IgA Class Switch Recombination Research Articles

TGF-β1 impairs IgA class switch recombination and production in porcine Peyer's patches B cells.

Secretory IgA is crucial for preventing the invasion of entero-pathogens via intestinal mucosa. While it is well-established that Transforming growth factor β1 (TGF-β1) regulates IgA production in human and mouse B cells, our previous investigation revealed different functions of TGF-β1 in IgA generation in pigs compared with humans and mice, with the underlying mechanism remaining elusive. In this study, IgM+ B cells from porcine Peyer's patches (PPs) were isolated and stimulated with recombinant porcine TGF-β1 to evaluate the effect of TGF-β1 on pigs. The results showed that antibody production from B cells of PPs was impaired by TGF-β1 ex vivo. Furthermore, TGF-β1 treatment led to a decrease in the expression of germ-line transcript αand postswitch transcript α. Moreover, we observed that TGF-β1 predominantly inhibited the phosphorylation of p38-mitogen-activated protein kinases (MAPK), confirming the involvement of the p38-MAPK pathway in porcine IgA generation and IgA class switch recombination. The application of p38-MAPK inhibitor resulted in decreased B-cell differentiation levels. Collectively, this study demonstrates that exogenous TGF-β1 restrains the production and class switch recombination of IgA antibodies by inhibiting p38-MAPK signaling in porcine PPs B cells, which may constitute a component of TGF-β1-mediated inhibition of B-cell activation.

Mycobiota-induced IgA antibodies regulate fungal commensalism in the gut and are dysregulated in Crohn's disease.

Secretory immunoglobulin A (sIgA) plays an important role in gut barrier protection by shaping the resident microbiota community, restricting the growth of bacterial pathogens, and enhancing host protective immunity via immunological exclusion. Here, we found that a portion of microbiota-driven sIgA response is induced by and directed towards intestinal fungi. Analysis of the human gut mycobiota bound by sIgA revealed a preference for hyphae; a fungal morphotype associated with virulence. C. albicans was a potent inducer of IgA class switch recombination (CSR) among plasma cells, through an interaction dependent on intestinal phagocytes and hyphal programming. Characterization of sIgA affinity and polyreactivity showed that hyphae-associated virulence factors were bound by these antibodies and that sIgA influenced C. albicans morphotypes in the murine gut. Furthermore, an increase of granular hyphal morphologies in Crohn’s Disease (CD) patients compared to healthy controls, correlated with a decrease of antifungal sIgA antibody titers with affinity to hyphae-associated virulence factors. Thus, in addition to their importance in gut bacterial regulation, sIgA targets the uniquely fungal phenomenon of hyphal formation. Our findings indicate that antifungal sIgA produced in the gut can play a role in regulating intestinal fungal commensalism by coating fungal morphotypes linked to virulence, thereby providing a protective mechanism that might be dysregulated in CD patients.

Interleukin (IL)-21 Promotes the Differentiation of IgA-Producing Plasma Cells in Porcine Peyer's Patches via the JAK-STAT Signaling Pathway.

Secretory IgA is critical to prevent the invasion of pathogens via mucosa. However, the key factors and the mechanisms of IgA generation in the porcine gut are not well-understood. In this study, a panel of factors, including BAFF, APRIL, CD40L, TGF-β1, IL-6, IL-10, IL-17A, and IL-21, were employed to stimulate IgM+ B lymphocytes from porcine ileum Peyer's patches. The results showed that IL-21 significantly upregulated IgA production of B cells and facilitated cell proliferation and differentiation of antibody-secreting cells. In addition, three transcripts in porcine IgA class switch recombination (CSR), germ-line transcript α, post-switch transcript α, and circle transcript α, were first amplified by (nest-)PCR and sequenced. All these key indicators of IgA CSR were upregulated by IL-21 treatment. Furthermore, we found that IL-21 predominantly activated JAK1, STAT1, and STAT3 proteins and confirmed that the JAK-STAT signaling pathway was involved in porcine IgA CSR. Thus, IL-21 plays an important role in the proliferation and differentiation of IgA-secreting cells in porcine Peyer's patches through the JAK-STAT signaling pathway. These findings provide insights into the mucosal vaccine design by regulation of IL-21 for the prevention and control of enteric pathogens in the pig industry.

