Fucoidan modulates gut microbiota and immunity in Peyer's patches against inflammatory bowel disease.

Although fucoidan has potential use as an anti-inflammatory agent, the specific mechanisms by which it influences signaling and immunomodulatory pathways between gut microbiota and Peyer's patches remain unclear. Therefore, the aim of this study was to investigate the therapeutic potential of fucoidan in a dextran sulfate sodium (DSS)-induced mouse model of inflammatory bowel disease (IBD) by examining the effects on gut microbiota and the underlying anti-inflammatory mechanisms. Purified fucoidan, which upon characterization revealed structural fragments comprising →3)-ß-D-Galp-(1→, →4)-α-L-Fucp-(1→, and →3)-α-L-Fucp-(1→ residues with a sulfation at position C2 was used. Treatment of the mice with fucoidan significantly alleviated the symptoms of IBD and restored the diversity of gut microbiota by enhancing the abundance of Bacteroidetes and reducing the proportion of Firmicutes. The administration of fucoidan also elevated levels of short-chain fatty acids while reducing the levels of pro-inflammatory cytokines, including interleukin (IL)-1ß, IL-6, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ. Most importantly, fucoidan attenuated the expression of integrin α4ß7/MAdCAM-1 and CCL25/CCR9, which are involved in homing intestinal lymphocytes within Peyer's patches. These findings indicate that fucoidan is a promising gut microbiota modulator and an anti-inflammatory agent for IBD.

Lrba participates in the differentiation of IgA+ B lymphocytes through TGFßR signaling.

Introduction: Lrba is a cytoplasmic protein involved in vesicular trafficking. Lrba-deficient (Lrba-/-) mice exhibit substantially higher levels of IgA in both serum and feces than wild-type (WT) mice. Transforming growth factor ß1 (TGFß1) and its receptors (TGFßR I and II) is essential for differentiating IgA+ B cells. Furthermore, increased IgA production suggests a potential connection between Lrba and the TGFßR signaling pathway in IgA production. However, the specific function of Lrba in B cell biology remains unknown. Aim: Given the increased IgA levels in Lrba-/- mice, the goal in this work was to explore the lymph organs where the switch to IgA occurs, and if TGFßR function is affected. Methods: Non-immunized Lrba-/- mice were compared with Lrba+/+ mice. IgA levels in the serum and feces, as well as during peripheral B cell development, were determined. IgA+ B cells and plasma cells were assessed in the small intestine and secondary lymphoid organs, such as the spleen, mesenteric lymph nodes, and Peyer's patches. The TGFßR signaling pathway was evaluated by determining the expression of TGFßR on B cells. Additionally, SMAD2 phosphorylation was measured under basal conditions and in response to recombinant TGFß. Finally, confocal microscopy was performed to investigate a possible interaction between Lrba and TGFßR in B cells. Results: Lrba-/- mice exhibited significantly higher levels of circulating IgA, IgA+ B, and plasma cells than in peripheral lymphoid organs those in WT mice. TGFßR expression on the membrane of B cells was similar in both Lrba-/- and Lrba+/+ mice. However, intracellular TGFßR expression was reduced in Lrba-/- mice. SMAD2 phosphorylation showed increased levels under basal conditions; stimulation with recombinant TGFß elicited a poorer response than in that in Lrba+/+ B cells. Finally, we found that Lrba colocalizes with TGFßR in B cells. Conclusion: Lrba is essential in controlling TGFßR signaling, subsequently regulating SMAD2 phosphorylation on B cells. This mechanism may explain the increased differentiation of IgA+ B cells and production of IgA-producing plasma cells.

Formation of the junctions between lymph follicles in the Peyer's patches even before postweaning activation.

