αvβ8 integrin-expression by BATF3-dependent dendritic cells facilitates early IgA responses to Rotavirus

Stat5b/Ezh2 axis governs high PD-L1 expressing tolerogenic dendritic cell subset in autoimmune diabetes

Dendritic cells (DCs) are specialized antigen-presenting cells that play an important role in inducing and maintaining immune tolerance. The altered distribution and/or function of DCs contributes to defective tolerance in autoimmune diseases such as type 1 diabetes (T1D). In human T1D and in NOD mouse models, DCs share some defects and are often described as less tolerogenic and excessively immunogenic. In the NOD mouse model, the autoimmune response is associated with a defect in the Stat5b signaling pathway. We have reported that expressing a constitutively active form of Stat5b in DCs of transgenic NOD mice (NOD.Stat5b-CA), re-established their tolerogenic function, restored autoimmune tolerance and conferred protection from diabetes. However, the role and molecular mechanisms of Stat5b signaling in regulating splenic conventional DCs tolerogenic signature remained unclear. In this study, we reported that, compared to immunogenic splenic DCs of NOD, splenic DCs of NOD.Stat5b-CA mice exhibited a tolerogenic profile marked by elevated PD-L1 and PD-L2 expression, reduced pro-inflammatory cytokine production, increased frequency of the cDC2 subset and decreased frequency of the cDC1 subset. This tolerogenic profile was associated with increased Ezh2 and IRF4 but decreased IRF8 expression. We also found an upregulation of PD-L1 in the cDC1 subset and high PD-L1 and PD-L2 expression in cDC2 of NOD.Stat5b-CA mice. Mechanistically, we demonstrated that Ezh2 plays an important role in the maintenance of high PD-L1 expression in cDC1 and cDC2 subsets and that Ezh2 inhibition resulted in PD-L1 but not PD-L2 downregulation which was more drastic in the cDC2 subset. Additionally, Ezh2 inhibition severely reduced the cDC2 subset and increased the cDC1 subset and Stat5b-CA.DC pro-inflammatory cytokine production. Together our data suggest that the Stat5b-Ezh2 axis is critical for the maintenance of tolerogenic high PD-L1-expressing cDC2 and autoimmune tolerance in NOD.Stat5b-CA mice.

Probiotics induce intestinal IgA secretion in weanling mice potentially through promoting intestinal APRIL expression and modulating the gut microbiota composition

Intestinal infections are strongly associated with infant mortality, and intestinal immunoglobulin A (IgA) is important to protect infants from intestinal infections after weaning. This study aims to screen probiotics that can promote the production of intestinal IgA after weaning and further explore their potential mechanisms of action. In this study, probiotics promoting intestinal IgA production were screened in weanling mouse models. The results showed that oral administration of Bifidobacterium bifidum (B. bifidum) FL228.1 and Bifidobacterium bifidum (B. bifidum) FL276.1 significantly enhanced IgA levels in the small intestine and upregulated the expression of a proliferation-inducing ligand (APRIL) and its upstream regulatory factor toll-like receptor 4 (TLR4). Furthermore, B. bifidum FL228.1 upregulated the relative abundance of Lactobacillus, while B. bifidum FL276.1 increased the relative abundance of Marvinbryantia and decreased Mucispirillum, further elevating intestinal IgA levels. In summary, B. bifidum FL228.1 and B. bifidum FL276.1 can induce IgA production in the intestinal tract of weanling mice by promoting intestinal APRIL expression and mediating changes in the gut microbiota, thus playing a significant role in enhancing local intestinal immunity in infants.

