Induction Of IgA Responses Research Articles

IL-17 promotes protective antibody during gut infection through IκB-ζ-dependent LN stromal cell activation

Abstract Fibroblastic reticular cells (FRCs) provide critical regulation of T and B cell. Our recent study shown metabolic reprogramming through Interleukin 17 (IL-17) was critical for the FRCs expansion and autoantibody production. Although studies shown IL-17 is important for B-cell activation and induction of IgA responses, the mechanisms have been unclear. We further hypothesized IL-17 signaling in FRCs is critical to drive protective antibody responses, and prior FRCs activation through a distinct inflammatory episode could enhance this response. We employed Dextran Sulfate Sodium (DSS) induced-colitis followed by Citrobacter rodentium infection model. Mice pretreated with DSS shown increased FRCs expansion and germinal center (GC) formation and enhanced anti-Citrobacter antibody production, leading to a quicker Citrobacter clearance, less colon inflammation and better outcome. IL17a neutralization in DSS phase blocked both the expansion of FRCs and the enhanced B cell response. We further confirmed FRCs failed to expand during Citrobacter infection in FRC-restricted IL-17RA deletion mice. These mice had reduced antibody production in both serum and feces, along with higher Citrobacter burden. We previously shown IL-17 induction IκB-ζ was required for metabolic reprogramming in vitro. Now, we found FRC-intrinsic IκB-ζ expression was required for in vivo Cpt1a (a rate-limiting transporter for fatty acid oxidation) expression, GC formation and antibody responses. RNAseq data suggest GC survival factors such as IL-6 and BAFF were increased by IL-17 signaling in FRCs. In conclusion, IL-17 indirectly promotes GC formation and antibody responses by inducing IκB-ζ expression in activated LN stromal cells during gut infection.

B Cell-Specific Deficiency for Smad2 In Vivo Leads to Defects in TGF-β-Directed IgA Switching and Changes in B Cell Fate

Smad2 is a member of the intracellular mediators that transduce signals from TGF-beta receptors and activin receptors. Targeted inactivation of Smad2 in mice leads to early lethality before gastrulation. It was shown previously that TGF-betaRII deficiency in vivo leads to defects in B cell homeostasis, Ag responsiveness, and IgA class switch recombination of B cells. To investigate the importance of Smad2-mediated signaling in B lymphocytes, we generated a B cell-specific inactivation of Smad2 in mice (bSmad2(-/-)). bSmad2(-/-) mice had normal B cell numbers in the spleen but showed a reduced population of marginal zone B cells. In contrast, B cells in Peyer's patches and peritoneal B-1a cells of bSmad2(-/-) mice were increased in numbers. bSmad2(-/-) mice showed a reduced number of surface-IgA(+) B cells and of IgA-secreting cells in Peyer's patches, decreased levels of IgA in serum, and, after immunization with a T cell-dependent Ag, a reduced IgA response. Class switch recombination to IgA was impaired in Smad2-deficient B cells, when stimulated in vitro with LPS in the presence of TGF-beta. The growth-inhibitory effects of TGF-beta in LPS-stimulated B cells were not affected in Smad2-deficient B cells. In summary, our data indicate a crucial role of Smad2 in mediating signals for the TGF-beta-directed class switch to IgA and the induction of IgA responses in vivo. Other B cell functions like growth-inhibitory signaling, which are known to be regulated by signals via the TGF-betaR, are not affected in Smad2-deficient B cells.

Prenatal Blockage of Lymphotoxin β Receptor and TNF Receptor p55 Signaling Cascade Resulted in the Acceleration of Tissue Genesis for Isolated Lymphoid Follicles in the Large Intestine

Signaling by lymphotoxin (LT) and TNF is essential for the organogenesis of secondary lymphoid tissues in systemic and mucosal compartments. In this study, we demonstrated that the progeny of mice treated with fusion protein of LTbetaR and IgGFc (LTbetaR-Ig) or LTbetaR-Ig plus TNFR55-Ig (double Ig) showed significantly increased numbers of isolated lymphoid follicles (ILF) in the large intestine. Interestingly, double Ig treatment accelerated the maturation of large intestinal ILF. Three-week-old progeny of double Ig-treated mice showed increased numbers of ILF in the large intestine, but not in the small intestine. Furthermore, alteration of intestinal microflora by feeding of antibiotic water did not affect the increased numbers of ILF in the large intestine of double Ig-treated mice. Most interestingly, mice that developed numerous ILF also had increased levels of activation-induced cytidine deaminase expression and numbers of IgA-expressing cells in the lamina propria of the large intestine. Taken together, these results suggest that ILF formation in the large intestine is accelerated by blockage of LTbetaR and TNFR55 signals in utero, and ILF, like colonic patches, might play a role in the induction of IgA response in the large intestine.