Longan Pulp Polysaccharide Protects Systemic Immunity and Intestinal Immunity in Mice Induced by Cyclophosphamide

Abstract Objectives This study aimed to explore the effect of longan pulp polysaccharide (LP) on the systemic immunity and intestinal mucosal immunity with immunosuppressive mice. The synthesis processing and secretion of intestinal secretory IgA (SIgA) were investigated. Methods Serum IgA, IgG, IgM and intestinal SIgA were detected by ELISA. Genes involved in the synthesis and secretion of SIgA were detected by Q-PCR and western blot. Results LP increased the thymus index, spleen index, and serum IgA level in cyclophosphamide (CTX)-treated mice. SIgA secretion in intestinal lumen was increased by LP as well. The underlying mechanism comes down to the facts as follows: LP increased intestinal cytokines expression and TGFβRII that is associated with pathways of IgA class switch recombination (CSR). By improving protein expression of mucosal address in cell-adhesion molecule-1 (MAdCAM-1) and integrin α4β7, LP was beneficial to gut homing of IgA + plasma cells. LP increased IgA, polymeric immunoglobulin receptor (pIgR), and secretory component (SC) to fortify the SIgA secretion. Conclusions This study suggested that moderate consumption of LP is helpful for improving systemic immunity and intestinal mucosal immunity via promotion of intestinal SIgA to strengthen the mucosal barrier. Funding Sources This work was supported by the National Key Research Project of China (2018YFC1602105, 2019YFD1002304), Guangdong Provincial Science and Technology Project (2018A050506050), President Foundation of Guangdong Academy of Agricultural Sciences (201812B).

Effect of Class Switch Recombination Defect on the Phenotype of Ataxia-Telangiectasia Patients

ABSTRACT Objectives: Ataxia-telangiectasia (A-T) is an autosomal recessive neurodegenerative disorder with multisystem involvement caused by homozygous or compound heterozygous mutations in the ataxia telangiectasia mutated (ATM) gene which encodes a serine/threonine protein kinase. The aims of this study were to investigate class switch recombination (CSR) and to review the clinical and immunologic phenotypes of 3 groups of A-T patients, including A-T patients with CSR defects (CSR-D), A-T patients with selective immunoglobulin A deficiency (IgA-D) and A-T patients with normal Ig level. Methods: In this study, 41 patients with confirmed diagnosis of A-T (16 A-T patients with HIgM, 15 A-T patients with IgA-D, and 10 A-T patients with normal Ig levels) from Iranian immunodeficiency registry center were enrolled. B-cell proliferation, in vitro CSR toward IgE and IgA were compared between three groups as well as G2 radiosensitivity assay. Results: Earliest presentation of telangiectasia was a significant hallmark in A-T patients with CSR-D (p = .036). In this investigation, we found that the frequency of respiratory infection (p = .002), pneumonia (p = .02), otitis media (p = .008), chronic fever (p < .001), autoimmunity (p = .02) and hepatosplenomegaly (p = .03) in A-T patients with HIgM phenotype were significantly higher than the other groups. As expected IgE production stimulation and IgA CSR were perturbed in HIgM patients that were aligned with the higher readiosenstivity scores in this group. Conclusion: A-T patients with HIgM compared to other A-T patients presenting more infections and noninfectious complications, therefore, early detection and careful management of these patients is necessary.

Effects of senataxin and RNA exosome on B-cell chromosomal integrity.