Concise review: The heterogenous roles of BATF3 in cancer oncogenesis and dendritic cells and T cells differentiation and function considering the importance of BATF3-dependent dendritic cells

The transcription factor, known as basic leucine zipper ATF-like 3 (BATF3), is a crucial contributor to the development of conventional type 1 dendritic cells (cDC1), which is definitely required for priming CD8 + T cell-mediated immunity against intracellular pathogens and malignancies. In this respect, BATF3-dependent cDC1 can bring about immunological tolerance, an autoimmune response, graft immunity, and defense against infectious agents such as viruses, microbes, parasites, and fungi. Moreover, the important function of cDC1 in stimulating CD8 + T cells creates an excellent opportunity to develop a highly effective target for vaccination against intracellular pathogens and diseases. BATF3 has been clarified to control the development of CD8α+ and CD103+ DCs. The presence of BATF3-dependent cDC1 in the tumor microenvironment (TME) reinforces immunosurveillance and improves immunotherapy approaches, which can be beneficial for cancer immunotherapy. Additionally, BATF3 acts as a transcriptional inhibitor of Treg development by decreasing the expression of the transcription factor FOXP3. However, when overexpressed in CD8 + T cells, it can enhance their survival and facilitate their transition to a memory state. BATF3 induces Th9 cell differentiation by binding to the IL-9 promoter through a BATF3/IRF4 complex. One of the latest research findings is the oncogenic function of BATF3, which has been approved and illustrated in several biological processes of proliferation and invasion.

Gut-associated lymphoid tissue: a microbiota-driven hub of B cell immunity

The diverse gut microbiota, which is associated with mucosal health and general wellbeing, maintains gut-associated lymphoid tissues (GALT) in a chronically activated state, including sustainment of germinal centers in a context of high antigenic load. This influences the rules for B cell engagement with antigen and the potential consequences. Recent data have highlighted differences between GALT and other lymphoid tissues. For example, GALT propagates IgA responses against glycans that show signs of having been generated in germinal centers. Other findings suggest that humans are among those species where GALT supports the diversification, propagation, and possibly selection of systemic B cells. Here, we review novel findings that identify GALT as distinctive, and able to support these processes.

Mast cells help organize the Peyer's patch niche for induction of IgA responses

Peyer's patches (PPs) are lymphoid structures situated adjacent to the intestinal epithelium that support B cell responses that give rise to many intestinal IgA-secreting cells. Induction of isotype switching to IgA in PPs requires interactions between B cells and TGFβ-activating conventional dendritic cells type 2 (cDC2s) in the subepithelial dome (SED). However, the mechanisms promoting cDC2 positioning in the SED are unclear. Here, we found that PP cDC2s express GPR35, a receptor that promotes cell migration in response to various metabolites, including 5-hydroxyindoleacetic acid (5-HIAA). In mice lacking GPR35, fewer cDC2s were found in the SED, and frequencies of IgA+ germinal center (GC) B cells were reduced. IgA plasma cells were reduced in both the PPs and lamina propria. These phenotypes were also observed in chimeric mice that lacked GPR35 selectively in cDCs. GPR35 deficiency led to reduced coating of commensal bacteria with IgA and reduced IgA responses to cholera toxin. Mast cells were present in the SED, and mast cell-deficient mice had reduced PP cDC2s and IgA+ cells. Ablation of tryptophan hydroxylase 1 (Tph1) in mast cells to prevent their production of 5-HIAA similarly led to reduced PP cDC2s and IgA responses. Thus, mast cell-guided positioning of GPR35+ cDC2s in the PP SED supports induction of intestinal IgA responses.

APOE4 impairs the microglial response in Alzheimer's disease by inducing TGFβ-mediated checkpoints

The APOE4 allele is the strongest genetic risk factor for late-onset Alzheimer's disease (AD). The contribution of microglial APOE4 to AD pathogenesis is unknown, although APOE has the most enriched gene expression in neurodegenerative microglia (MGnD). Here, we show in mice and humans a negative role of microglial APOE4 in the induction of the MGnD response to neurodegeneration. Deletion of microglial APOE4 restores the MGnD phenotype associated with neuroprotection in P301S tau transgenic mice and decreases pathology in APP/PS1 mice. MGnD-astrocyte cross-talk associated with β-amyloid (Aβ) plaque encapsulation and clearance are mediated via LGALS3 signaling following microglial APOE4 deletion. In the brains of AD donors carrying the APOE4 allele, we found a sex-dependent reciprocal induction of AD risk factors associated with suppression of MGnD genes in females, including LGALS3, compared to individuals homozygous for the APOE3 allele. Mechanistically, APOE4-mediated induction of ITGB8-transforming growth factor-β (TGFβ) signaling impairs the MGnD response via upregulation of microglial homeostatic checkpoints, including Inpp5d, in mice. Deletion of Inpp5d in microglia restores MGnD-astrocyte cross-talk and facilitates plaque clearance in APP/PS1 mice. We identify the microglial APOE4-ITGB8-TGFβ pathway as a negative regulator of microglial response to AD pathology, and restoring the MGnD phenotype via blocking ITGB8-TGFβ signaling provides a promising therapeutic intervention for AD.

