic cells (DC) is necessary to address various research questions such as the role of DC subsets in immune-mediated diseases of horses. We applied single-cell RNA sequencing (scRNA-seq) on DC enriched from the blood of two horses. All main DC subsets were detected by key gene expression, including conventional DC type 1 (cDC1; XCR1) and type 2 (cDC2; FCER1A, CD1E) as well as plasmacytoid DC (pDC; TCF4). In addition, we detected a small cluster of hematopoietic progenitors, as well as transitional DC (tDC; FCER1A, TCF4) and putative DC type 3 (DC3; FLT3, CD163). Our data confirms the previously reported phenotype of equine pDC (Flt3+MHC-IIlowCADM1lowCD172aint), cDC1 (Flt3+MHC-IIhighCADM1highCD172alow-int) and cDC2 (Flt3+MHC-IIhighCADM1intCD172ahigh), while also highlighting considerable CD14 expression for cDC2. Two subclusters of equine cDC2 were found to be enriched in FCER1A or CX3CR1 transcripts (cDC2.1 and cDC2.2, respectively), with suggested enhanced extravasation and T-cell stimulatory capacities of the latter. Conservation of DC subsets across species (horse, pig, human, mouse) was illustrated by enrichment analyses with subset-specific gene signatures and by cross-species data integration with publicly available scRNA-seq datasets. Our atlas of equine blood DC is a valuable resource for comparative analyses, and it forms the foundation for understanding the involvement of distinct DC subsets in infections and immune-mediated pathologies.

Inflammation is a key driver of hematopoietic dysfunction in myeloid malignancies, but its role in the context of hypomethylating therapy remains incompletely understood. Although 5-Azacytidine is used posttransplant in high-risk myelodysplastic syndrome (MDS), only 50% of patients show a clinical response. We provide evidence that inherent inflammatory properties of healthy donor CD34+ stem cells exist that are likely to contribute to the "response" seen in MDS patients. These are linked to epigenetic priming of the myeloid niche, resulting in S100A8/A9-driven inflammatory program that promotes functionality of immature NK cells. Using in vitro differentiation systems, multi-omic profiling, and a S100A9-/- mouse model, we find that 5-AzaC modulates inflammatory transcriptional programs through epigenetic rewiring of upstream regulatory elements. Loss of S100A9 disrupts myeloid differentiation, impairs NK cell maturation, and alters key developmental regulators including CEBPB, JUN, and NFIL3. In vivo, 5-AzaC restores these defects and primes NK cells in a time- and context-dependent manner. Re-analysis of the published Australian MDS/CMML cohort shows that "responders" display increased S100A8/A9 expression together with enhanced IFN-{gamma}, IL6-JAK-STAT3, and TNF signaling. These findings suggest that inflammatory myeloid programs may serve as predictive biomarkers and therapeutic targets to enhance NK cell-mediated graft-versus-leukemia activity posttransplant. SummaryO_LIWe provide compelling evidence that inherent properties of healthy donor CD34+ hematopoietic stem cells (SCs) exist that are likely to contribute to the "response" seen upon pre-emptive posttransplant 5-AzaC therapy of patients with high-risk myelodysplastic syndrome (MDS). C_LIO_LIThese properties are linked to a distinct form of epigenetic plasticity at upstream-located transcription factor (TF) binding sites. This may indirectly contribute to acute S100A8/A9-driven inflammation, which is demonstrable in distinct monocyte subsets and, importantly, also in NK cells thereby determining the characteristics of inflammatory monocyte-NK cell crosstalk. C_LIO_LIMice with a targeted deletion of S100A9 fail to upregulate CEBPB / JUN and NFIL3 which results in impaired myeloid priming and dysfunctional NK cell maturation, respectively. C_LIO_LIRe-analysis of the Australian MDS/CMML cohort confirms that MDS patients that "respond" to 5-AzaC exhibit activated IFN-{gamma}, IL6-JAK-STAT3, and TNF-signaling pathways in the context of upregulated S100A8/A9 after six months of treatment. C_LIO_LIOur study indicates that screening of healthy donors SCs for specific inflammatory markers in early developing monocytes could be used as a marker to predict which donor will have the potential of generating a S100A8/A9-driven inflammatory response. This may help identify patients with MDS as well as AML who are likely to benefit from low-dose, short-term 5-AzaC therapy as early as day 7 after transplantation, potentially resulting in increased graft-versus-leukemia (GvL) activity. C_LI