Loss of function of senataxin (SETX), a bona-fide RNA/DNA helicase, is associated with neuronal degeneration leading to Ataxia and Ocular Apraxia (AOA) in human patients. SETX is proposed to promote transcription termination, DNA replication, DNA repair, and to unwind deleterious RNA:DNA hybrids in the genome. In all the above-mentioned mechanisms, SETX unwinds transcription complex-associated nascent RNA which is then degraded by the RNA exosome complex. Here we have used B cells isolated from a SETX mutant mouse model and compared genomic instability and immunoglobulin heavy chain locus (IgH) class switch recombination (CSR) to evaluate aberrant and programmed genomic rearrangements, respectively. Similar to RNA exosome mutant primary B cells, SETX mutant primary B cells display genomic instability but a modest decrease in efficiency of CSR. Furthermore, knockdown of Setx mRNAs from CH12–F3 B-cell lines leads to a defect in IgA CSR and accumulation of aberrant patterns of mutations in IgH switch sequences. Given that SETX mutant mice do not recapitulate the AOA neurodegenerative phenotype, it is possible that some aspects of SETX biology are rescued by redundant helicases in mice. Overall, our study provides new insights into the role of the SETX/RNA exosome axis in suppressing genomic instability so that programmed DNA breaks are properly orchestrated.

Noncoding RNA transcription alters chromosomal topology to promote isotype-specific class switch recombination.

B cells undergo two types of genomic alterations to increase antibody diversity: introduction of point mutations into immunoglobulin heavy- and light-chain (IgH and IgL) variable regions by somatic hypermutation (SHM) and alteration of antibody effector functions by changing the expressed IgH constant region exons through IgH class switch recombination (CSR). SHM and CSR require the B cell-specific activation-induced cytidine deaminase (AID) protein, the transcription of germline noncoding RNAs, and the activity of the 3' regulatory region (3'RR) super-enhancer. Although many transcription regulatory elements (e.g., promoters and enhancers) reside inside the IgH and IgL sequences, the question remains whether clusters of regulatory elements outside IgH control CSR. Using RNA exosome-deficient mouse B cells where long noncoding RNAs (lncRNAs) are easily detected, we identified a cluster of three RNA-expressing elements that includes lncCSRIgA (that expresses lncRNA-CSRIgA). B cells isolated from a mouse model lacking lncRNA-CSRIgA transcription fail to undergo normal levels of CSR to IgA both in B cells of the Peyer's patches and grown in ex vivo culture conditions. lncRNA-CSRIgA is expressed from an enhancer site (lncCSRIgA ) to facilitate the recruitment of regulatory proteins to a nearby CTCF site (CTCFlncCSR) that alters the chromosomal interactions inside the TADlncCSRIgA and long-range interactions with the 3'RR super-enhancer. Humans with IgA deficiency show polymorphisms in the lncCSRIgA locus compared with the normal population. Thus, we provide evidence for an evolutionarily conserved topologically associated domain (TADlncCSRIgA) that coordinates IgA CSR in Peyer's patch B cells through an lncRNA (lncRNA-CSRIgA) transcription-dependent mechanism.

Class-switch recombination to IgA in the Peyer's patches requires natural thymus-derived Tregs and appears to be antigen independent.

Our understanding of how class-switch recombination (CSR) to IgA occurs in the gut is still incomplete. Earlier studies have indicated that Tregs are important for IgA CSR and these cells were thought to transform into follicular helper T cells (Tfh), responsible for germinal center formation in the Peyer's patches (PP). Following adoptive transfer of T-cell receptor-transgenic (TCR-Tg) CD4 T cells into nude mice, we unexpectedly found that oral immunization did not require an adjuvant to induce strong gut IgA and systemic IgG responses, suggesting an altered regulatory environment in the PP. After sorting of splenic TCR-Tg CD4 T cells into CD25+ or CD25- cells we observed that none of these fractions supported a gut IgA response, while IgG responses were unperturbed in mice receiving the CD25- cell fraction. Hence, while Tfh functions resided in the CD25- fraction the IgA CSR function in the PP was dependent on CD25+ Foxp3+ Tregs, which were found to be Helios+ neuropilin-1+ thymus-derived Tregs. This is the first study to demonstrate that Tfh and IgA CSR functions are indeed, unique, and separate functions in the PP with the former being TCR-dependent while the latter appeared to be antigen independent.