TGF-β Receptor Controls B Cell Responsiveness and Induction of IgA In Vivo

To determine the role of the pleiotropic cytokine TGF-β in B cells, we generated mice lacking the TGF-β receptor (TβR) type II selectively in this cell type through conditional mutagenesis (Cre/loxP). The absence of TβRII in B cells leads to a reduced life span of conventional B cells, expansion of peritoneal B-1 cells, B cell hyperplasia in Peyer's patches, elevated serum immunoglobulin, and substantial IgG3 responses to a normally weak immunogen. This B cell hyperresponsiveness is associated with a virtually complete serum IgA deficiency. The data reveal differential roles of TβR in homeostasis and antigen responsiveness of B cell subpopulations and establish a critical function of the TGF-β receptor ligand pair in the induction of IgA responses in vivo.

Lymphocyte subsets in the mammary gland of sows

The presence and localisation of lymphocyte subsets together with class II bearing cells in the mammary gland of sows, were studied at different periods of the reproductive cycle by immunohistochemistry and compared with blood. All cell types involved in the immune response were present in the mammary gland at the different stages of gestation and lactation and nearer the alveolar epithelium as gestation proceeded: T lymphocytes, including CD4+ and CD8+, B lymphocytes and class II bearing cells (epithelial cells and macrophages). The results indicated an early accumulation of T lymphocytes, specifically T helper cells, during pregnancy; the specific increase of IgA lymphocytes occurring after this phase could suggest a role for these T cells in the induction of IgA response. The local accumulation of immune cells sustains the view that the mammary gland is able to mount a true local immune response and the increase in CD8+ cells near the epithelium suggests a role in local immune defence.

Routes of priming and challenge for IgA antibody-containing cell responses in the intestine

The characteristic unresponsiveness of gut-associated lymphoid tissue (GALT) to orally administered antigen has hampered studies of mucosal immunity and the development of effective vaccines to control diseases of mucosal organs. Our previous studies have shown that priming by the intraperitoneal route can overcome this unresponsiveness and enables a vigorous IgA antibody-containing cell (ACC) response from GALT to subsequent intraduodenal (ID) antigen challenge. However the involvement of a concomitant systemic response arising from intraperitoneal priming complicates the analysis of the mucosal component of this response. The studies reported here indicate that immunization of a single Peyer's patch (PP) by subserosal deposition of antigen adjacent to the patch primes for an equivalent IgA ACC response following ID challenge and immunization of multiple PP generates a substantial IgA ACC response in the gut lamina propria even in the absence of luminal challenge. This response persists for at least 84 days. These techniques provide a means by which the requirements for induction of IgA responses can be studied in the absence of a response in systemic lymphoid tissue.

Isotype-specific immunoregulation: T contrasuppressor cells protect IgA responses in oral tolerance.

Murine Peyer’s patches (PP) are enriched in T cell subsets with helper amplifier and contrasuppressor (Tcs) activity (1), and the Tcs cells may play a role in allowing IgA response induction in the presence of T suppressor (Ts) cells which mediate systemic unresponsiveness (1). Continuous oral exposure to thymus-dependent (TD) antigen results in two seemingly-opposite responses, the induction of IgA responses at mucosal sites and systemic unresponsiveness, termed oral tolerance (2,3). C3H/HeJ mice, which are genetically resistant to oral tolerance induction with sheep erythrocytes (SRBC), possess a splenic Tcs cell subset which abolishes oral tolerance when adoptively transferred to syngeneic, C3H/HeN mice. In this study, we summarize recent studies which show that C3H/HeJ PP contain abundant Tcs cell activity which may account for their lack of oral tolerance, and the existence of a Tcs cell subset which preferentially enhances Th cell-mediated IgA responses.