Peyer's patches (PPs), which contain an abundance of B and T cells, play a key role in inducing pivotal immune responses in the intestinal tract. PPs are defined as aggregated lymph follicles, which consist of multiple lymph follicles (LFs) that may interact with each other in a synergistic manner. LFs are thought to be spherical in shape; however, the characteristics of their structure are not fully understood. To elucidate changes in the structure of PPs as individuals grow, we generated serial 2D sections from entire PPs harvested from mice at 2, 4, and 10 weeks of age and performed a 3D analysis using a software, Amira. Although the number of LFs in PPs was not changed throughout the experiment, the volume and surface area of LFs increased significantly, indicating that LFs in PPs develop continuously by recruiting immune cells, even after weaning. In response to the dramatic changes in the intestinal environment after weaning, the development of germinal centers (GCs) in LFs was observed at 4 and 10 weeks (but not 2 weeks) of age. In addition, GCs gradually began to form away from the center of LFs and close to the muscle layer where export lymphatic vessels develop. Importantly, each LF was joined to the adjacent LF; this feature was observed even in preweaning nonactivated PPs. These results suggest that PPs may have a unique organization and structure that enhance immune functions, allowing cells in LFs to have free access to adjacent LFs and egress smoothly from PPs to the periphery upon stimulation after weaning.

Peyer's Patch: Possible target for modulating the Gut-Brain-Axis through microbiota.

The gastrointestinal (GI) tract and the brain form bidirectional nervous, immune, and endocrine communications known as the gut-brain axis. Several factors can affect this axis; among them, various studies have focused on the microbiota and imply that alterations in microbiota combinations can influence both the brain and GI. Also, many studies have shown that the immune system has a vital role in varying gut microbiota combinations. In the current paper, we will review the multidirectional effects of gut microbiota, immune system, and nervous system on each other. Specifically, this review mainly focuses on the impact of Peyer's patches as a critical component of the gut immune system on the gut-brain axis through affecting the gut's microbial composition. In this way, some factors were discussed as proposed elements of missing gaps in this field.

Postbiotic-based recombinant receptor activator of NF-κB ligand enhanced oral vaccine efficiency in chicken.

Functional M cells are differentiated by receptor activator of NF-κB ligand (RANKL) and capture of luminal antigens to initiate immune responses. We aimed to use postbiotic-based recombinant chicken RANKL (cRANKL) to promote M cell differentiation and test the efficacy of oral vaccines. Chicks were divided into three groups that were administered phosphate-buffered saline (PBS), cell extracts of wild-type Lactococcus lactis subsp. lactis IL1403 (WT_CE), or cell extracts of recombinant L. lactis expressing cRANKL (cRANKL_CE). The expression of the M cell marker was measured, and the gut microbiome was profiled. The efficiency of the infectious bursal disease (IBD) vaccine was tested after 12 consecutive days of administering cRANKL_CE. The chickens that were administered cRANKL_CE (p = 0.038) had significantly higher Annexin A5 (ANXA5) mRNA expression levels than those in the PBS group (PBS vs. WT_CE, p = 0.657). In the gut microbiome analysis, no significant changes were observed. However, the relative abundance of Escherichia-Shigella was negatively correlated (r = - 0.43, p = 0.019) with ANXA5 mRNA expression in Peyer's patches. cRANKL_CE/IBD (p = 0.018) had significantly higher IBD-specific faecal IgA levels than PBS/IBD (PBS/IBD vs. WT_CE/IBD, p = 0.217). Postbiotic-based recombinant cRANKL effectively improved the expression of M cell markers and the efficiency of oral vaccines. No significant changes were observed in the gut microbiome after administration of postbiotic-based recombinant cRANKL. This strategy can be used for the development of feed additives and adjuvants. KEY POINTS: • Postbiotic-based recombinant cRANKL enhanced the expression of ANXA5 in chicken. • The relative abundance of Escherichia-Shigella was negatively correlated with ANXA5 expression. • Postbiotic-based recombinant cRANKL effectively improved the efficiency of oral vaccine.

Antigen-level resolution of commensal-specific B cell responses can be enabled by phage display screening coupled with B cell tetramers.

Induction of commensal-specific immunity contributes to tissue homeostasis, yet the mechanisms underlying induction of commensal-specific B cells remain poorly understood in part due to a lack of tools to identify these cells. Using phage display, we identified segmented filamentous bacteria (SFB) antigens targeted by serum and intestinal antibodies and generated B cell tetramers to track SFB-specific B cells in gut-associated lymphoid tissues. We revealed a compartmentalized response in SFB-specific B cell activation, with a gradient of immunoglobulin A (IgA), IgG1, and IgG2b isotype production along Peyer's patches contrasted by selective production of IgG2b within mesenteric lymph nodes. V(D)J sequencing and monoclonal antibody generation identified somatic hypermutation driven affinity maturation to SFB antigens under homeostatic conditions. Combining phage display and B cell tetramers will enable investigation of the ontogeny and function of commensal-specific B cell responses in tissue immunity, inflammation, and repair.