Select symbionts drive high IgA levels in the mouse intestine

Immunoglobulin A (IgA) is an important factor in maintaining homeostasis at mucosal surfaces, yet luminal IgA levels vary widely. Total IgA levels are thought to be driven by individual immune responses to specific microbes. Here, we found that the prebiotic, pectin oligosaccharide (pec-oligo), induced high IgA levels in the small intestine in a T cell-dependent manner. Surprisingly, this IgA-high phenotype was retained after cessation of pec-oligo treatment, and microbiome transmission either horizontally or vertically was sufficient to retain high IgA levels in the absence of pec-oligo. Interestingly, the bacterial taxa enriched in the overall pec-oligo bacterial community differed from IgA-coated microbes in this same community. Rather, a group of ethanol-resistant microbes, highly enriched for Lachnospiraceae bacterium A2, drove the IgA-high phenotype. These findings support a model of intestinal adaptive immunity in which a limited number of microbes can promote durable changes in IgA directed to many symbionts.

Radial glia promote microglial development through integrin αVβ8 -TGFβ1 signaling

Microglia diversity emerges from interactions between intrinsic genetic programs and environment-derived signals, but how these processes unfold and interact in the developing brain remains unclear. Here, we show that radial glia-expressed integrin beta 8 (ITGB8) expressed in radial glia progenitors activates microglia-expressed TGFβ1, permitting microglial development. Domain-restricted deletion of Itgb8 in these progenitors establishes complementary regions with developmentally arrested "dysmature" microglia that persist into adulthood. In the absence of autocrine TGFβ1 signaling, we find that microglia adopt a similar dysmature phenotype, leading to neuromotor symptoms almost identical to Itgb8 mutant mice. In contrast, microglia lacking the TGFβ signal transducers Smad2 and Smad3 have a less polarized dysmature phenotype and correspondingly less severe neuromotor dysfunction. Finally, we show that non-canonical (Smad-independent) signaling partially suppresses disease and development associated gene expression, providing compelling evidence for the adoption of microglial developmental signaling pathways in the context of injury or disease.

Establishment of isotype-switched, antigen-specific B cells in multiple mucosal tissues using non-mucosal immunization

Although most pathogens infect the human body via mucosal surfaces, very few injectable vaccines can specifically target immune cells to these tissues where their effector functions would be most desirable. We have previously shown that certain adjuvants can program vaccine-specific helper T cells to migrate to the gut, even when the vaccine is delivered non-mucosally. It is not known whether this is true for antigen-specific B cell responses. Here we show that a single intradermal vaccination with the adjuvant double mutant heat-labile toxin (dmLT) induces a robust endogenous, vaccine-specific, isotype-switched B cell response. When the vaccine was intradermally boosted, we detected non-circulating vaccine-specific B cell responses in the lamina propria of the large intestines, Peyer's patches, and lungs. When compared to the TLR9 ligand adjuvant CpG, only dmLT was able to drive the establishment of isotype-switched resident B cells in these mucosal tissues, even when the dmLT-adjuvanted vaccine was administered non-mucosally. Further, we found that the transcription factor Batf3 was important for the full germinal center reaction, isotype switching, and Peyer's patch migration of these B cells. Collectively, these data indicate that specific adjuvants can promote mucosal homing and the establishment of activated, antigen-specific B cells in mucosal tissues, even when these adjuvants are delivered by a non-mucosal route. These findings could fundamentally change the way future vaccines are formulated and delivered.

