IL-4 exacerbates disease in a Th1 cell transfer model of colitis

IL-4 is associated with Th2-type immune responses and can either inhibit or, in some cases, promote Th1-type responses. We tested the effect of IL-4 treatment on the development of inflammation in the CD4⁺CD45RB^high T cell transfer model of colitis, which has been characterized as a Th1-dependent disease. IL-4 treatment significantly accelerated the development of colitis in immunodeficient recipients (recombinase-activating gene-2 (Rag2)^-/-) of CD4⁺CD45RB^high T cells. Quantitative analysis of mRNA expression in the colons of IL-4-treated mice showed an up-regulation of both Th1- and Th2-associated molecules, including IFN-γ, IP-10, MIG, CXCR3, chemokine receptor-8, and IL-4. However, cotreatment with either IL-10 or anti-IL-12 mAb effectively blocked the development of colitis in the presence of exogenous IL-4. These data indicate that IL-4 treatment exacerbates a Th1-mediated disease rather than induces Th2-mediated inflammation. As other cell types besides T cells express the receptor for IL-4, the proinflammatory effects of IL-4 on host cells in Rag2^-/- recipients were assessed. IL-4 treatment was able to moderately exacerbate colitis in Rag2^-/- mice that were reconstituted with IL-4Rα-deficient (IL-4Rα^-/-) CD4⁺CD45RB^high T cells, suggesting that the IL-4 has proinflammatory effects on both non-T and T cells in this model. IL-4 did not cause colitis in Rags2^-/- mice in the absence of T cells, but did induce an increase in MHC class II expression in the lamina propria of the colon, which was blocked by cotreatment with IL-10. Together these results indicate that IL-4 can indirectly promote Th1-type inflammation in the CD4⁺CD45RB^high T cell transfer model of colitis.