CD200R activation on naïve T cells by B cells induces suppressive activity of T cells via IL-24.

CD200 is an anti-inflammatory protein that facilitates signal transduction through its receptor, CD200R, in cells, resulting in immune response suppression. This includes reducing M1-like macrophages, enhancing M2-like macrophages, inhibiting NK cell cytotoxicity, and downregulating CTL responses. Activation of CD200R has been found to modulate dendritic cells, leading to the induction or enhancement of Treg cells expressing Foxp3. However, the precise mechanisms behind this process are still unclear. Our previous study demonstrated that B cells in Peyer's patches can induce Treg cells, so-called Treg-of-B (P) cells, through STAT6 phosphorylation. This study aimed to investigate the role of CD200 in Treg-of-B (P) cell generation. To clarify the mechanisms, we used wild-type, STAT6 deficient, and IL-24 deficient T cells to generate Treg-of-B (P) cells, and antagonist antibodies (anti-CD200 and anti-IL-20RB), an agonist anti-CD200R antibody, CD39 inhibitors (ARL67156 and POM-1), a STAT6 inhibitor (AS1517499), and soluble IL-20RB were also applied. Our findings revealed that Peyer's patch B cells expressed CD200 to activate the CD200R on T cells and initiate the process of Treg-of-B (P) cells generation. CD200 and CD200R interaction triggers the phosphorylation of STAT6, which regulated the expression of CD200R, CD39, and IL-24 in T cells. CD39 regulated the expression of IL-24, which sustained the expression of CD223 and IL-10 and maintained the cell viability. In summary, the generation of Treg-of-B (P) cells by Peyer's patch B cells was through the CD200R-STAT6-CD39-IL-24 axis pathway.

Characterization of intestinal mononuclear phagocyte subsets in young ruminants at homeostasis and during Cryptosporidium parvum infection.

Introduction: Cryptosporidiosis is a poorly controlled zoonosis caused by an intestinal parasite, Cryptosporidium parvum, with a high prevalence in livestock (cattle, sheep, and goats). Young animals are particularly susceptible to this infection due to the immaturity of their intestinal immune system. In a neonatal mouse model, we previously demonstrated the importance of the innate immunity and particularly of type 1 conventional dendritic cells (cDC1) among mononuclear phagocytes (MPs) in controlling the acute phase of C. parvum infection. These immune populations are well described in mice and humans, but their fine characterization in the intestine of young ruminants remained to be further explored. Methods: Immune cells of the small intestinal Peyer's patches and of the distal jejunum were isolated from naive lambs and calves at different ages. This was followed by their fine characterization by flow cytometry and transcriptomic analyses (q-RT-PCR and single cell RNAseq (lamb cells)). Newborn animals were infected with C. parvum, clinical signs and parasite burden were quantified, and isolated MP cells were characterized by flow cytometry in comparison with age matched control animals. Results: Here, we identified one population of macrophages and three subsets of cDC (cDC1, cDC2, and a minor cDC subset with migratory properties) in the intestine of lamb and calf by phenotypic and targeted gene expression analyses. Unsupervised single-cell transcriptomic analysis confirmed the identification of these four intestinal MP subpopulations in lamb, while highlighting a deeper diversity of cell subsets among monocytic and dendritic cells. We demonstrated a weak proportion of cDC1 in the intestine of highly susceptible newborn lambs together with an increase of these cells within the first days of life and in response to the infection. Discussion: Considering cDC1 importance for efficient parasite control in the mouse model, one may speculate that the cDC1/cDC2 ratio plays also a key role for the efficient control of C. parvum in young ruminants. In this study, we established the first fine characterization of intestinal MP subsets in young lambs and calves providing new insights for comparative immunology of the intestinal MP system across species and for future investigations on host-Cryptosporidium interactions in target species.

