The transcription factor IFN regulatory factor-4 controls experimental colitis in mice via T cell-derived IL-6.

The proinflammatory cytokine IL-6 seems to have an important role in the intestinal inflammation that characterizes inflammatory bowel diseases (IBDs) such as Crohn disease and ulcerative colitis. However, little is known about the molecular mechanisms regulating IL-6 production in IBD. Here, we assessed the role of the transcriptional regulator IFN regulatory factor-4 (IRF4) in this process. Patients with either Crohn disease or ulcerative colitis exhibited increased IRF4 expression in lamina propria CD3+ T cells as compared with control patients. Consistent with IRF4 having a regulatory function in T cells, in a mouse model of IBD whereby colitis is induced in RAG-deficient mice by transplantation with CD4+CD45RB(hi) T cells, adoptive transfer of wild-type but not IRF4-deficient T cells resulted in severe colitis. Furthermore, IRF4-deficient mice were protected from T cell-dependent chronic intestinal inflammation in trinitrobenzene sulfonic acid- and oxazolone-induced colitis. In addition, IRF4-deficient mice with induced colitis had reduced mucosal IL-6 production, and IRF4 was required for IL-6 production by mucosal CD90+ T cells, which it protected from apoptosis. Finally, the protective effect of IRF4 deficiency could be abrogated by systemic administration of either recombinant IL-6 or a combination of soluble IL-6 receptor (sIL-6R) plus IL-6 (hyper-IL-6). Taken together, our data identify IRF4 as a key regulator of mucosal IL-6 production in T cell-dependent experimental colitis and suggest that IRF4 might provide a therapeutic target for IBDs.

IRF4 selectively controls cytokine gene expression in chronic intestinal inflammation.

The authors previously showed that interferon regulatory factor (IRF)4 knockout mice are protected from experimental oxazolone and TNBS colitis. Here the effect of IRF4 on the expression of pro- and anti-inflammatory cytokines in TNBS colitis and long-term CD45RB(high) transfer colitis is examined. In TNBS colitis, no differences were found in interleukin (IL)-18 and tumor necrosis factor (TNF)-alpha expression between IRF4 knockout and wild-type mice. However, significant differences were detected in IL-6 and IL-17 production. Upon treatment with hyper-IL-6, IRF4(-/-) mice lost their protective properties towards TNBS application. Hyper-IL-6 application induced IL-6 mRNA, but not IL-17 mRNA expression, suggesting that IL-6 deficiency is not primarily responsible for the lack of IL-17 production. T-bet and GATA-3 mRNA expressions were not affected upon IL-6 application. In transfer colitis, colonic cytokine mRNA analysis revealed a reduced production of IL-6 in IRF4(-/-) reconstituted mice in the long-term course. In contrast, several other cytokines did not differ between the two groups (e.g. TNF-alpha and IL-10). Measurement of supernatants from splenic mononuclear cells revealed a significant difference in IL-6 and IL-17 production between the two groups. These findings suggest that IRF4 selectively regulates cytokine gene expression in chronic inflammation. IRF4 therefore emerges as an attractive target for the therapy of chronic intestinal inflammation. Blocking IRF4 might be an interesting option to modulate inflammation in the advanced state of inflammation.