Endonuclease and redox activities of human apurinic/apyrimidinic endonuclease 1 have distinctive and essential functions in IgA class switch recombination

The base excision repair (BER) pathway is an important DNA repair pathway and is essential for immune responses. In fact, it regulates both the antigen-stimulated somatic hypermutation (SHM) process and plays a central function in the process of class switch recombination (CSR). For both processes, a central role for apurinic/apyrimidinic endonuclease 1 (APE1) has been demonstrated. APE1 acts also as a master regulator of gene expression through its redox activity. APE1's redox activity stimulates the DNA-binding activity of several transcription factors, including NF-κB and a few others involved in inflammation and in immune responses. Therefore, it is possible that APE1 has a role in regulating the CSR through its function as a redox coactivator. The present study was undertaken to address this question. Using the CSR-competent mouse B-cell line CH12F3 and a combination of specific inhibitors of APE1's redox (APX3330) and repair (compound 3) activities, APE1-deficient or -reconstituted cell lines expressing redox-deficient or endonuclease-deficient proteins, and APX3330-treated mice, we determined the contributions of both endonuclease and redox functions of APE1 in CSR. We found that APE1's endonuclease activity is essential for IgA-class switch recombination. We provide evidence that the redox function of APE1 appears to play a role in regulating CSR through the interleukin-6 signaling pathway and in proper IgA expression. Our results shed light on APE1's redox function in the control of cancer growth through modulation of the IgA CSR process.

Human milk induces IgA class switch recombination in cord blood B-cells

Human milk induces IgA class switch recombination in cord blood B-cells

Mesenteric CD103+DCs Initiate Switched Coxsackievirus B3 VP1-Specific IgA Response to Intranasal Chitosan-DNA Vaccine Through Secreting BAFF/IL-6 and Promoting Th17/Tfh Differentiation.

Intranasal chitosan-formulated DNA vaccination promotes IgA secretion in the intestine. However, the mechanism whereby chitosan-DNA skews IgA class switch recombination (CSR) of B cells in the Gut-associated lymph tissue (GALT) is not fully resolved. In this study, we investigated the effects of nasally administered chitosan-DNA (pcDNA3.1-VP1 plasmid encoding VP1 capsid protein of Coxsackievirus B3) on IgA production, DC activation and Tfh/Th17 response in the intestine. Compared to DNA immunization, intranasal chitosan-DNA vaccination induced antigen-specific IgA production in feces, a pronounced switching of antigen-specific IgA+ plasmablast B cells in the mesenteric lymph nodes (MLNs) and an enhanced expression of post-recombination Iα-CH transcripts/IgA germline transcript (αGT) as well as activation-induced cytidine deaminase (AID) in MLN B cells. MLN Tfh frequency was markedly enhanced by chitosan-DNA, and was associated with VP1-specific IgA titer. 24 h after immunization, intranasal chitosan-DNA induced a recruitment of CD103+DCs into the MLN that paralleled a selective loss of CD103+DCs in the lamina propria (LP). In vivo activated MLN-derived CD103+DCs produced high levels of IL-6 and BAFF in response to chitosan-DNA, which up-regulated transmembrane activator and CAML interactor (TACI) expression on MLN B cells. Upon co-culture with IgM+B in the presence of chitosan-DNA, MLN CD103+DCs induced IgA production in a T-dependent manner; and this IgA-promoting effect of CD103+DC was blocked by targeting TACI and, to a lower extent, by blocking IL-6. MLN CD103+DCs displayed an enhanced capacity to induce an enhanced CD4+Th17 response in vivo and in vitro, and IL-17A deficient mice had a pronounced reduction of specific intestinal IgA following immunization. Taken together, mesenteric CD103+DCs are indispensable for the adjuvant activity of chitosan in enhancing DNA vaccine-specific IgA switching in gut through activating BAFF-TACI and IL-6-IL-6R signaling, and through inducing Th17/Tfh differentiation in the MLN.

Murine γδ T Cells Render B Cells Refractory to Commitment of IgA Isotype Switching.