The immunological understanding on germinal center B cells in psoriasis.

The development of psoriasis is mainly driven by the dysregulation of T cells within the skin, marking a primary involvement of these cells in the pathogenesis. Although B cells are integral components of the immune system, their role in the initiation and progression of psoriasis is not as pivotal as that of T cells. The paradox of B cell suggests that, while it is crucial for adaptive immunity, B cells may contribute to the exacerbation of psoriasis. Numerous ideas proposed that there are potential relationships between psoriasis and B cells especially within germinal centers (GCs). Recent research projected that B cells might be triggered by autoantigens which then induced molecular mimicry to alter B cells activity within GC and generate autoantibodies and pro-inflammatory cytokines, form ectopic GC, and dysregulate the proliferation of keratinocytes. Hence, in this review, we gathered potential evidence indicating the participation of B cells in psoriasis within the context of GC, aiming to enhance our comprehension and advance treatment strategies for psoriasis thus inviting many new researchers to investigate this issue.

Migratory CD103+CD11b+ cDC2s in Peyer's patches are critical for gut IgA responses following oral immunization.

Induction and regulation of specific intestinal immunoglobulin (Ig)A responses critically depend on dendritic cell (DC) subsets and the T cells they activate in the Peyer's patches (PP). We found that oral immunization with cholera toxin (CT) as an adjuvant resulted in migration-dependent changes in the composition and localization of PP DC subsets with increased numbers of cluster of differentiation (CD)103- conventional DC (cDC)2s and lysozyme-expressing DC (LysoDCs) in the subepithelial dome and of CD103+ cDC2s that expressed CD101 in the T cell zones, while oral ovalbumin (OVA) tolerization was instead associated with greater accumulation of cDC1s and peripherally induced regulatory T cells (pTregs) in this area. Decreased IgA responses were observed after CT-adjuvanted immunization in huCD207DTA mice lacking CD103+ cDC2s, while oral OVA tolerization was inefficient in cDC1-deficient Batf3-/- mice. Using OVA transgenic T cell receptor CD4 T cell adoptive transfer models, we found that co-transferred endogenous wildtype CD4 T cells can hinder the induction of OVA-specific IgA responses through secretion of interleukin-10. CT could overcome this blocking effect, apparently through a modulating effect on pTregs while promoting an expansion of follicular helper T cells. The data support a model where cDC1-induced pTreg normally suppresses PP responses for any given antigen and where CT's oral adjuvanticity effect is dependent on promoting follicular helper T cell responses through induction of CD103+ cDC2s.

Integrated omics analysis reveals the immunologic characteristics of cystic Peyer's patches in the cecum of Bactrian camels.

Bactrian camels have specific mucosa-associated lymphoid tissue (MALT) throughout the large intestine, with species-unique cystic Peyer's patches (PPS) as the main type of tissue. However, detailed information about the molecular characteristics of PPS remains unclear. This study applied a transcriptomic analysis, untargeted metabolomics, and 16S rDNA sequencing to compare the significant differences between PPS and the adjacent normal intestine tissues (NPPS) during the healthy stage of three young Bactrian camels. The results showed that samples from PPS could be easily differentiated from the NPPS samples based on gene expression profile, metabolites, and microbial composition, separately indicated using dimension reduction methods. A total of 7,568 up-regulated and 1,266 down-regulated differentially expressed genes (DEGs) were detected, and an enrichment analysis found 994 DEGs that participated in immune-related functions, and a co-occurance network analysis identified nine hub genes (BTK, P2RX7, Pax5, DSG1, PTPN2, DOCK11, TBX21, IL10, and HLA-DOB) during multiple immunologic processes. Further, PPS and NPPS both had a similar pattern of most compounds among all profiles of metabolites, and only 113 differentially expressed metabolites (DEMs) were identified, with 101 of these being down-regulated. Deoxycholic acid (DCA; VIP = 37.96, log2FC = -2.97, P = 0), cholic acid (CA; VIP = 13.10, log2FC = -2.10, P = 0.01), and lithocholic acid (LCA; VIP = 12.94, log2FC = -1.63, P = 0.01) were the highest contributors to the significant dissimilarities between groups. PPS had significantly lower species richness (Chao1), while Firmicutes (35.92% ± 19.39%), Bacteroidetes (31.73% ± 6.24%), and Proteobacteria (13.96% ± 16.21%) were the main phyla across all samples. The LEfSe analysis showed that Lysinibacillus, Rikenellaceae_RC9_gut_group, Candidatus_Stoquefichus, Mailhella, Alistipes, and Ruminococcaceae_UCG_005 were biomarkers of the NPPS group, while Escherichia_Shigella, Synergistes, Pyramidobacter, Odoribacter, Methanobrevibacter, Cloacibacillus, Fusobacterium, and Parabacteroides were significantly higher in the PPS group. In the Procrustes analysis, the transcriptome changes between groups showed no significant correlations with metabolites or microbial communities, whereas the alteration of metabolites significantly correlated with the alteration of the microbial community. In the co-occurrence network, seven DEMs (M403T65-neg, M329T119-neg, M309T38-neg, M277T42-2-neg, M473T27-neg, M747T38-1-pos, and M482t187-pos) and 14 genera (e.g., Akkermansia, Candidatus-Stoquefichus, Caproiciproducens, and Erysipelatoclostridium) clustered much more tightly, suggesting dense interactions. The results of this study provide new insights into the understanding of the immune microenvironment of the cystic PPS in the cecum of Bactrian camels.