The Interplay between Integrins and Immune Cells as a Regulator in Cancer Immunology

Integrins are a group of heterodimers consisting of α and β subunits that mediate a variety of physiological activities of immune cells, including cell migration, adhesion, proliferation, survival, and immunotolerance. Multiple types of integrins act differently on the same immune cells, while the same integrin may exert various effects on different immune cells. In the development of cancer, integrins are involved in the regulation of cancer cell proliferation, invasion, migration, and angiogenesis; conversely, integrins promote immune cell aggregation to mediate the elimination of tumors. The important roles of integrins in cancer progression have provided valuable clues for the diagnosis and targeted treatment of cancer. Furthermore, many integrin inhibitors have been investigated in clinical trials to explore effective regimens and reduce side effects. Due to the complexity of the mechanism of integrin-mediated cancer progression, challenges remain in the research and development of cancer immunotherapies (CITs). This review enumerates the effects of integrins on four types of immune cells and the potential mechanisms involved in the progression of cancer, which will provide ideas for more optimal CIT in the future.

IgA Nephropathy: Current Understanding and Perspectives on Pathogenesis and Targeted Treatment

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide, with varied clinical and histopathological features between individuals, particularly across races. As an autoimmune disease, IgAN arises from consequences of increased circulating levels of galactose-deficient IgA1 and mesangial deposition of IgA-containing immune complexes, which are recognized as key events in the widely accepted "multi-hit" pathogenesis of IgAN. The emerging evidence further provides insights into the role of genes, environment, mucosal immunity and complement system. These developments are paralleled by the increasing availability of diagnostic tools, potential biomarkers and therapeutic agents. In this review, we summarize current evidence and outline novel findings in the prognosis, clinical trials and translational research from the updated perspectives of IgAN pathogenesis.

A RORγt+ cell instructs gut microbiota-specific Treg cell differentiation

The mutualistic relationship of gut-resident microbiota and the host immune system promotes homeostasis that ensures maintenance of the microbial community and of a largely non-aggressive immune cell compartment^1,2. The consequences of disturbing this balance include proximal inflammatory conditions, such as Crohn's disease, and systemic illnesses. This equilibrium is achieved in part through the induction of both effector and suppressor arms of the adaptive immune system. Helicobacter species induce T regulatory (T_reg) and T follicular helper (T_FH) cells under homeostatic conditions, but induce inflammatory T helper 17 (T_H17) cells when induced T_reg (iT_reg) cells are compromised^3,4. How Helicobacter and other gut bacteria direct T cells to adopt distinct functions remains poorly understood. Here we investigated the cells and molecular components required for iT_reg cell differentiation. We found that antigen presentation by cells expressing RORγt, rather than by classical dendritic cells, was required and sufficient for induction of T_reg cells. These RORγt⁺ cells-probably type 3 innate lymphoid cells and/or Janus cells⁵-require the antigen-presentation machinery, the chemokine receptor CCR7 and the TGFβ activator α_v integrin. In the absence of any of these factors, there was expansion of pathogenic T_H17 cells instead of iT_reg cells, induced by CCR7-independent antigen-presenting cells. Thus, intestinal commensal microbes and their products target multiple antigen-presenting cells with pre-determined features suited to directing appropriate T cell differentiation programmes, rather than a common antigen-presenting cell that they endow with appropriate functions.

A self-sustaining layer of early-life-origin B cells drives steady-state IgA responses in the adult gut

The adult immune system consists of cells that emerged at various times during ontogeny. We aimed to define the relationship between developmental origin and composition of the adult B cell pool during unperturbed hematopoiesis. Lineage tracing stratified murine adult B cells based on the timing of output, revealing that a substantial portion originated within a restricted neonatal window. In addition to B-1a cells, early-life time-stamped B cells included clonally interrelated IgA plasma cells in the gut and bone marrow. These were actively maintained by B cell memory within gut chronic germinal centers and contained commensal microbiota reactivity. Neonatal rotavirus infection recruited recurrent IgA clones that were distinct from those arising by infection with the same antigen in adults. Finally, gut IgA plasma cells arose from the same hematopoietic progenitors as B-1a cells during ontogeny. Thus, a complex layer of neonatally imprinted B cells confer unique antibody responses later in life.