The human neonatal immune system is developmentally specialized to balance the unique requirements of perinatal transition. Disruption of this finely tuned balance, as in preterm birth, may have profound consequences for immunity and overall health. However, the impact of prematurity on immune composition and functional responsiveness across gestational ages (GA) remains incompletely understood. Single-cell profiling has advanced our understanding of neonatal immunity, yet most studies were limited to unimodal readouts, narrow GA windows, or baseline function. Here, we present a comprehensive human neonatal CITE-seq atlas (82 samples from 25 neonates and 10 adults as controls) at the first days of life covering a wide GA range and integrating baseline and stimulated conditions. Most notably, we identify a GA-dependent immune transition point centered around 32 weeks of GA, which discriminates extremely and very preterm neonates (GA <32wks) from those of higher GA ([&ge;]32wks). In particular, early-life immunity in extremely and very preterm infants showed CD15+ granulocytic myeloid derived suppressor cell-like predominance, whereas more mature neonates exhibited interferon-primed transcriptional profiles. This resulted in divergent myeloid-to-lymphocyte signaling networks and qualitatively distinct NK- and T-cell bystander responses upon activation. Together, these findings show that intrauterine development imprints GA-specific immune programs. By defining a developmental transition around a GA of 32 weeks that regulates baseline and induced responses of neonatal immune cells, our atlas provides a framework for understanding the vulnerability of preterm infants and thus may pave the way for developing GA-adapted immunomodulatory strategies. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC="FIGDIR/small/715643v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@1db4534org.highwire.dtl.DTLVardef@9c9665org.highwire.dtl.DTLVardef@55f063org.highwire.dtl.DTLVardef@190a52_HPS_FORMAT_FIGEXP M_FIG C_FIG

T cell development in the thymus is a tightly regulated process where epigenetic modifications, such as histone 3 lysine 27 acetylation (H3K27ac), play a crucial role in controlling the activation of genes. The epigenetic regulation of human mucosal-associated invariant T (MAIT) cell development is unknown; we mapped the regulatory chromatin landscape in the three developmental stages of thymic MAIT cells to identify the regulatory elements and enhancer activity involved in thymic maturation and analysed whether these chromatin dynamics are associated with the acquisition of effector programs in developing MAIT cells. Utilising cleavage under target and tagmentation (CUT&Tag), genome-wide H3K27ac profiles were generated and combined with transcriptome data from thymic MAIT cells, which revealed how developmental shifts in enhancer activity correspond to changes in gene expression. In total, 41,958 genomic regions with H3K27ac signal were identified in MAIT cells across the three development stages, of which 1,200 regions showed acetylation changes during differentiation from stage 1 to stage 3. At dynamic regions, the greatest differences were observed between stage 1 and stage 3, highlighting a progressive gain or loss of H3K27ac during MAIT cell development. Overall, MAIT cell maturation was associated with the gradual accumulation of H3K27ac at promoters and enhancers, which closely correlated with gene expression changes during development. Stage-specific enrichment of H3K27ac was observed at key transcription factor gene loci involved in MAIT cell development, including ZBTB16 (PLZF), EOMES, RUNX3, NFATC2, FOXO1, TGIF1, IRF1, and MAF genes. Epigenetic remodelling was also observed at cytokine and cytokine receptors (IL7R, IL18R1, IL23R, IFNG), chemokines and chemokine receptors (CCL4, CCL5, CCR5, CCR9, CXCR4, CXCR6), as well as several surface molecules with known immunological function. Our work reveals a previously uncharacterised epigenetic profile of human MAIT cells that regulates and inuences their development.

Peptidase inhibitor 16 (Pi16)-expressing fibroblasts are found across tissues and species, but their functional role is unclear. As fibroblasts and macrophages have been proposed to exist in a reciprocal circuit, we hypothesized Pi16+ fibroblasts may regulate macrophage homeostasis. Flow cytometry revealed [~]80% of skin fibroblasts express Pi16, leading us to investigate the role of these cells in maintaining a macrophage niche in this tissue. We generated an in vivo system where fibroblast-derived Colony Stimulating Factor 1 (Csf1) was constitutively eliminated in Pi16+ fibroblasts by crossing animals with a Csf1fl/fl allele to mice in which the gene Pi16 drives an IresCre cassette. Deletion of Csf1 in Pi16+ fibroblasts resulted in significant diminishment of CD64+ and CD11c+ macrophages alongside expansion of PDPN+YFP+ fibroblasts. Alterations in cell population dynamics coincided with thickening of both the dermis and fascial compartments of the skin. Deletion of Csf1 in Pi16+ fibroblasts delayed early wound healing in a unsplinted mouse model. Loss of PI16+ fibroblasts was observed in individuals with limited (lSSc) and diffuse (dSSc) systemic Scleroderma compared to healthy controls. These findings suggest that loss of Csf1 in Pi16+ fibroblasts elicit changes in the population dynamics of skin macrophages and modifications to tissue architecture.