Peyer's patch TH17 cells are dispensable for gut IgA responses to oral immunization.

T helper 17 (TH17) cells located at the Peyer's patch (PP) inductive site and at the lamina propria effector site of the intestinal immune system are responsive to both pathogenic and commensal bacteria. Their plasticity to convert into follicular helper T (TFH) cells has been proposed to be central to gut immunoglobulin A (IgA) responses. Here, we used an IL-17A fate reporter mouse and an MHC-II tetramer to analyze antigen-specific CD4+ T cell subsets and isolate them for single-cell RNA sequencing after oral immunization with cholera toxin and ovalbumin. We found a TFH-dominated response with only rare antigen-specific TH17 cells (<8%) in the PP. A clonotypic analysis provided little support that clonotypes were shared between TFH and TH17 cells, arguing against TH17 plasticity as a major contributor to TFH differentiation. Two mouse models of TH17 deficiency confirmed that gut IgA responses to oral immunization do not require TH17 cells, with CD4CreRorcfl/fl mice exhibiting normal germinal centers in PP and unperturbed total IgA production in the intestine.

Engineered Nanoparticles inside a Microparticle Oral System for Enhanced Mucosal and Systemic Immunity.

Antigen delivery through an oral route requires overcoming multiple challenges, including gastrointestinal enzymes, mucus, and epithelial tight junctions. Although each barrier has a crucial role in determining the final efficiency of the oral vaccination, transcytosis of antigens through follicle-associated epithelium (FAE) represents a major challenge. Most of the research is focused on delivering an antigen to the M-cell for FAE transcytosis because M-cells can easily transport the antigen from the luminal site. However, the fact is that the M-cell population is less than 1% of the total gastrointestinal cells, and most of the oral vaccines have failed to show any effect in clinical trials. To challenge the current dogma of M-cell targeting, in this study, we designed a novel tandem peptide with a FAE-targeting peptide at the front position and a cell-penetrating peptide at the back position. The tandem peptide was attached to a smart delivery system, which overcomes the enzymatic barrier and the mucosal barrier. The result showed that the engineered system could target the FAE (enterocytes and M-cells) and successfully penetrate the enterocytes to reach the dendritic cells located at the subepithelium dome. There was successful maturation and activation of dendritic cells in vitro confirmed by a significant increase in maturation markers such as CD40, CD86, presentation marker MHC I, and proinflammatory cytokines (TNF-α, IL-6, and IL-10). The in vivo results showed a high production of CD4+ T-lymphocytes (helper T-cell) and a significantly higher production of CD8+ T-lymphocytes (killer T-cell). Finally, the production of mucosal immunity (IgA) in the trachea, intestine, and fecal extracts and systemic immunity (IgG, IgG1, and IgG2a) was successfully confirmed. To the best of our knowledge, this is the first study that designed a novel tandem peptide to target the FAE, which includes M-cells and enterocytes rather than M-cell targeting and showed that a significant induction of both the mucosal and systemic immune response was achieved compared to M-cell targeting.