γδ T cells are abundant in the gut mucosa and play an important role in adaptive immunity as well as innate immunity. Although γδ T cells are supposed to be associated with the enhancement of Ab production, the status of γδ T cells, particularly in the synthesis of IgA isotype, remains unclear. We compared Ig expression in T cell receptor delta chain deficient (TCRδ−/−) mice with wild-type mice. The amount of IgA in fecal pellets was substantially elevated in TCRδ−/− mice. This was paralleled by an increase in surface IgA expression and total IgA production by Peyer's patches (PPs) and mesenteric lymph node (MLN) cells. Likewise, the TCRδ−/− mice produced much higher levels of serum IgA isotype. Here, surface IgA expression and number of IgA secreting cells were also elevated in the culture of spleen and bone marrow (BM) B cells. Germ-line α transcript, an indicator of IgA class switch recombination, higher in PP and MLN B cells from TCRδ−/− mice, while it was not seen in inactivated B cells. Nevertheless, the frequency of IgA+ B cells was much higher in the spleen from TCRδ−/− mice. These results suggest that γδ T cells control the early phase of B cells, in order to prevent unnecessary IgA isotype switching. Furthermore, this regulatory role of γδ T cells had lasting effects on the long-lived IgA-producing plasma cells in the BM.

A single intranasal immunization with a subunit vaccine formulation induces higher mucosal IgA production than live respiratory syncytial virus

Respiratory syncytial virus (RSV) causes serious respiratory illness in infants and elderly. RSV infection induces short-lived immunity, which leaves people prone to re-infection. In contrast, the RSV fusion (F) protein formulated with a novel adjuvant (∆F/TriAdj) elicits long term protective immunity. A comparison of RSV-immunized mice to mice vaccinated with a single dose of ∆F/TriAdj showed no difference in IgG1 and IgG2a production; however, local IgA secreting memory B cell development and B cell IgA production were significantly lower in RSV vaccinated mice than in ∆F/TriAdj-immunized mice. This indicates a potential reason as to why long-term immunity is not induced by RSV infection. The comparison also revealed that germinal center lymphocyte populations were higher in ∆F/TriAdj-vaccinated mice. Furthermore, ∆F/TriAdj induced higher gene expression of activation-induced cytidine deaminase (AID), as well as IL-6, IL-21, TGF-β cytokines, which are key players in IgA class switch recombination, ultimately leading to a sustained long-term memory response.

Regulation of IgA Class Switch Recombination in Immunoglobulin A Nephropathy: Retinoic Acid Signaling and BATF

Background: Immunoglobulin (Ig) A nephropathy (IgAN) is the finding of immune deposits predominantly containing polymeric IgA in the glomerular mesangium on renal biopsy. Increasing evidence suggested that retinoic acid (RA) signaling selectively induces IgA isotype switching and basic leucine zipper transcription factor, ATF-like (BATF) controls the global regulators of class switch recombination (CSR) in lymphocytes. Great effort has been paid to identify whether impaired immune regulation along the ‘mucosa-bone marrow (BM) axis' play an important role in the pathogenesis of IgAN. Methods: The aim of the study was to investigate the expression of all-trans-RA (ATRA) and BATF, and to identify their impact on IgA CSR in IgAN patients and rat animal models. Blood samples and tonsillar tissue specimens were obtained from 22 patients with IgAN and 24 patients with chronic tonsillitis as control. Results: Immunohistochemical, RT-PCR and western blotting examination revealed that RA signaling and BATF productions are activated in IgAN patients compared with controls. Lipopolysaccharide and α-hemolytic streptococcus stimulation upregulated RA receptor (RAR) and BATF expression, promote IgA CSR and ATRA productions in tonsil mononuclear cells. RAR alpha (RARα) or BATF siRNA decreases IgA expression. We also built IgAN rat models and found that RARα, BATF and activation-induced cytidine deaminase were upregulated in the peripheral blood, spleen and BM. With ATRA (500 μg/kg body weight) treatment for 8 weeks, IgA deposition on glomeruli and mesangial cells proliferation increased. It also revealed that ATRA activated BATF and IgA CSR in vivo. Conclusion: These data point toward the role of RA signaling together with BATF in IgA CSR of IgAN, and the data also support the notion that mucosal immunization with neoantigen results in impaired mucosal and systemic IgA responses.