BackgroundLung ischemia-reperfusion (IR) injury drives early morbidity after lung transplantation and cardiothoracic surgery, yet targeted preventive therapies are lacking. The gut-lung axis and microbiota-derived tryptophan metabolites, including indole-3-propionate (IPA), may regulate pulmonary immunity and inflammation. We investigated whether a tryptophan-rich (Trp-Rich) diet attenuates sterile lung IR injury by increasing microbiota-derived indole metabolites and reprogramming alveolar macrophage (AM) inflammatory responses. MethodsC57BL/6 mice received isocaloric tryptophan-standard (Trp-Std; 0.18%) or Trp-Rich (0.60%) diets for 14 days, then underwent unilateral left lung IR (60 min ischemia followed by 60 min reperfusion). Oxygen saturation, lung cytokines, and aryl hydrocarbon receptor (AhR) signaling readouts (Cyp1a1/Cyp1b1) were evaluated. Gut microbiota was profiled by 16S rRNA sequencing, and targeted metabolomics quantified tryptophan metabolites in feces, portal vein (PV) plasma, and lung tissue. To further assess inflammatory priming in vivo, mice were additionally challenged with intratracheal lipopolysaccharide (LPS). Mechanistic studies compared IPA with related indole metabolites in MH-S cells and primary human AMs, including ex vivo nutritional IR, LPS stimulation, and AhR stimulation and blockade using synthetic agonists and antagonists. ResultsTrp-Rich feeding improved post-IR oxygenation, reduced lung IL-1{beta}, and increased pulmonary Cyp1a1/Cyp1b1 gene expression. Trp-Rich diet remodeled the gut microbiota, including enrichment of Bifidobacterium and Lactobacillus, and increased IPA levels across feces, PV plasma, and lung tissue, with lower kynurenine/IPA ratios across matrices. In the LPS intratracheal challenge, Trp-Rich feeding reduced IL-6 levels in lung tissue and systemic plasma. Primary murine AMs isolated from Trp-Rich mice also showed reduced IL-1{beta} and IL-6 release in an ex vivo nutritional IR model. Among tested indole metabolites, IPA showed the strongest dose-dependent suppression of LPS-induced cytokines and chemokines in MH-S cells and primary human AMs, remained active in the ex vivo nutritional IR model, and its anti-inflammatory effect was abrogated by AhR blockade and enhanced by co-treatment with other indole metabolites. ConclusionsA Trp-Rich diet attenuated sterile lung IR injury, coinciding with gut microbiota remodeling, increased systemic and pulmonary IPA, reduced inflammatory priming, and reprogrammed AM responses. These data support diet- or microbiome-directed strategies targeting IPA-AhR signaling to mitigate perioperative lung IR injury. Caption for graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=190 SRC="FIGDIR/small/714281v1_ufig1.gif" ALT="Figure 1"> View larger version (67K): org.highwire.dtl.DTLVardef@1b06a9corg.highwire.dtl.DTLVardef@1273f33org.highwire.dtl.DTLVardef@1a63a2borg.highwire.dtl.DTLVardef@350e1c_HPS_FORMAT_FIGEXP M_FIG A tryptophan-rich diet remodels the gut microbiota and indole metabolite profiles, including IPA, enhances alveolar macrophage AhR signaling, and attenuates sterile lung ischemia-reperfusion injury. C_FIG