Disrupted Peyer's Patch Microanatomy in COVID-19 Including Germinal Centre Atrophy Independent of Local Virus.

Confirmed SARS-coronavirus-2 infection with gastrointestinal symptoms and changes in microbiota associated with coronavirus disease 2019 (COVID-19) severity have been previously reported, but the disease impact on the architecture and cellularity of ileal Peyer's patches (PP) remains unknown. Here we analysed post-mortem tissues from throughout the gastrointestinal (GI) tract of patients who died with COVID-19. When virus was detected by PCR in the GI tract, immunohistochemistry identified virus in epithelium and lamina propria macrophages, but not in lymphoid tissues. Immunohistochemistry and imaging mass cytometry (IMC) analysis of ileal PP revealed depletion of germinal centres (GC), disruption of B cell/T cell zonation and decreased potential B and T cell interaction and lower nuclear density in COVID-19 patients. This occurred independent of the local viral levels. The changes in PP demonstrate that the ability to mount an intestinal immune response is compromised in severe COVID-19, which could contribute to observed dysbiosis.

Salmonella Uptake into Gut-Associated Lymphoid Tissues: Implications for Targeted Mucosal Vaccine Design and Delivery.

Peyer's patches are organized gut-associated lymphoid tissues (GALT) in the small intestine and the primary route by which particulate antigens, including viruses and bacteria, are sampled by the mucosal immune system. Antigen sampling occurs through M cells, a specialized epithelial cell type located in the follicle-associated epithelium (FAE) that overlie Peyer's patch lymphoid follicles. While Peyer's patches play an integral role in intestinal homeostasis, they are also a gateway by which enteric pathogens, like Salmonella enterica serovar Typhimurium (STm), cross the intestinal barrier. Once pathogens like STm gain access to the underlying network of mucosal dendritic cells and macrophages they can spread systemically. Thus, Peyer's patches are at the crossroads of mucosal immunity and intestinal pathogenesis. In this chapter, we provide detailed methods to assess STm entry into mouse Peyer's patch tissues. We describe Peyer's patch collection methods and provide strategies to enumerate bacterial uptake. We also detail a method for quantifying bacterial shedding from infected animals and provide an immunohistochemistry protocol for the localization of STm along the gastrointestinal tract and insight into pathogen transit in the presence of protective antibodies. While the protocols are written for STm, they are easily tailored to other enteric pathogens.

Muscarinic receptors control markers of inflammation in the small intestine of BALB/c mice.

Muscarinic-acetylcholine-receptors (mAChRs) modulate intestinal homeostasis, but their role in inflammation is unclear; thus, this issue was the focus of this study. BALB/c mice were treated for 7 days with muscarine (mAChR/agonist), atropine (mAChR/antagonist) or saline. Small-intestine samples were collected for histology and cytofluorometric assays in Peyer's patches (PP) and lamina propria (LP) cell-suspensions. In LP, goblet-cells/leukocytes/neutrophils/MPO+ cells and MPO/activity were increased in the muscarine group. In PP, IFN-γ+/CD4+ T or IL-6+/CD4+ T cell numbers were higher in the muscarine or atropine groups, respectively. In LP, TNF-α+/CD4+ T cell number was higher in the muscarine group and lower in the atropine.

Aging-Related Impairments to M Cells in Peyer's Patches Coincide With Disturbances to Paneth Cells.