New perspectives on the regulation of germinal center reaction via αvβ8- mediated activation of TGFβ

Transforming growth factor-β (TGFβ) is a long-known modulator of immune responses but has seemingly contradictory effects on B cells. Among cytokines, TGFβ has the particularity of being produced and secreted in a latent form and must be activated before it can bind to its receptor and induce signaling. While the concept of controlled delivery of TGFβ signaling via αvβ8 integrin-mediated activation has gained some interest in the field of mucosal immunity, the role of this molecular mechanism in regulating T-dependent B cell responses is just emerging. We review here the role of TGFβ and its activation, in particular by αvβ8 integrin, in the regulation of mucosal IgA responses and its demonstrated and putative involvement in regulating germinal center (GC) B cell responses. We examine both the direct effect of TGFβ on GC B cells and its ability to modulate the functions of helper cells, namely follicular T cells (Tfh and Tfr) and follicular dendritic cells. Synthetizing recently published works, we reconcile apparently conflicting data and propose an innovative and unified view on the regulation of the GC reaction by TGFβ, highlighting the role of its activation by αvβ8 integrin.

Rotavirus-Induced Expansion of Antigen-Specific CD8 T Cells Does Not Require Signaling via TLR3, MyD88 or the Type I Interferon Receptor

Rotavirus (RV) infection induces strong adaptive immunity. While protection from reinfection requires humoral immunity, initial clearance of infection depends on cytotoxic CD8 T cells. Type I classical dendritic cells (cDC1) excel at CD8 T cell induction through cross-presentation and are essential for optimal cytotoxicity towards RV. Upon sensing of infection-induced innate immune signals through pattern recognition receptors (PRRs), cumulating in autocrine type I interferon (IFN) signaling, cDC1 mature and migrate to the draining lymph nodes (LNs), where they prime adaptive immune cells. To analyze which PRR pathways lead to robust cytotoxicity in the context of RV infection, we measured RV-specific CD8 T cell priming in mice deficient for Toll-like receptor 3 (TLR3), recognizing double-stranded RNA, or for MyD88, the adapter for all other TLRs and IL-1 family cytokines. Individual TLR3- and MyD88-mediated signaling was not required for the priming of CD8 T cell responses to RV and neither deficiency impacted on RV clearance. Surprisingly, the accumulation of RV-specific CD8 T cells was also not altered in the absence of type I IFN signaling, while their ability to produce IFNγ and granzyme were blunted. Together, this suggests a substantial level of redundancy in the sensing of RV infection and the translation of signals into protective CD8 T cell immunity.

Effects of Multispecies Probiotic on Intestinal Microbiota and Mucosal Barrier Function of Neonatal Calves Infected With E. coli K99

Altered gut microbiota are implicated in inflammatory neonatal calf diarrhea caused by E. coli K99. Beneficial probiotics are used to modulate gut microbiota. However, factors that mediate host-microbe interactions remain unclear. We evaluated the effects of a combination of multispecies probiotics (MSP) on growth, intestinal epithelial development, intestinal immune function and microbiota of neonatal calves infected with E. coli K99. Twelve newborn calves were randomly assigned as follows: C (control, without MSP); D (E. coli O78:K99 + gentamycin); and P (E. coli O78:K99 + supplemental MSP). All groups were studied for 21 d. MSP supplementation significantly (i) changed fungal Chao1 and Shannon indices of the intestine compared with group D; (ii) reduced the relative abundance of Bacteroides and Actinobacteria, while increasing Bifidobacteria, Ascomycetes, and Saccharomyces, compared with groups C and D; (iii) improved duodenal and jejunal mucosal SIgA and total Short Chain Fatty Acids (SCFA) concentrations compared with group D; (iv) increased relative ZO-1 and occludin mRNA expression in jejunal mucosa compared with group D; and (v) enhanced intestinal energy metabolism and defense mechanisms of calves by reducing HSP90 expression in E. coli K99, thereby alleviating the inflammatory response and promoting recovery of mucosal function. Our research may provide direct theoretical support for future applications of MSP in ruminant production.

