IL-21 ensures TGF-β1-induced IgA isotype expression in mouse Peyer’s patches

Abstract

It is well established that TGF-beta1 induces IgA and IgG2b class-switching recombination in murine B cells. In the present study, we assessed the activity of IL-21 along with TGF-beta1 in Ig synthesis by murine spleen B cells. IL-21 showed antiproliferative activity on LPS-activated splenic B cells, comparable with that of TGF-beta1. IL-21 alone had little effect on IgA secretion and decreased other isotypes. Likewise, IL-21 also did not alter the TGF-beta1-induced IgA synthesis and concurrently diminished the syntheses of IgM and IgG2a, which were repressed by TGF-beta1. Unexpectedly, IL-21 inhibited the TGF-beta1-induced IgG2b production. This IL-21 effect was examined using B cells from IL-21R knockout mice, where the IgA production profile was paralleled by that seen in wild-type B cells. However, the inhibitory effect of IL-21 on TGF-beta1-induced IgG2b synthesis was not seen in the IL-21R(-/-) mouse, suggesting that IL-21 causes TGF-beta1-stimulated B cells to decrease IgG2b synthesis. Expression patterns of Ig germ-line alpha(GL alpha)/GL gamma 2b transcripts under the influence of TGF-beta1 and IL-21 were paralleled by IgA/IgG2b secretion. This was also observed in the activities of GL(alpha) and GL(gamma 2b) promoters. These results indicate that IL-21 decreases IgG2b secretion mainly through inhibition of GL(gamma 2b) transcription and is ultimately associated with selective IgA secretion induced by TGF-beta1. Our results showed that IL-21 was expressed in greater magnitude in Peyer's patches (PP) than in spleen. These results suggest that IL-21 has an important effect on selective IgA(+) B cell commitment in PP.

Decreased PD-1/PD-L1 Expression Is Associated with the Reduction in Mucosal Immunoglobulin A in Mice with Intestinal Ischemia Reperfusion

“…TGF-b1 potently and specifically induces IgA CSR [26], and IL-21, in synergy with TGF-b1, promotes proliferation and differentiation of IgA ? B cells [18]. PP CD4 ?…”

“…Then qRT-PCR was performed on a C1000 Touch Thermal cycler (Bio-Rad laboratories Inc, Hercules, CA) featuring a reaction mixture with SYBR Green as fluorescent dye. The primers for transforming growth factor-b1 (TGF-b1), interleukin-21 (IL-21), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were determined based on previous reports [16,18] (Table 1). The relative amounts of mRNA were calculated by using the standard curve method and normalized by GAPDH.…”

Mucosal B Cell Differentiation and Regulation

“…IL-21 supports plasma cell differentiation in GCs, but recent studies have suggested specific roles in human IgA CSR, including AID induction, activation of Iα promoters, and imprinting of gut homing properties (Avery et al, 2008;Dullaers et al, 2009). Furthermore, in mice, IL-21 inhibits TGF-β-induced activation of GLγ2b transcription, suggesting that it ensures that IgA and not IgG2b is produced at mucosal sites (Seo et al, 2009). …”

“…Whereas the formation of GCs requires CD40 signals in PPs and other secondary lymphoid tissues, T cell subsets distinct from archetypical CD4 + T cells appear to be present in PPs. For example, Seo et al demonstrated that IL-21 was more strongly expressed by CD4 T cells in PPs than in spleen and that, in the context of TGF-β, the dominant isotype produced was IgA, whereas IgG2b antibody production was effectively suppressed by IL-21 (Seo et al, 2009). Whether other aspects than IgA CSR were affected by IL-21 in PPs was not further investigated, but Dullaers and colleagues found that recombinant TGF-β and IL-21 can drive naïve human B cells toward a mucosal phenotype (Dullaers et al, 2009).…”

The Regulation of IgA Production

“…The preferential switching to IgA is partly explained by the fact that bacterial and food-derived products present in gut, such as LPS and retinoic acid, condition PP FDCs, and facilitate the activation of transforming growth factor (TGF)-β1 and secretion of large amounts of B-cell activating factor (BAFF), respectively, two essential cytokines that direct switching toward IgA and survival of recently switched IgA + B cells (Coffman et al, 1989;Mora et al, 2006;Castigli et al, 2005;Cazac and Roes, 2000;McCarthy et al, 2011;Suzuki et al, 2010b). Besides the FDCs, Foxp3 + T cells can convert into T FH cells secreting TGF-β1 and IL-21, and also contribute to the specificity of IgA generation in PP GCs (which will be discussed in the following section) (Avery et al, 2008;Dullaers et al, 2009;Seo et al, 2009). CSR is preceded by expression of germline transcripts initiated from intronic promoters (I), which are located 5′ to the S regions, promoters that are regulated specifically by various cytokines, such as TGF-β1, which induces germline α and γ2b transcripts (Coffman et al, 1989).…”