Plasmacytoid dendritic cells are dispensable for noninfectious intestinal IgA responses in vivo.

Intestinal DCs orchestrate gut immune homeostasis by dampening proinflammatory T-cell responses and inducing anti-inflammatory IgA responses. Although no specific DC subset has been strictly assigned so far to govern IgA response, some candidate subsets emerge. In particular, plasmacytoid DCs (pDCs), which notoriously promote anti-viral immunity and T-cell tolerance to innocuous antigens (Ags), contribute to IgA induction in response to intestinal viral infection and promote T-cell-independent IgA responses in vitro. Here, using two transgenic mouse models, we show that neither short-term nor long-term pDC depletion alters IgA class switch recombination in Peyer's patches and frequency of IgA plasma cells in intestinal mucosa at steady state, even in the absence of T-cell help. In addition, pDCs are dispensable for induction of intestinal IgA plasma cells in response to oral immunization with T-cell-dependent or T-cell-independent Ags, and are not required for proliferation and IgA switch of Ag-specific B cells in GALT. These results show that pDCs are dispensable for noninfectious IgA responses, and suggest that various DC subsets may play redundant roles in the control of intestinal IgA responses.

Synthetic Double-Stranded RNA Poly(I:C) Aggravates IgA Nephropathy by Triggering IgA Class Switching Recombination through the TLR3-BAFF Axis

Background: Immunoglobulin class-switch recombination (CSR) is crucial for the expression of IgA, and it plays a vital role in the physiopathology of IgA nephropathy (IgAN). The aim of the study is to investigate the effect of polyriboinosinic:polyribocytidylic acid (poly(I:C)) in modulating toll-like receptor (TLR) 3-B-cell-activating factor belonging to the TNF family (BAFF) axis activation, which in turn promotes IgA CSR of IgAN patients and the IgAN rat model. Methods: Blood samples and tonsillar tissue specimens were obtained from 24 patients with IgAN and 26 patients with chronic tonsillitis as control. We also used the IgAN rat model to investigate the relationship between viral infection and IgA CSR. Results: Immunohistochemical and ELISA western blotting examination revealed that the TLR3/BAFF axis is activated in IgAN patients when compared to controls. Synthetic double-stranded RNA poly(I:C) stimulation upregulates the TACI/TLR3/TRIF/TRAF6 expression and promotes IgA CSR and BAFF productions in tonsil mononuclear cells. TLR3 or BAFF siRNA decreases IgA expression. In IgAN rat models, TLR3/BAFF signaling was highly activated. With 200 μg poly(I:C) sodium salt into the left naris for 8 weeks, IgA was highly deposited on glomeruli. It also revealed that poly(I:C) activated TLR3/BAFF axis and IgA CSR in vivo. Conclusion: These data points toward the role of TLR3/BAFF axis in IgA CSR of IgAN, and the data also support the notion that mucosal immunization with virus infection results in impaired mucosal and systemic IgA responses.

Mo2024 Remifentanil Preconditioning Protects Intestine Against Ischemia/Reperfusion Injury in Rats Through Inhibiting Intestinal Mucosal Epithelial Apoptosis via δ- and μ-Opioid Receptors