Dendritic cell functions in the inductive and effector sites of intestinal immunity

The intestine is constantly exposed to foreign antigens, which are mostly innocuous but can sometimes be harmful. Therefore, the intestinal immune system has the delicate task of maintaining immune tolerance to harmless food antigens while inducing tailored immune responses to pathogens and regulating but tolerating the microbiota. Intestinal dendritic cells (DCs) play a central role in these functions as sentinel cells able to prime and polarize the T cell responses. DCs are deployed throughout the intestinal mucosa but with local specializations along the gut length and between the diffuse effector sites of the gut lamina propria (LP) and the well-organized immune inductive sites comprising isolated lymphoid follicles (ILFs), Peyer's patches (PPs), and other species-specific gut-associated lymphoid tissues (GALTs). Understanding the specificities of each intestinal DC subset, how environmental factors influence DC functions, and how these can be modulated is key to harnessing the therapeutic potential of mucosal adaptive immune responses, whether by enhancing the efficacy of mucosal vaccines or by increasing tolerogenic responses in inflammatory disorders. In this review, we summarize recent findings related to intestinal DCs in steady state and upon inflammation, with a special focus on their functional specializations, highly dependent on their microenvironment.

Novel antigen-presenting cell imparts Treg-dependent tolerance to gut microbiota

Establishing and maintaining tolerance to self-antigens or innocuous foreign antigens is vital for the preservation of organismal health. Within the thymus, medullary thymic epithelial cells (mTECs) expressing autoimmune regulator (AIRE) have a critical role in self-tolerance through deletion of autoreactive T cells and promotion of thymic regulatory T (T_reg) cell development^1-4. Within weeks of birth, a separate wave of T_reg cell differentiation occurs in the periphery upon exposure to antigens derived from the diet and commensal microbiota^5-8, yet the cell types responsible for the generation of peripheral T_reg (pT_reg) cells have not been identified. Here we describe the identification of a class of RORγt⁺ antigen-presenting cells called Thetis cells, with transcriptional features of both mTECs and dendritic cells, comprising four major sub-groups (TC I-TC IV). We uncover a developmental wave of Thetis cells within intestinal lymph nodes during a critical window in early life, coinciding with the wave of pT_reg cell differentiation. Whereas TC I and TC III expressed the signature mTEC nuclear factor AIRE, TC IV lacked AIRE expression and was enriched for molecules required for pT_reg generation, including the TGF-β-activating integrin αvβ8. Loss of either major histocompatibility complex class II (MHCII) or ITGB8 by Thetis cells led to a profound impairment in intestinal pT_reg differentiation, with ensuing colitis. By contrast, MHCII expression by RORγt⁺ group 3 innate lymphoid cells (ILC3) and classical dendritic cells was neither sufficient nor required for pT_reg generation, further implicating TC IV as the tolerogenic RORγt⁺ antigen-presenting cell with an essential function in early life. Our studies reveal parallel pathways for the establishment of tolerance to self and foreign antigens in the thymus and periphery, respectively, marked by the involvement of shared cellular and transcriptional programmes.

