Project description:Tissue and microbial cues regulate the abundance and function of CD8+ T cells at barrier sites, yet the impact of specific microbes on their long-term durability remains unclear. Here, we show that the commensal protist Tritrichomonas musculus (T. mu) depletes intestinal CD8+ T cells, particularly tissue resident memory (TRM) cells, through activation of localized type 2 immunity. Colonization with T. mu or administration of its major secreted metabolite, succinate, led to the rapid decline of intestinal CD8+ T cells but left systemic memory T cells unaffected. The purinergic receptor, P2RX7, is highly expressed by intestinal TRMs and chemical antagonism of this receptor markedly restored CD8+ T cells during succinate feeding. Using lymphocytic choriomeningitis virus (LCMV) infection to track antigen-specific CD8+ memory T cells, we found viral-specific CD8+ TRMs repopulate the intestine independent of LCMV reinfection after removal of succinate treatment. These findings highlight how commensal protists and their metabolites reset homeostatic CD8+ T cell carrying capacity through damage-independent stimulation of TRM apoptosis and regulate mucosal memory.
Project description:Intestinal protists are emerging as key modulators of host immunity and microbial ecology, yet their roles remain poorly defined. Here, we investigated the role of two distinct protists, the amoeba Entamoeba muris, and the parabasalid, Tritrichomonas, to determine how they shape gut immunity in vivo individually and together. Unlike the well-characterized inducer of type 2 immunity, Tritrichomonas, which activates the tuft cell–IL-25–ILC2 circuit in the small intestine, E. muris failed to elicit robust immune responses in the intestine or colon. However, introduction of E. muris into mice naturally colonized by Tritrichomonas spp., or co-infection with E. muris and Tritrichomonas spp. suppressed the Tritrichomonas-induced type-2 response in the small intestine. Fecal and cecal qPCR suggest that E. muris may outcompete Tritrichomonas spp., with reduced protist loads in the cecum and possibly diminished succinate-driven tuft cell activation. We also identified sex-specific differences in the intestinal response to primary Tritrichomonas spp. colonization which have not previously been described. These findings reveal that E. muris can dampen existing type-2 immune circuits without triggering overt inflammation, underscoring its role as an immunomodulatory agent. This work provides a framework for understanding how commensal protists interact within the gut ecosystem and shape mucosal immunity in the absence of pathogenicity.
Project description:The ocular surface is colonized by commensal microbiota, which tune the local mucosal immune response. However, the mechanisms underlying the induction of an IL-17 response by γδ T cells in response to ocular commensal bacteria, particularly Corynebacterium mastitidis (C. mast), have not been fully investigated. Here, we demonstrated that intrinsic TLR2 activation in γδ T cells by commensal microbiota is required for their IL-17A production and fatty acid oxidation. We also identified IκBζ, a transcription factor whose expression is upregulated by TLR2 signaling, as a key regulator to enhance the expression of genes responsible for IL-17A production and FAO program. This study highlights the role of TLR2-mediated transcriptional regulation in targeting effector cytokines and metabolic programs to support IL-17A responses to commensal bacteria.
Project description:The ocular surface is colonized by commensal microbiota, which tune the local mucosal immune response. However, the mechanisms underlying the induction of an IL-17 response by γδ T cells in response to ocular commensal bacteria, particularly Corynebacterium mastitidis (C. mast), have not been fully investigated. Here, we demonstrated that intrinsic TLR2 activation in γδ T cells by commensal microbiota is required for their IL-17A production and fatty acid oxidation. We also identified IκBζ, a transcription factor whose expression is upregulated by TLR2 signaling, as a key regulator to enhance the expression of genes responsible for IL-17A production and FAO program. This study highlights the role of TLR2-mediated transcriptional regulation in targeting effector cytokines and metabolic programs to support IL-17A responses to commensal bacteria.