ObjectivesCD4+ T cells play key roles in regulating immune responses during pregnancy, therefore we aimed to understand the CD4+ T cell surface proteome and transcriptome during pregnancy. MethodsCD4+ T cells were analysed in blood and decidua from term-pregnancies (>37 weeks), and non-pregnant blood. >350 surface proteins were screened via flow cytometry, and transcriptomes were analysed using single-cell RNA sequencing with >130 CITE-seq barcoded antibodies. ResultsSurface protein screening identified changes to ILT4/CD85d, CD9, IFN-{gamma} receptor {beta}-chain, CX3CR1 and CCR5 in the pregnant blood and decidual CD4+ T cells. CX3CR1 and CCR5 had the highest expression on the effector-memory T cell (TEM) subset in the blood, with expression consistent across subsets in decidua. CD126/IL-6R was lower in pregnant blood and decidual CD4+ T cells, while scRNAseq identified enrichment in the IL-6R signalling pathway in naive CD4+ T cells in pregnant blood. Both sIL-6R and IL-6 concentrations were increased in plasma during pregnancy, suggesting perturbations to the IL-6/IL-6R signalling axis. Meanwhile, decidual CD4+ T cells had increased expression of transcription factor RUNX3 in the CD69+ tissue-resident-like subset. ConclusionsOur findings demonstrate altered molecular expression in CD4+ T cells during pregnancy. This provides important mechanistic insight of their adaptation and regulation during placental development, which may drive placental dysfunction or pregnancy complications including preeclampsia, fetal growth restriction and stillbirth. These new data may inform future studies that focus on determining the significance of differentially- expressed immune features in pregnancy to identify potential targets for immune modulation to treat pregnancy complications and infections.

BackgroundHumans and mice display elevated levels of IL-27, an immunosuppressive cytokine shown to increase during neonatal bacterial sepsis and compromise survival. This study explores two hypotheses for regulation of IL-27 expression: 1) decreased DNA methylation in newborns that contributes to increased expression of IL-27 genes; 2) neonatal hormones regulate IL-27 expression through upstream hormone response elements (HREs). MethodsWhole genome methyl-seq analysis of neonatal and adult blood-derived macrophages identified differentially methylated regions (DMRs) at steady-state. Quantitative PCR (qPCR) measured expression of IL-27 genes (IL27p28 and EBI3) in human and murine neonatal macrophages stimulated in vitro with synthetic glucocorticoid or progesterone. Confocal microscopy and chromatin immunoprecipitation (ChIP) of glucocorticoid receptor (GR) assessed translocation into the nucleus and binding to the EBI3 promoter. ResultsThe IL-27p28 promoter contained DMRs that were increased in the neonatal cohort. The analysis did not identify DMRs within the EBI3 promoter. Dexamethasone stimulation increased EBI3 gene expression in human and murine neonatal macrophages. GR localized to the nucleus in response to dexamethasone and was enriched at the EBI3 upstream regulatory region. ConclusionThese data suggest glucocorticoid (GC) signaling increases EBI3 expression. This has importance in the context of antenatal GC administration that may increase IL-27 levels. Impact Statement{blacksquare} Elevated expression of IL-27 in early life impairs the host response to invasive bacterial infection in neonates. {blacksquare}Understanding the regulatory mechanisms contributing to increased IL-27 during the neonatal period is necessary to reduce susceptibility to infection in this vulnerable population. {blacksquare}The methylation status of the IL-27 genes in macrophages from neonatal and adult blood donors does not suggest regulation of differential expression with age. {blacksquare}Glucocorticoids are a signal that can induce EBI3 gene expression in a GR-dependent manner. {blacksquare}Glucocorticoid therapy for premature infants may increase IL-27 expression and promote enhanced susceptibility to infection.

Expression of the Csf1r gene in cells of the mononuclear phagocyte lineage is regulated by a conserved enhancer, the fms-intronic regulatory element (FIRE). In mice with a germ-line deletion of FIRE (Fireko) CSF1R expression is undetectable in bone marrow progenitors and classical monocytes. Fireko mice lack subpopulations of macrophages in the brain and periphery but develop normally. Here we show that loss of CSF1R expression in Fireko mice is partly overcome by CSF2 in vitro and inflammatory recruitment in vitro. Analysis of heterozygous mutant mice and deletion of the conserved AP1 motif in FIRE provide evidence that continuous receptor synthesis determines CSF1 responsiveness. The absence of macrophages in kidney and heart of Fireko mice was not associated with detectable loss of physiological function. In a model of renal injury macrophage recruitment and histopathology were similar in WT and Fireko mice. Tissue resident macrophages that were depleted in Fireko mice, including microglia, were replaced by donor-derived cells following intraperitoneal adoptive transfer of wild-type bone marrow at weaning. The Fireko mouse provides a novel platform to dissect the functions of tissue resident macrophages in development, homeostasis and pathology. Summary StatementThis study describes a unique model of selective tissue resident macrophage deficiency arising from dysregulated expression of the mouse Csf1r gene.

