Antigen receptor signaling and cell death resistance controls intestinal humoral response zonation

Immunoglobulin A controls intestinal virus colonization to preserve immune homeostasis

Immunoglobulin A (IgA) is the predominant immunoglobulin isotype in mammals, primarily secreted at type I mucosal surfaces. Despite its abundance, the precise role of secretory IgA in the intestinal lumen, where it coats a diverse array of commensal microbiota, has remained elusive. Our study reveals that germinal center IgA responses are essential for preventing chronic colonization of the gut by specific viruses. In the absence of IgA, chronic viral colonization triggers an antigen-driven expansion of CD8αβ+ intraepithelial lymphocytes (IELs). Although these IELs are unable to clear the virus, they contribute to maintaining homeostasis by regulating its load and type I interferon responses. Consequently, IgA deficiency increases susceptibility to colitis in genetically susceptible hosts or following chemical induction but only in the presence of viral pathobionts requiring IgA for their clearance. These findings underscore the potential vulnerability of IgA-deficient individuals to immunopathology when exposed to selective viral pathobionts.

Yeast Cell Wall-Mediated Ileal Targeted Delivery System for IgA Nepharopathy Therapy

IgA nephropathy (IgAN) is a primary glomerulonephritis mediated by autoimmunity, characterized by an abnormal increase and the deposition of IgA in the glomeruli. In recent years, most studies have emphasized the crucial role of the gut-kidney axis in the pathogenesis of IgA nephropathy, and the ileal Peyer patches in the intestinal mucosal immune system are the main site for IgA production. Therefore, in this study, hydroxychloroquine (HCQ) and dexamethasone (DXM) were used as model drugs, and yeast cell wall (YCW)-coated oleic acid-grafted chitosan (CSO) was used as a carrier to construct a yeast cell wall oral drug delivery system HCQ/DXM@CSO@YCW. This delivery system achieves ileal targeted delivery through the yeast cell wall (YCW), reduces IgA production, and synergistically regulates the inflammatory pathological environment. The delivery system had good gastrointestinal stability and biocompatibility. In vitro cell experiments had shown the targeted uptake ability of dendritic cells and macrophages, and in vitro intestinal experiments showed that the YCW has ileal targeting properties. In vivo pharmacodynamic experiments showed that the HCQ/DXM@CSO@YCW delivery system could significantly reduce the serum IgA levels and IgA deposition in the renal tissue of IgAN mice, as well as the levels of IL-6, TNF-α, and TGF-β in the renal tissue, improving the pathological morphology of the renal tissue. Therefore, the DXM/HCQ@CSO@YCW oral administration system provided a new intestinal targeted delivery platform for intestinal mucosal immunotherapy in IgA nephropathy.

Gut IgA functionally interacts with systemic IgG to enhance antipneumococcal vaccine responses

The gut microbiota enhances systemic immunoglobulin G (IgG) responses to vaccines, but it is unknown whether this effect involves IgA, which coats intestinal microbes. That IgA may amplify postimmune IgG production is suggested by the impaired IgG response to pneumococcal vaccines in some IgA-deficient patients. Here, we found that antipneumococcal but not total IgG production was impaired in mice with IgA deficiency. The positive effect of gut IgA on antipneumococcal IgG responses started very early in life and could implicate gut bacteria, as these responses were attenuated in germ-free mice recolonized with gut microbes from IgA-deficient donors. IgA could exert this effect by constraining the systemic translocation of gut antigens, which was associated with chronic immune activation, including T cell overexpression of programmed cell death protein 1 (PD-1). This inhibitory receptor may attenuate antipneumococcal IgG production by causing B cell hyporesponsiveness, which improved upon anti-PD-1 treatment. Thus, gut IgA functionally interacts with systemic IgG to enhance antipneumococcal vaccine responses.

B cells in non-lymphoid tissues

B cells have long been understood to be drivers of both humoral and cellular immunity. Recent advances underscore this importance but also indicate that in infection, inflammatory disease and cancer, B cells function directly at sites of inflammation and form tissue-resident memory populations. The spatial organization and cellular niches of tissue B cells have profound effects on their function and on disease outcome, as well as on patient response to therapy. Here we review the role of B cells in peripheral tissues in homeostasis and disease, and discuss the newly identified cellular and molecular signals that are involved in regulating their activity. We integrate emerging data from multi-omic human studies with experimental models to propose a framework for B cell function in tissue inflammation and homeostasis.

Increased lamina propria B cells play roles in fructose-induced hypertension of Dahl salt-sensitive rats

AIMS

Although the immune system participates in the development of hypertension, the proportional contributions of distinct immune cells remain poorly understood. With the development of transcriptomics, we can profile the transcriptomes of individual immune cells and assess the relative contribution of each immune cell to the development of hypertension. So, we tested the hypothesis that increased lamina propria B cells play roles in fructose-induced hypertension of Dahl salt-sensitive (SS) rats.