Regulatory T cells promote cancer immune-escape through integrin αvβ8-mediated TGF-β activation

Presence of TGFβ in the tumor microenvironment is one of the most relevant cancer immune-escape mechanisms. TGFβ is secreted in an inactive form, and its activation within the tumor may depend on different cell types and mechanisms than its production. Here we show in mouse melanoma and breast cancer models that regulatory T (Treg) cells expressing the β8 chain of αvβ8 integrin (Itgβ8) are the main cell type in the tumors that activates TGFβ, produced by the cancer cells and stored in the tumor micro-environment. Itgβ8 ablation in Treg cells impairs TGFβ signalling in intra-tumoral T lymphocytes but not in the tumor draining lymph nodes. Successively, the effector function of tumor infiltrating CD8+ T lymphocytes strengthens, leading to efficient control of tumor growth. In cancer patients, anti-Itgβ8 antibody treatment elicits similar improved cytotoxic T cell activation. Thus, this study reveals that Treg cells work in concert with cancer cells to produce bioactive-TGFβ and to create an immunosuppressive micro-environment.

Minor alterations in the intestinal microbiota composition upon Rotavirus infection do not affect susceptibility to DSS colitis

Viral triggers at the intestinal mucosa can have multiple global effects on intestinal integrity, causing elevated intestinal barrier strength and relative protection from subsequent inflammatory bowel disease (IBD) induction in various models. As viruses can interfere with the intestinal immune system both directly and indirectly through commensal bacteria, cause-effect relationships are difficult to define. Due to the complexity of putatively causative factors, our understanding of such virus-mediated protection is currently very limited. We here set out to better understand the impact that adult enteric infection with rotavirus (RV) might have on the composition of the intestinal microbiome and on the severity of IBD. We found that RV infection neither induced significant long-lasting microbiota community changes in the small or large intestine nor affected the severity of subsequent dextran sulfate sodium-induced colitis. Hence, adult murine RV infection does not exert lasting effects on intestinal homeostasis.

Rotavirus infection causes mesenteric lymph node hypertrophy independently of type I interferon or TNF-α in mice

Lymphoid organ hypertrophy is a characteristic feature of acute infection and is considered to enable efficient induction of adaptive immune responses. Accordingly, oral infection with rotavirus induced a robust increase in cellularity in the mesenteric LNs, whose kinetics correlated with viral load and was caused by halted lymphocyte egress and increased recruitment of cells without altered cellular proliferation. Lymphocyte sequestration and mesenteric LN hypertrophy were independent of type 1 IFN receptor signaling or the continuous presence of TNF-α. Our results support previous findings that adaptive immunity toward rotavirus is initiated primarily in the mesenteric LNs and show that type I IFN or TNF-α are not required to coordinate the events involved in the LN response.

Role of IgA in the early-life establishment of the gut microbiota and immunity: Implications for constructing a healthy start

Colonization and maturation of the gut microbiota (GM) during early life is a landmark event that fundamentally influences the (early) immunity and later-life health of various mammals. This is a delicate, systematic process that is biologically actively regulated by infants and their mothers, where (secretory) IgA, an important regulator of microbes found in breast milk and generated actively by infants, may play a key role. By binding to microbes, IgA can inhibit or enhance their colonization, influence their gene expression, and regulate immune responses. IgA dysfunction during early life is associated with disrupted GM maturation and various microbe-related diseases, such as necrotizing enterocolitis and diarrhea, which can also have a lasting effect on GM and host health. This review discusses the process of early GM maturation and its interaction with immunity and the role of IgA (focusing on milk secretory IgA) in regulating this process. The possible application of this knowledge in promoting normal GM maturation processes and immune education has also been highlighted.

Perspectives on how mucosal immune responses, infections and gut microbiome shape IgA nephropathy and future therapies

Infections have been considered to play a critical role in the pathogenesis of IgA nephropathy (IgAN) because synpharyngitic hematuria is a common feature in IgAN. However, how infections participate in this process is still debated. More recent studies have also revealed that the alteration of the gut microbiome exerts a profound effect on host immune responses, contributing to the etiology or progression of autoimmunity. Considering IgA as the first line of defense against bacterial and viral antigens, this review evaluates the relationships among intestinal infections, gut microbiome, and IgA for a better understanding of the pathogenesis of IgAN. Moreover, as a prototype of IgA immunity, we provide detailed clarification of IgAN pathogenesis to shed light on other diseases in which IgA plays a role. Finally, we discuss potential therapies focusing on microbes and mucosal immune responses in IgAN.