The decline in mucosal immunity during aging increases susceptibility, morbidity and mortality to infections acquired via the gastrointestinal and respiratory tracts in the elderly. We previously showed that this immunosenescence includes a reduction in the functional maturation of M cells in the follicle-associated epithelia (FAE) covering the Peyer's patches, diminishing the ability to sample of antigens and pathogens from the gut lumen. Here, co-expression analysis of mRNA-seq data sets revealed a general down-regulation of most FAE- and M cell-related genes in Peyer's patches from aged mice, including key transcription factors known to be essential for M cell differentiation. Conversely, expression of ACE2, the cellular receptor for SARS-Cov-2 virus, was increased in the aged FAE. This raises the possibility that the susceptibility of aged Peyer's patches to infection with the SARS-Cov-2 virus is increased. Expression of key Paneth cell-related genes was also reduced in the ileum of aged mice, consistent with the adverse effects of aging on their function. However, the increased expression of these genes in the villous epithelium of aged mice suggested a disturbed distribution of Paneth cells in the aged intestine. Aging effects on Paneth cells negatively impact on the regenerative ability of the gut epithelium and could indirectly impede M cell differentiation. Thus, restoring Paneth cell function may represent a novel means to improve M cell differentiation in the aging intestine and increase mucosal vaccination efficacy in the elderly.

Intestinal CD11b+ B Cells Ameliorate Colitis by Secreting Immunoglobulin A.

The intestinal mucosal immune environment requires multiple immune cells to maintain homeostasis. Although intestinal B cells are among the most important immune cells, little is known about the mechanism that they employ to regulate immune homeostasis. In this study, we found that CD11b+ B cells significantly accumulated in the gut lamina propria and Peyer's patches in dextran sulfate sodium-induced colitis mouse models and patients with ulcerative colitis. Adoptive transfer of CD11b+ B cells, but not CD11b-/- B cells, effectively ameliorated colitis and exhibited therapeutic effects. Furthermore, CD11b+ B cells were found to produce higher levels of IgA than CD11b- B cells. CD11b deficiency in B cells dampened IgA production, resulting in the loss of their ability to ameliorate colitis. Mechanistically, CD11b+ B cells expressed abundant TGF-ß and TGF-ß receptor II, as well as highly activate phosphorylated Smad2/3 signaling pathway, consequently promoting the class switch to IgA. Collectively, our findings demonstrate that CD11b+ B cells are essential intestinal suppressive immune cells and the primary source of intestinal IgA, which plays an indispensable role in maintaining intestinal homeostasis.

IL-4-Producing Vγ1+/Vδ6+ γδ T Cells Sustain Germinal Center Reactions in Peyer's Patches of Mice.

The mucosal immune system is the first line of defense against pathogens. Germinal centers (GCs) in the Peyer's patches (PPs) of the small intestine are constantly generated through stimulation of the microbiota. In this study, we investigated the role of γδ T cells in the GC reactions in PPs. Most γδ T cells in PPs localized in the GCs and expressed a TCR composed of Vγ1 and Vδ6 chains. By using mice with partial and total γδ T cell deficiencies, we found that Vγ1+/Vδ6+ T cells can produce high amounts of IL-4, which drives the proliferation of GC B cells as well as the switch of GC B cells towards IgA. Therefore, we conclude that γδ T cells play a role in sustaining gut homeostasis and symbiosis via supporting the GC reactions in PPs.

The cholesterol metabolite 25-hydroxycholesterol restrains the transcriptional regulator SREBP2 and limits intestinal IgA plasma cell differentiation.

Diets high in cholesterol alter intestinal immunity. Here, we examined how the cholesterol metabolite 25-hydroxycholesterol (25-HC) impacts the intestinal B cell response. Mice lacking cholesterol 25-hydroxylase (CH25H), the enzyme generating 25-HC, had higher frequencies of immunoglobulin A (IgA)-secreting antigen-specific B cells upon immunization or infection. 25-HC did not affect class-switch recombination but rather restrained plasma cell (PC) differentiation. 25-HC was produced by follicular dendritic cells and increased in response to dietary cholesterol. Mechanistically, 25-HC restricted activation of the sterol-sensing transcription factor SREBP2, thereby regulating B cell cholesterol biosynthesis. Ectopic expression of SREBP2 in germinal center B cells induced rapid PC differentiation, whereas SREBP2 deficiency reduced PC output in vitro and in vivo. High-cholesterol diet impaired, whereas Ch25h deficiency enhanced, the IgA response against Salmonella and the resulting protection from systemic bacterial dissemination. Thus, a 25-HC-SREBP2 axis shapes the humoral response at the intestinal barrier, providing insight into the effect of high dietary cholesterol in intestinal immunity.