MATERIALS AND METHODS

Eight-week-old Dahl SS and Dahl salt-resistant (SR) male rats were divided into four groups; each group received either tap water (TW) or a 20 % fructose solution (HFS) for 4 weeks. Systolic blood pressure was measured using the tail-cuff method. Single-cell RNA sequencing (scRNA-seq) analysis was performed on lamina propria (LP) cells and peripheral blood mononuclear cells (PBMCs) obtained from the SS and SR rats subjected to either TW or HFS.

KEY FINDINGS

Results revealed that high-fructose intake induced hypertension in the SS rats but not in the SR rats. It also increased B cells in LPs but not in PBMCs of the SS rats; their subsets showed increased follicular and naïve B cells. Increased lamina propria B cells play roles in fructose-induced hypertension of SS rats.

SIGNIFICANCE

This finding suggest that targeting B cells could be a potential strategy to mitigate high blood pressure in fructose-induced hypertension.

All roads lead to IgA: Mapping the many pathways of IgA induction in the gut

The increasing prevalence of food allergy and related pathologies in recent years has underscored the need to understand the factors affecting adverse reactions to food. Food allergy is caused when food-specific IgE triggers the release of histamine from mast cells. However, other food-specific antibody isotypes exist as well, including IgG and IgA. IgA is the main antibody isotype in the gut and mediates noninflammatory reactions to toxins, commensal bacteria, and food antigens. It has also been thought to induce tolerance to food, thus antagonizing the role of food-specific IgE. However, this has remained unclear as food-specific IgA generation is poorly understood. Particularly, the location of IgA induction, the role of T cell help, and the fates of food-specific B cells remain elusive. In this review, we outline what is known about food-specific IgA induction and highlight areas requiring further study. We also explore how knowledge of food-specific IgA induction can be informed by and subsequently contribute to our overall knowledge of gut immunity.

Gα13 restricts nutrient driven proliferation in mucosal germinal centers

Germinal centers (GCs) that form in mucosal sites are exposed to gut-derived factors that have the potential to influence homeostasis independent of antigen receptor-driven selective processes. The G-protein Gα13 confines B cells to the GC and limits the development of GC-derived lymphoma. We discovered that Gα13-deficiency fuels the GC reaction via increased mTORC1 signaling and Myc protein expression specifically in the mesenteric lymph node (mLN). The competitive advantage of Gα13-deficient GC B cells (GCBs) in mLN was not dependent on T cell help or gut microbiota. Instead, Gα13-deficient GCBs were selectively dependent on dietary nutrients likely due to greater access to gut lymphatics. Specifically, we found that diet-derived glutamine supported proliferation and Myc expression in Gα13-deficient GCBs in the mLN. Thus, GC confinement limits the effects of dietary glutamine on GC dynamics in mucosal tissues. Gα13 pathway mutations coopt these processes to promote the gut tropism of aggressive lymphoma.

Regulation of pulmonary plasma cell responses during secondary infection with influenza virus

During secondary infection with influenza virus, plasma cells (PCs) develop within the lung, providing a local source of antibodies. However, the site and mechanisms that regulate this process are poorly defined. Here, we show that while circulating memory B cells entered the lung during rechallenge and were activated within inducible bronchus-associated lymphoid tissues (iBALTs), resident memory B (BRM) cells responded earlier, and their activation occurred in a different niche: directly near infected alveoli. This process required NK cells but was largely independent of CD4 and CD8 T cells. Innate stimuli induced by virus-like particles containing ssRNA triggered BRM cell differentiation in the absence of cognate antigen, suggesting a low threshold of activation. In contrast, expansion of PCs in iBALTs took longer to develop and was critically dependent on CD4 T cells. Our work demonstrates that spatially distinct mechanisms evolved to support pulmonary secondary PC responses, and it reveals a specialized function for BRM cells as guardians of the alveoli.

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.

The NFκB signaling system in the generation of B-cell subsets: from germinal center B cells to memory B cells and plasma cells

Memory B cells and antibody-secreting cells are the two prime effector B cell populations that drive infection- and vaccine-induced long-term antibody-mediated immunity. The antibody-mediated immunity mostly relies on the formation of specialized structures within secondary lymphoid organs, called germinal centers (GCs), that facilitate the interactions between B cells, T cells, and antigen-presenting cells. Antigen-activated B cells may proliferate and differentiate into GC-independent plasmablasts and memory B cells or differentiate into GC B cells. The GC B cells undergo proliferation coupled to somatic hypermutation of their immunoglobulin genes for antibody affinity maturation. Subsequently, affinity mature GC B cells differentiate into GC-dependent plasma cells and memory B cells. Here, we review how the NFκB signaling system controls B cell proliferation and the generation of GC B cells, plasmablasts/plasma cells, and memory B cells. We also identify and discuss some important unanswered questions in this connection.