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In the intestine, immune responses to commensal microbes should be regulated precisely. This regulation is achieved partly by dendritic cells (DCs), which recognize microbes through Toll-like receptors (TLRs). Although TLR responses have been intensely studied, cross-talk between individual TLRs remains unclear. The present study shows that TLR2 suppressed TLR9-induced Il12b gene expression and subsequent interleukin (IL)-12 and IL-23 production in DCs from Peyer's patch, a lymphoid tissue in the small intestine. The DCs expressed Il12b gene and produced IL-12 and IL-23 in response to TLR9 stimulation, and these responses were suppressed when the DCs were stimulated simultaneously with TLR2. The suppression was also observed in the non-intestinal DCs, such as spleen DCs and bone marrow-derived DCs. Peyer's patch DCs expressed Il12b gene also in response to TLR7 or CD40 stimulation, but these responses were not suppressed by simultaneous TLR2 stimulation. In addition, TLR9-induced Tnf and Il6 gene expression was not suppressed by TLR2. Furthermore, the supernatant of TLR2-stimulated DCs could not suppress TLR9-induced Il12b gene expression. These results suggest that TLR2 suppress TLR9-induced responses selectively, and this suppression is not mediated by secretory factors. The suppressive TLR cross-talk might play a certain role in preventing excess inflammatory responses to commensal microbes in the intestine and may have implications for the therapeutic strategies for intestinal inflammatory diseases, autoimmune diseases and cancer., (Copyright © 2015 Elsevier GmbH. All rights reserved.)

It has been demonstrated that intestinal commensal bacteria induce immunoglobulin (Ig) A production by promoting the development of gut-associated lymphoid tissues in the small intestine. However, the precise mechanism whereby these bacteria modulate IgA production in the large intestine, which harbors the majority of intestinal commensals, is poorly understood. In addition, it is not known which commensal bacteria induce IgA production in the small intestine and which induce production in the large intestine. To address these issues, we generated gnotobiotic mice mono-associated with different murine commensal bacteria by inoculating germ-free (GF) mice with Lactobacillus johnsonii or Bacteroides acidifaciens. In GF mice, IgA production was barely detectable in the small intestine and was not detected in the large intestine. Interestingly, total IgA secretion in the large intestinal mucosa of B. acidifaciens mono-associated (BA) mice was significantly greater than that of GF and L. johnsonii mono-associated (LJ) mice. However, there was no difference in total IgA production in the small intestine of GF, LJ and BA mice. In addition, in the large intestine of BA mice, the expression of IgA(+) cells and germinal center formation were more remarkable than in GF and LJ mice. Furthermore, B. acidifaciens-specific IgA was detected in the large intestine of BA mice. These results suggest that the production of IgA in the large intestine may be modulated by a different mechanism than that in the small intestine, and that B. acidifaciens is one of the predominant bacteria responsible for promoting IgA production in the large intestine., (Copyright © 2012 Elsevier GmbH. All rights reserved.)

Bifidobacterium is a dominant bacterial species among commensals in the human intestine and is thought to have probiotic immunomodulatory effects. In this study, we investigated the effect of the association with Bifidobacterium pseudocatenulatum JCM 7041 (Bp) on dietary ovalbumin (OVA)-specific immune responses using germ-free OVA-specific T cell receptor transgenic mice (OVA23-3 mice). We established germ-free OVA23-3 mice, and then associated with Bp (BIF group) or without (CONT group) and additionally associated with segmented filamentous bacteria (SFB) and clostridia in both groups. BIF and CONT mice were fed an egg-white diet containing OVA for 1 week. Cytokine production in response to OVA by cells of Peyer's patches (PPs) and lamina propria (LP) from the small and large intestine was measured. Interferon (IFN)-gamma and interleukin (IL)-6 production by PP cells from BIF group mice was lower than that of the CONT group. The proportion of PP cells expressing CD4+CD62L(low), an activated/memory T cell phenotype, was higher in BIF group mice than the CONT group. Furthermore, LP cells from the small intestine in Bp-associated mice showed a tendency to produce slightly lower IFN-gamma and IL-6, while the cells from large intestine produced markedly higher IFN-gamma, IL-5 and IL-6 than those in the CONT group. The pattern of cytokine production by PP in BIF animals was similar to those isolated from conventional mice. These results suggest that intestinal association with Bp might down-regulate excessive immune responses to dietary antigens of the small intestine but enhance those of the large intestine.

Beneficial effects of lactobacilli have been reported for patients with allergic diseases and intestinal disorders such as inflammatory bowel disease. However, it is not fully understood how such bacteria influence the immunologic response. For this purpose, we investigated the effect of Lactobacillus acidophilus strain L-92 (L-92) on antigen-stimulated T cell responses in vitro and in vivo. In vitro, L-92 decreased the proliferation of CD4(+) T cells stimulated with antigen, and also induced apoptosis of antigen-stimulated T cells. On the other hand, interferon (IFN)-gamma secretion from naïve T cells was increased while interleukin (IL)-4 secretion was decreased by L-92. Co-culture with L-92 induced apoptosis of differentiated Th1 and Th2 cells. The degree of apoptosis induction was higher in Th2 cells. Moreover, L-92 up-regulated the expression of B7-H1 and down-regulated that of B7-H2 on dendritic cells (DCs), and DCs exposed to L-92 also induced apoptosis of antigen-stimulated T cells. Finally, orally administered L-92 induced apoptosis of OVA-specific TCR Tg T cells. These results indicate that L-92 attenuates the CD4(+) T cell response by inducing DC-mediated apoptosis and that it might exert beneficial effects in patients with diseases resulting from a hyper-response of CD4(+) T cells.

Intraepithelial lymphocytes (IELs) are considered to drive immune surveillance of the epithelial layer to the mucosa, which is initially exposed to exogenous antigens. However, how IELs are activated by orally administered antigens remains unclear. To clarify this mechanism, we fed ovalbumin (OVA) to T cell receptor transgenic (TCR-Tg) mice with OVA-specific MHC class II-restricted TCR and found that the cytotoxic activity of IELs was increased against both NK and LAK target cells, but notably reduced after depleting CD8 + IELs. Cytoplasmic staining showed that the production of IFN-gamma and IL-2 was increased in mice fed with OVA both in the supernatant of cultured IELs with immobilized anti-CD3 mAb and in fresh CD4+ IELs. In contrast, the cytotoxic activity against NK and LAK target cells and the production of IL-2 and IFN-gamma was decreased in splenic T cells from mice fed with OVA. However, when the splenic T cells from these mice were cultured with OVA and IL-2, IFN-gamma production recovered. The decreased response demonstrated the clonal anergy of T cells. Furthermore, tumor growth was enhanced in TCR-Tg mice carrying an OVA-transfected counterpart A20 B cell lymphoma (OVA-A20) and fed with OVA. These results indicate that the oral administration of soluble antigens can activate CD4+ IELs in an antigen-specific manner but induces hyporesponsiveness in the spleen. In addition, Th1-type cytokines produced by activated CD4+ IEL might provide a bystander effect on the cytotoxic activity of IELs.