BackgroundChronic obstructive pulmonary disease (COPD) is a chronic lung condition characterised by accelerated lung aging. Extracellular vesicles (EVs), which can be categorised into large EVs (LEVs) and small EVs (SEVs), may play a critical role in intercellular communication. They contribute to the pathogenesis of COPD by transporting and transferring microRNAs (miRNAs). This study profiles cells and EV-associated miRNAs from both healthy and COPD small airway (SA)-epithelial cells and SA-fibroblasts and identifies the biological pathways associated with these miRNAs. MethodsEVs were isolated from conditioned media of healthy and COPD SA-epithelial cells and SA-fibroblasts, both at baseline and following H2O2 exposure. MiRNAs were extracted from cells and EVs and analysed by small RNA (smRNA) sequencing. ResultsSmRNA sequencing of COPD SA-epithelial cells and EVs revealed that four miRNAs were upregulated and fourteen were downregulated in the cells compared to healthy controls. COPD LEVs displayed nine upregulated and ten downregulated miRNAs, while SEVs showed ten upregulated and eleven downregulated miRNAs. Only one miRNA consistently upregulated in COPD SA-epithelial cells, LEVs, and SEVs. The various differentially expressed miRNAs were primarily associated with cellular senescence pathways. In SA-fibroblasts 39 miRNAs were upregulated in COPD compared to healthy cells. 14 miRNAs were upregulated in COPD LEVs and 11 downregulated, whereas SEVs exhibited twenty upregulated and eleven downregulated miRNAs. Overlap was limited, with only three miRNAs consistently upregulated in SA-fibroblasts and EVs. These miRNAs were linked to pathways related to fibrosis and cellular senescence. Furthermore, oxidative stress alters the miRNA profiles detected in cells and EVs differently between cells from healthy individuals and COPD patients. ConclusionsCOPD alters miRNA signatures in cells and their EVs, with limited overlap between compartments. These COPD-associated miRNAs are enriched in pathways driving cellular senescence and fibrosis, suggesting a potential role in disease progression.

Equine asthma (EA) is a highly prevalent, chronic, inflammatory disease of the lower airways ranging from mild-to-moderate to severe clinical presentations. Diagnosis currently relies on bronchoalveolar lavage fluid (BALF) cytology, an invasive method associated with interobserver variability, which highlights the need for more reproducible approaches. MicroRNAs (miRNAs) are small noncoding RNAs involved in post-transcriptional gene regulation. They are stable and readily detectable in body fluids and have shown promising results as biomarkers in human asthma. The aim of this study was to characterize miRNA abundance profiles in BALF and serum from horses with distinct EA endotypes to evaluate their biomarker potential and explore their involvement in disease pathogenesis. A total of 43 horses were included and classified as either EA (n=32) or controls (n=11), based on clinical examination and BALF cytology. The EA horses were further divided into three endotypes based on BALF inflammatory cell composition: neutrophilic asthma (n=10), mastocytic asthma (n=15), and mixed asthma (n=7). RNA was isolated from both serum and BALF samples and analyzed by quantitative real-time PCR (qPCR) targeting 103 miRNAs linked to asthma and pulmonary inflammation in humans. Differential miRNA abundance was analyzed across EA endotypes. The most significantly differentially abundant miRNAs were used for in silico target prediction and pathway enrichment analyses. Horses with mixed EA had significantly lower levels of eca-miR-125a-3p and eca-miR-125b-5p in BALF compared to controls. Additionally, eca-miR-146a-5p abundance was significantly increased in BALF from horses with neutrophilic EA compared to mastocytic EA. Target and pathway enrichment analyses for eca-miR-146a-5p identified immune-relevant pathways, such as MAPK and T-cell receptor signaling, supporting its involvement in inflammatory processes associated with asthma. This study identified three promising candidates, eca-miR-125a-3p, eca-miR-125b-5p, and eca-miR-146a-5p, as potential biomarkers associated with different EA endotypes. These miRNAs are interesting candidates for further investigation in an independent cohort.