Project description:Immunoglobulin A (IgA) most predominant antibody isotype at mucosal surfaces and is regulated by both T cell-dependent (TD) and independent (TI) mechanisms. In the TD pathway, T follicular helper (TFH) cells provide help to B cells to generate high-affinity antibodies. T follicular regulatory (TFR) cells fine-tune antibody responses, but precisely how these cellsregulate microbiota-directed IgA at mucosal sites has been unclear. Here, we used a TFR-deficient mouse model (Foxp3Cre Bcl6fl/fl; Bcl6FC) in which the gut microbiota develops in the absence of TFR cells, while the broader regulatory T cell compartment remains intact. While Bcl6FC mice showed similar levels of IgA-coated commensal bacteria to wild-type mice in the naïve state, following oral immunization, Bcl6FC mice exhibited a durable increase in IgA-coated commensal bacteria in feces and small intestine, without changes in overall community composition or epithelial barrier permeability. IgA-seq analysis of Bcl6FC mice revealed an increased diversity of IgA-coated taxa, both in naïve and orally immunized mice. IgA coating index analysis, a measure of IgA affinity, identified higher IgA binding to multiple taxa in Bcl6C mice compared to control mice. Consistent with these findings, sera from immunized Bcl6FC mice showed increased IgA binding to Alloprevotella and Klebsiella species but not to E. coli or Group A/B Streptococcus compared to control mice. B cell receptor repertoire sequencing demonstrated divergent patterns of somatic hypermutation (SMH) for IgA and IgG, where TFR cells repressed IgA SMH but enhanced IgG somatic hypermutation. Mechanistically, suppression of commensal-directed IgA required TFR-derived IL-10 but was independent of CTLA-4. IL-10 directly inhibited TGF-β-driven IgA class switching of B cells in vitro. Together, our data identify TFR cells as critical gatekeepers of mucosal IgA responses, constraining commensal-specific IgA responses through a novel IL-10-dependent pathway. Our findings haveimportant implications for regulation of the microbiome by TFR cells and IgA.
Project description:The mammalian gut is inhabited by a large and complex microbial community that lives in a mutualistic relationship with its host. Innate and adaptive mucosal defense mechanisms ensure a homeostatic relationship with this commensal microbiota. Secretory antibodies are generated from the active polymeric Ig receptor (pIgR)-mediated transport of IgA and IgM antibodies to the gut lumen and form the first line of adaptive immune defense of the intestinal mucosa. We probed mucosal homeostasis in pIgR knockout (KO) mice, which lack secretory antibodies. We found that in pIgR KO mice, colonic epithelial cells, the cell type most closely in contact with intestinal microbes, differentially expressed (>2-fold change) more than 200 genes compared with wild type mice, and upregulated the expression of anti-microbial peptides in a commensal-dependent manner. Detailed profiling of microbial communities based on 16S rRNA genes revealed differences in the commensal microbiota between pIgR KO and wild type mice. Furthermore, we found that pIgR KO mice showed increased susceptibility to dextran sulfate sodium (DSS)-induced colitis, and that this was driven by their conventional intestinal microbiota. In conclusion, secretory antibodies or the pIgR itself are required to maintain a stable commensal microbiota. In the absence of these humoral effector components, gut homeostasis is disturbed and the outcome of colitis significantly worsened. 4 groups: wild type mice treated with antibiotic (5 replicates), wild type mice left untreated (5 replicates), pIgR KO mice treated with antibiotic (6 replicates), and pIgR KO mice left untreated (6 replicates).
Project description:Commensal bacteria influence host physiology, including immune responses, without invading host tissues. We show that proteins from segmented filamentous bacteria (SFB), which are immunomodulatory commensal microbes, are transferred into intestinal epithelial cells by adhesion-directed endocytosis that is distinct from the clathrin-dependent endocytosis of invasive pathogens. SFB transfer microbial cell wall-associated proteins, including an antigen that stimulates mucosal Th17 cell differentiation, into the cytosol of epithelial cells. Removal of CDC42 activity in vivo led to disruption of endocytosis induced by SFB, decreased epithelial antigen acquisition with consequent loss of immune modulation by SFB-specific CD4 T cells and mucosal Th17 cells. Our findings indicate direct communication between a resident gut microbe and the host and show that intestinal epithelial cells acquire antigens from commensal bacteria for generation of T-cell responses to the resident microbiota.