We propose a novel role for interleukin (IL) 6 in inducing rapid spontaneous proliferation (SP) of naive CD8 + T cells, which is a crucial step in the differentiation of colitogenic CD8 + T cells. Homeostasis of T cells is regulated by two distinct modes of cell proliferation: major histocompatibility complex/antigen -driven rapid SP and IL-7/IL-15 -dependent slow homeostatic proliferation. Using our novel model of CD8 + T cell -dependent colitis, we found that SP of naive CD8 + T cells is essential for inducing pathogenic cytokine-producing effector T cells. The rapid SP was predominantly induced in mesenteric lymph nodes (LNs) but not in peripheral LNs under the infl uence of intestinal fl ora and IL-6. Indeed, this SP was markedly inhibited by treatment with anti -IL-6 receptor monoclonal antibody (IL-6R mAb) or antibiotic-induced fl ora depletion, but not by anti -IL-7R mAb and/or in IL-15 -defi cient conditions. Concomitantly with the inhibition of SP, anti -IL-6R mAb signifi cantly inhibited the induction of CD8 + T cell -dependent autoimmune colitis. Notably, the transfer of naive CD8 + T cells derived from IL-17 ؊ / ؊ mice did not induce autoimmune colitis. Thus, we conclude that IL-6 signaling is crucial for SP under lymphopenic conditions, which subsequently caused severe IL-17 -producing CD8 + T cell -mediated autoimmune colitis. We suggest that anti -IL-6R mAb may become a promising strategy for the therapy of colitis.

The gene region constitutes a high-risk genetic locus for the occurrence of both inflammatory bowel diseases (IBDs) and Parkinson's disease. We show that dendritic cells (DCs) from patients with Crohn's disease (CD) and lymphoblastoid cell lines derived from patients without CD but bearing a high-risk allele (rs11564258) at this locus as heterozygotes exhibited increased LRRK2 expression in vitro. To investigate the immunological consequences of this increased LRRK2 expression, we conducted studies in transgenic mice overexpressing and showed that these mice exhibited more severe colitis induced by dextran sodium sulfate (DSS) than did littermate control animals. This increase in colitis severity was associated with lamina propria DCs that showed increased Dectin-1-induced NF-κB activation and proinflammatory cytokine secretion. Colitis severity was driven by LRRK2 activation of NF-κB pathway components including the TAK1 complex and TRAF6. Next, we found that membrane-associated LRRK2 (in association with TAB2) caused inactivation of Beclin-1 and inhibition of autophagy. HCT116 colon epithelial cells lacking Beclin-1 exhibited increased LRRK2 expression compared to wild-type cells, suggesting that inhibition of autophagy potentially could augment LRRK2 proinflammatory signaling. We then showed that LRRK2 inhibitors decreased Dectin-1-induced TNF-α production by mouse DCs and ameliorated DSS-induced colitis, both in control and transgenic animals. Finally, we demonstrated that LRRK2 inhibitors blocked TNF-α production by cultured DCs from patients with CD. Our findings suggest that normalization of LRRK2 activation could be a therapeutic approach for treating IBD, regardless of whether a risk allele is involved.

It has been reported that IFN-γ-producing CD8(+) T (Tc1) cells express cytotoxic molecules such as perforin and granzyme B to exhibit higher cytotoxicity against tumor cells compared with Tc2 cells. However, the critical role of IL-17-producing CD8(+) T (Tc17)-cell subsets in tumor immunity remains unclear. Tc17 cells differentiated from naive CD8(+) T cells did not possess cytotoxic molecules and exhibited no strong cytotoxicity. However, when Tc17 effector cells were further cultured with IL-12, they converted into IFN-γ-producing Tc17 cells, which mainly consisted of IL-17/IFN-γ double-producing cells (Tc17/IFN-γ). IL-12-converted Tc17 cells also acquired cytotoxic function in addition to IFN-γ producibility. Moreover, they showed strong anti-tumor activity both in vitro and in vivo as well as Tc1 cells. Among four distinct subsets in IL-12-converted Tc17 cell populations, the isolated Tc17/IFN-γ cells exhibited cytotoxicity as well as IFN-γ-producing Tc1-like cells. Thus, we first indicate direct evidence that Tc17/IFN-γ cells, which were plastically converted from non-cytotoxic Tc17 cells by IL-12, exhibited strong anti-tumor activity as well as Tc17 cell-derived Tc1-like cells.

Previous studies have shown that inhibition of receptor-interacting serine/threonine kinase (RICK) (also known as RIP2) results in amelioration of experimental colitis. This role has largely been attributed to nucleotide-binding oligomerization domain 2 (NOD2) signaling since the latter is considered a major inducer of RICK activation. In this study, we explored the molecular mechanisms accounting for RICK-mediated inhibition of inflammatory bowel disease (IBD). In an initial series of studies focused on trinitrobenzene sulfonic acid (TNBS)-colitis and dextran sodium sulfate (DSS)-colitis we showed that down-regulation of intestinal RICK expression in NOD2-intact mice by intra-rectal administration of a plasmid expressing RICK-specific siRNA was accompanied by down-regulation of pro-inflammatory cytokine responses in the colon and protection of the mice from experimental colitis. Somewhat surprisingly, intra-rectal administration of RICK-siRNA also inhibited TNBS-colitis and DSS-colitis in NOD2-deficient and in NOD1/NOD2-double deficient mice. In complementary studies of humans with IBD we found that expression of RICK, cellular inhibitor of apoptosis protein 2 (cIAP2) and downstream signaling partners were markedly increased in inflamed tissue of IBD compared to controls without marked elevations of NOD1 or NOD2 expression. In addition, the increase in RICK expression correlated with disease activity and pro-inflammatory cytokine responses. These studies thus suggest that NOD1- or NOD2-independenent activation of RICK plays a major role in both murine experimental colitis and human IBD.