Lymph nodes (LN) are key secondary lymphoid organs (SLO) for a coordinated immune response. They have been extensively characterized by numerous investigative techniques chiefly as single cell suspensions because they are composed of vagile yet crowded hematolymphoid elements, unfriendly to spatial tissue organization-saving techniques. We comprehensively classify in situ all cells of 19 human LN free of pathology with a 78-marker antibody panel, an hyperplexed cyclic staining method, MILAN, and an analytical bioinformatic pipeline, BRAQUE. A total of 77 cell types were classified, encompassing T, B, innate immune and stromal cells. CD4 and CD8 T-cells were classified into 27 unique subsets by leveraging the expression profiles of TCF7, the presence of co-inhibitory receptors and the spatial distribution. CD5 and TCF7 expression defined novel B-cell types. CD27+ mature B-cells occupied previously unrecognized nodal spaces non-overlapping with the cortex and the plasma-cell rich medullary cords. Type 2 conventional dendritic cells were located in nodular paracortical aggregates. Statistically controlled pairwise neighborhood analysis showed sparse cell-cell interactions, known and new neighbors, established and novel LN landscape niches. A high-dimensional proteomic interrogation of the normal human LN provides spatial allocation of known cell types, novel interactions and the landscape organization.

Early skin inflammation requires coordinated immune regulation, with neutrophils acting as first-line responders. While the blood vasculature and its role in neutrophil recruitment during infection has been extensively studied, the lymphatic system remains comparatively understudied despite its known role in immune cell trafficking. Growing evidence suggests lymphatic vessels actively participate in regulating inflammatory responses, yet whether they coordinate neutrophil behavior during skin infection remains unclear. Staphylococcus aureus is particularly problematic in this context, employing multiple immune evasion strategies and representing a major driver of antibiotic-resistant skin and soft tissue infections worldwide. To address this gap, we developed a human-based 3D microphysiological system incorporating luminal lymphatic endothelial vessels, a collagen matrix and bacteria to model an infected microenvironment. We evaluated neutrophil migration, phagocytosis and NETosis in response to Escherichia coli and S. aureus. Lymphatic endothelium amplified neutrophil migration in a bacterial-dependent manner, with E. coli promoting directional migration toward the vessel while S. aureus suppressed migration and directionality despite increased phagocytic uptake. S. aureus also induced myeloperoxidase-positive NETs with nuclear morphology consistent with vital NETosis, rescued by DNase treatment. To our knowledge, this is the first demonstration that lymphatic endothelium directly drives neutrophil behavior during skin infection.

The bone marrow haematopoietic niche is composed of a diverse array of cell types and extracellular matrix components that together support healthy haematopoiesis. However, live imaging of the bone marrow microenvironment is hampered by tissue accessibility limitations. Using intravital imaging through a titanium imaging window, we investigated the dynamics of human haematopoietic cells and mesenchymal stromal cells within an ectopically implanted humanised scaffold in an immunodeficient murine host. These cell populations expand and differentiate over time, accompanied by progressive remodelling of the scaffold. We observe migration of murine endothelial cells into the scaffold, leading to the formation of a vascular network during the initial development of the humanised niche. Subsequently, the dense collagen matrix that makes up the implanted niche is altered and larger gaps form in regions populated by mesenchymal stroma cells. Collectively, our findings demonstrate dynamic remodelling of the extracellular milieu that supports haematopoietic cell development and establish a platform for longitudinal, in vivo investigation of these processes. Altogether, we describe a novel model that aligns with the 3R guiding principles and enables real-time assessment of bone marrow cell dynamics in vivo. Summary statementRatcliffe and Mian et al. image in vivo dynamics of a bone marrow haematopoietic niche model.

ObjectivesTransformative observations demonstrate unprecedented success of B cell-depleting interventions in many human autoimmune diseases, calling for a deeper understanding of the triggers leading to B cell-mediated autoimmunity and its perpetuation in human disease. Here, we investigated whether the autoreactive B cell response targeting human topoisomerase 1 (TOP1), a hallmark of systemic sclerosis, could cross-react with TOP1 of microbial origin. MethodsHomologies between human and microbial TOP1 were analyzed using Foldseek. TOP1-reactive monoclonal antibodies from patient-derived, human TOP1-reactive B cell receptors were generated and assessed for reactivity against human TOP1 and TOP1 from a prototypic yeast, Saccharomyces cerevisiae (S. cerevisiae). Reactivity of polyclonal serum IgG from anti-TOP1 autoantibody (ATA)+, anti-centromere autoantibody (ACA)+ SSc patients and healthy donors (HDs) was tested. Finally, B cell lines were generated expressing human ATA to study B cell activation upon antigenic stimulation. ResultsStructural homologues of human TOP1 were found in many microbes, particularly in fungi. Taking TOP1 from S. cerevisiae as a prototype, microbial TOP1 was recognized by polyclonal patient IgG and by several monoclonal ATAs. Importantly, S. cerevisiae TOP1 also activated B cells expressing a patient-derived, human TOP1-reactive B cell receptor. Patients affected by interstitial lung disease most frequently showed recognition of microbial TOP1. ConclusionsThese findings identify fungi as potential drivers of immune dysregulation in human autoimmunity, specifically in SSc, highlighting microbial antigen cross-reactive cells as important therapeutic targets. Moreover, these data provide first functional evidence for a breach of B cell tolerance against human TOP1 triggered by cross-reactivity to fungal TOP1.