Objective: Intestinal ischemia/reperfusion (I/R) frequently occurs after major surgery, various types of shock and severe trauma, and it is associated with a high morbidity and mortality in the critical clinical settings. Intestinal I/R results in the injury of intestinal mucosal immunity and gut bacterial communities, however, little is known about the mechanisms and corresponding therapy for these damages. Immunoglobulin (Ig) A class switch recombination (CSR) plays a major role in gut IgA synthesis, and transforming growth factor (TGF)-β1 can potently induce other Ig isotypes CSR to IgA. Here, we aimed to investigate the effect of TGF-β1 on gut IgA generation and microbiota after intestinal I/R attack, and explore the underlying mechanisms. Methods: The 8-10 weeks Balb/c mice were randomly allocated into 5 groups. In the Sham group, the mice underwent laparotomy without occlusion of the superior mesenteric artery (SMA); whereas, the SMA was clamped for 1 hour in the Injury group; the mice of the TGF group received intravenous infusion of recombinant TGFβ1 before ischemia. In addition, SB-431542, a specific inhibitor of TGF-β receptor I/II, was administered alone (SB group) in intestinal ischemic mice or prior to TGF-β1 (TGF+SB group) to block its inductive effect on IgA CSR. The biomarkers of IgA CSR and IgA mRNA were detected by real-time PCR; the number of IgA+, IgM+ B cells and the percentage of bacteria coated with IgA were detected by flow cytometry; sIgA concentration was detected by ELISA; gut bacterial communities were detected by high-throughput 16S rRNA gene sequencing; and the mortality was analyzed by survival analysis. Results: Intestinal I/R disturbed the process of IgA CSR, and then caused severe disruptions of IgA production and microbiota in the gut. TGF-β1 significantly increased the activation biomarkers of IgA CSR (Fig. 1) and rectified the imbalance of IgA+ and IgM+ B cells in both the peyer's patches and lamina propria, and therefore enhanced gut IgA synthesis and bacteria-binding capacity (Fig. 2A-B). Meanwhile, induction of IgA CSR by TGF-β1 relieved the alterations of gut bacterial richness, diversity and compositions following intestinal I/R (Fig. 2C). Further, the mortality of mice was dramatically reduced. And SB-431542 diminished almost all the protective effects of TGF-β1 on I/R injury. Conclusions: The inhibition of IgA CSR was involved in the pathogenesis of intestinal I/R injury. TGF-β1 improved IgA dysfunction and enteric dysbacteriosis caused by intestinal I/R partly by increasing IgA generation and bacteriabinding capacity via inducing gut IgA CSR.

Mo2023 Induction of Immunoglobulin a Class Switch Recombination by Transforming Growth Factor-β1 Improves Enteric Immunoglobulin a Dysfunction and Dysbacteriosis Following Intestinal Ischemia/Reperfusion in Mice

Objective: Intestinal ischemia/reperfusion (I/R) frequently occurs after major surgery, various types of shock and severe trauma, and it is associated with a high morbidity and mortality in the critical clinical settings. Intestinal I/R results in the injury of intestinal mucosal immunity and gut bacterial communities, however, little is known about the mechanisms and corresponding therapy for these damages. Immunoglobulin (Ig) A class switch recombination (CSR) plays a major role in gut IgA synthesis, and transforming growth factor (TGF)-β1 can potently induce other Ig isotypes CSR to IgA. Here, we aimed to investigate the effect of TGF-β1 on gut IgA generation and microbiota after intestinal I/R attack, and explore the underlying mechanisms. Methods: The 8-10 weeks Balb/c mice were randomly allocated into 5 groups. In the Sham group, the mice underwent laparotomy without occlusion of the superior mesenteric artery (SMA); whereas, the SMA was clamped for 1 hour in the Injury group; the mice of the TGF group received intravenous infusion of recombinant TGFβ1 before ischemia. In addition, SB-431542, a specific inhibitor of TGF-β receptor I/II, was administered alone (SB group) in intestinal ischemic mice or prior to TGF-β1 (TGF+SB group) to block its inductive effect on IgA CSR. The biomarkers of IgA CSR and IgA mRNA were detected by real-time PCR; the number of IgA+, IgM+ B cells and the percentage of bacteria coated with IgA were detected by flow cytometry; sIgA concentration was detected by ELISA; gut bacterial communities were detected by high-throughput 16S rRNA gene sequencing; and the mortality was analyzed by survival analysis. Results: Intestinal I/R disturbed the process of IgA CSR, and then caused severe disruptions of IgA production and microbiota in the gut. TGF-β1 significantly increased the activation biomarkers of IgA CSR (Fig. 1) and rectified the imbalance of IgA+ and IgM+ B cells in both the peyer's patches and lamina propria, and therefore enhanced gut IgA synthesis and bacteria-binding capacity (Fig. 2A-B). Meanwhile, induction of IgA CSR by TGF-β1 relieved the alterations of gut bacterial richness, diversity and compositions following intestinal I/R (Fig. 2C). Further, the mortality of mice was dramatically reduced. And SB-431542 diminished almost all the protective effects of TGF-β1 on I/R injury. Conclusions: The inhibition of IgA CSR was involved in the pathogenesis of intestinal I/R injury. TGF-β1 improved IgA dysfunction and enteric dysbacteriosis caused by intestinal I/R partly by increasing IgA generation and bacteriabinding capacity via inducing gut IgA CSR.

