In vivo administration of IL-18 can induce IgE production through Th2 cytokine induction and up-regulation of CD40 ligand (CD154) expression on CD4+ T cells

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Abstract
IL‐18 is considered to be a strong cofactor for CD4+ T helper 1 (Th1) cell induction. We have recently reported that IL‐18 can induce IL‐13 production in both NK cells and T cells in synergy with IL‐2 but not IL‐12, suggesting IL‐18 can induce Th1 and Th2 cytokines when accompanied by the appropriate first signals for T cells. We have now found that IL‐18 can act as a cofactor to induce IL‐4, IL‐10 and IL‐13 as well as IFN‐γ production in T cells in the presence of anti‐CD3 monoclonal antibodies (mAb). IL‐18 can rapidly induce CD40 ligand (CD154) mRNA and surface expression on CD4+ but not CD8+ T cells. The administration of IL‐18 alone in vivo significantly increased serum IgE levels in C57BL/6 (B6) and B6 IL‐4 knockout mice. Furthermore, the administration of IL‐18 plus IL‐2 induced approximately 70‐fold and 10‐fold higher serum levels of IgE and IgG1 than seen in control B6 mice, respectively. IgE and IgG1 induction in B6 mice by administration of IL‐18 plus IL‐2 was eliminated by the pretreatment of mice with anti‐CD4 or anti‐CD154, but not anti‐CD8 or anti‐NK1.1 mAb. These results suggest that IL‐18 can induce Th2 cytokines and CD154 expression, and can contribute to CD4+ T cell‐dependent, IL‐4‐independent IgE production.

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