To explore the mechanism of Hsa_circ_0000629 adsorbing miR-212-5p/ nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) through sponge in bronchial asthma. Twenty BALB/C mice were randomly divided into a normal control group and an asthma group. Pathological changes in lung tissue were observed via HE staining. Human bronchial epithelial cells (16HBE) were transfected with Hsa_circ_0000629 overexpression group (Hsa_circ_0000629-over), Hsa_circ_0000629 siRNA (Hsa_circ_0000629-si), mimic NC, miR-212-5p mimic, inhibitor NC, miR-212-5p inhibitor, and LPS+Hsa_circ_0000629 si. LPS-induced asthmatic cell models (LPS group) and untransfected 16HBE cells (NC group) served as controls. qRT-PCR was used to measure Hsa_circ_0000629, miR-212-5p and NLRP3 expression. ELISA assessed interleukin 18 (IL-18), interleukin 1{beta} (IL-1{beta}), interleukin 6 (IL-6) and tumor necrosis factor - (TNF-) levels. Cell proliferation and the apoptosis were evaluated by EDU assay and flow cytometry, respectively. Western blot analyzed Cleaved-caspase 1, 3 and 9 proteins expression. Dual-luciferase assay verified the binding sites of Hsa_circ_0000629 to miR-212-5p and NLRP3 to miR-212-5p. HE staining revealed inflammatory cell infiltration, bronchial wall thickening, smooth muscle hyperplasia, and alveolar destruction in asthmatic mice. Compared with the controls, Hsa_circ_0000629 and NLRP3 expression were significantly increased, while miR-212-5p expression was decreased in asthmatic lung tissues. In 16HBE cells, Hsa_circ_0000629-over and LPS groups showed elevated Hsa_circ_0000629 and NLRP3 expression but reduced miR-212-5p levels. Silencing Hsa_circ_0000629 in LPS-treated cells (LPS+Hsa_circ_0000629-si) reversed these effects. Overexpression of miR-212-5p counteracted Hsa_circ_0000629-induced NLRP3 upregulation, while miR-212-5p inhibition enhanced NLRP3 expression. LPS exposure increased TNF-, IL-18, IL-6, and IL-1{beta} levels, reduced cell proliferation, and promoted apoptosis. These changes were attenuated by Hsa_circ_0000629 silencing or miR-212-5p overexpression. Western blot confirmed that Hsa_circ_0000629 overexpression upregulated Cleaved-Caspase 1, 3, and 9, whereas miR-212-5p mimic or Hsa_circ_0000629-si reversed this trend. Dual-luciferase assays demonstrated targeted interactions among Hsa_circ_0000629, miR-212-5p, and NLRP3. Interference with Hsa_circ_0000629 expression can alleviate LPS induced apoptosis in 16HBE cells and inhibit the expression of inflammatory factors by targeting the miR-212-5p/NLRP pathway, which may be a new target for the treatment of asthma.

In mammals, most of the iron is found in the heme of red blood cells (RBCs), which must be recycled to support erythropoiesis in the bone marrow. Splenic red pulp macrophages (RPMs) play a crucial role in this process by phagocytosing senescent RBCs, metabolizing the heme and releasing iron back into the blood. Free cytoplasmic iron generates toxic reactive oxygen species, yet iron-specific adaptations of RPMs are not well documented. We previously reported that autophagy prevents ferroptosis in Langerhans cells, a cutaneous phagocyte subset. Thus, we hypothesized that autophagy may be important for the regulation of RPM metabolism and their maintenance of systemic iron homeostasis. To study this, we used Atg5flox/flox and Cd169cre mouse models to delete ATG5 in CD169+ macrophages, including RPMs. Atg5-deficient RPMs were decreased in number, and the remaining ones showed increased generation of toxic lipid peroxides. Spleens of Atg5{Delta}Cd169 mice were enlarged and contained more RBCs. Finally, autophagy impairment in RPMs exacerbated RBC loss in a model of phenylhydrazine-induced anemia. Our findings exemplify how dysregulation of macrophage metabolism alters their function and can disrupt tissue homeostasis upon challenge.

BackgroundIdiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease characterized by aberrantly activated, apoptosis-resistant profibrotic lung (myo)fibroblasts. Prior research has demonstrated that lung fibroblasts from patients with IPF exhibit resistance to DNA damage, suggesting that this behavior contributes to their persistent survival and continuous proliferation. We propose that elevated levels of the DNA damage repair protein RAD51 regulate myofibroblast activation and apoptosis and provide a potential therapeutic target to impede fibrosis progression. MethodsHuman lung fibroblasts were transfected with siRNA against RAD51 or treated with RAD51-specific inhibitor B02 and markers of fibrosis, DNA damage, apoptosis, metabolic reprogramming, and mitochondrial dynamics were assessed. The preclinical efficacy of B02 was evaluated in human precision cut lung slices (PCLS) and in a mouse model of pulmonary fibrosis. FindingsRAD51 expression was significantly upregulated in the lungs and lung fibroblasts of IPF patients. Knockdown or inhibition of RAD51 in fibroblasts reduced profibrotic marker expression, suppressed mTORC1 signaling and mitochondrial function, and increased apoptosis susceptibility. Pharmacological inhibition of RAD51 shifted the profibrotic phenotype towards a fibrosis-resolving state in human and mouse PCLS, and in a bleomycin-induced mouse model of lung fibrosis. InterpretationThe inhibition of RAD51 exerts therapeutic benefits in lung fibrosis by promoting apoptosis. Our findings identify that inhibiting RAD51 with B02 in fibroblasts impairs DNA repair and induces metabolic reprogramming, making it a potential therapeutic target. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSPulmonary fibrosis (PF) is characterized by excessive fibroblast activation and subsequent deposition of extracellular matrix (ECM) proteins, which ultimately disrupt normal lung architecture. A significant contributing factor to the pathogenesis of pulmonary fibrosis is the presence of fibroblasts that are resistant to apoptosis, preventing normal wound healing. Recent studies highlight the DNA repair protein RAD51 as effective in protecting fibroblasts from death induced by chemotherapy and ionizing radiation. These finding suggested that RAD51 could have a role in fibroblast activation and apoptosis resistance in pulmonary fibrosis. Added value of this studyWe demonstrated that RAD51 is important for maintaining apoptosis-resistant fibrotic fibroblasts and their metabolic abnormalities. Our findings indicated that TGF{beta}-mediated upregulation of RAD51 reduces DNA damage, activates multiple pathways related to fibroblast activation and proliferation, and induces metabolic reprogramming, ultimately regulating apoptosis. Mechanistically, RAD51 inhibition enhanced p53 acetylation at lysine 120 and upregulated the expression proapoptotic proteins PUMA/BAK in mitochondria, promoting apoptosis. Pharmacological inhibition of RAD51 using the specific inhibitor B02 during the fibrotic phase of experimental lung disease effectively ameliorated pulmonary fibrosis. Implications of all the available evidenceOur findings establish that RAD51 plays an important role in the survival of apoptosis-resistant fibrotic fibroblasts. We propose that reducing RAD51 expression leads to the metabolic reprogramming of activated fibroblasts, resulting in decreased mitochondrial respiration, reduced ATP levels, and diminished glycolysis or glutaminolysis. These observations suggest that targeting energy metabolism through RAD51 inhibition could be a viable strategy to enhance apoptosis, thereby creating a therapeutically targetable pathway in fibrotic cells. These findings highlight the potential of RAD51 as a therapeutic target for the treatment of IPF.

Asthma is a chronic respiratory illness that causes mild to severe inflammation throughout narrowed airways. During allergic airways inflammation, autophagy prevents extensive lung tissue impairment while inducing a protective anti-pathogen response and macrophages in the lung to maintain homeostasis. Previous studies of autophagy genes and asthma have shown an association with variants in ATG5, but a comprehensive analysis of autophagy related genes and asthma has not been performed. Here we utilize summary statistic data generated from a two-stage genome-wide association study (GWAS) of asthma in the UK Biobank. We examined variants in 21 autophagy related genes and found statistically significant associations for 28 variants in two genes in the discovery dataset and nominally significant replication for 16 of these variants, all annotated to ATG4B. This is the first evidence of an association with variants in ATG4B with asthma which provides a novel potential for future drug development.