TGF-β and BAFF derived from CD4+CD25+Foxp3+ T cells mediate mouse IgA isotype switching

TGF-β1 is generally accepted as the physiological IgA isotype switch factor. Nevertheless, it is unclear as to which cells in mucus-associated lymphoid tissue provide this cytokine to B cells. Regulatory T cells (Tregs) play immune-suppressive roles by secreting inhibitory cytokines such as TGF-β and IL-10. Thus, it is plausible that Tregs are involved in IgA class switch recombination (CSR) in MALT. We explored, in the present study, the possibility that CD4+CD25+ T cells facilitate IgA CSR in murine B cells. In cocultures, CD4+CD25+Foxp3+ T cells stimulated IgA production by splenic B cells to a greater extent than did CD4+CD25−Foxp3− T cells. This effect was markedly abrogated by the addition of anti-TGF-β1 Ab. Additionally, IgA production was paralleled by an increase in germ line transcript α (GLTα), an indicator of IgA CSR. In contrast, CD4+CD25−Foxp3− T cells were more potent at inducing GLTγ1 and GLTɛ production by cocultured splenic B cells than were CD4+CD25+Foxp3+ T cells. Consistent with these results, phenotypic analyses revealed that TGF-β1 and IL-4 were predominantly expressed by CD4+CD25+Foxp3+ T cells and CD4+CD25−Foxp3− T cells, respectively. Furthermore, CD4+CD25+ T cells strongly expressed BAFF, which led to activation-induced deaminase (AID) expression in B cells. Taken together, our results suggest that CD4+CD25+ Tregs have an important effect on IgA isotype commitment by expressing TGF-β1 and BAFF in MALT.

Oral-Nasopharyngeal Dendritic Cells Mediate T Cell-Independent IgA Class Switching on B-1 B Cells

Native cholera toxin (nCT) as a nasal adjuvant was shown to elicit increased levels of T-independent S-IgA antibody (Ab) responses through IL-5- IL-5 receptor interactions between CD4+ T cells and IgA+ B-1 B cells in murine submandibular glands (SMGs) and nasal passages (NPs). Here, we further investigate whether oral-nasopharyngeal dendritic cells (DCs) play a central role in the induction of B-1 B cell IgA class switch recombination (CSR) for the enhancement of T cell-independent (TI) mucosal S-IgA Ab responses. High expression levels of activation-induced cytidine deaminase, Iα-Cμ circulation transcripts and Iμ-Cα transcripts were seen on B-1 B cells purified from SMGs and NPs of both TCRβ−/− mice and wild-type mice given nasal trinitrophenyl (TNP)-LPS plus nCT, than in the same tissues of mice given nCT or TNP-LPS alone. Further, DCs from SMGs, NPs and NALT of mice given nasal TNP-LPS plus nCT expressed significantly higher levels of a proliferation-inducing ligand (APRIL) than those in mice given TNP-LPS or nCT alone, whereas the B-1 B cells in SMGs and NPs showed elevated levels of transmembrane activator and calcium modulator cyclophilin ligand interactor (TACI) expression. Interestingly, high frequencies of IgA+ B-1 B cells were induced when peritoneal IgA− IgM+ B cells were stimulated with mucosal DCs from mice given nasal TNP-LPS plus nCT. Taken together, these findings show that nasal nCT plays a key role in the enhancement of mucosal DC-mediated TI IgA CSR by B-1 B cells through their interactions with APRIL and TACI.