Targeted Disruption of the MyD88 Gene Results in Loss of IL-1- and IL-18-Mediated Function

MyD88, originally isolated as a myeloid differentiation primary response gene, is shown to act as an adaptor in interleukin-1 (IL-1) signaling by interacting with both the IL-1 receptor complex and IL-1 receptor–associated kinase (IRAK). Mice generated by gene targeting to lack MyD88 have defects in T cell proliferation as well as induction of acute phase proteins and cytokines in response to IL-1. Increases in interferon-γ production and natural killer cell activity in response to IL-18 are abrogated. In vivo Th1 response is also impaired. Furthermore, IL-18-induced activation of NF-κB and c-Jun N-terminal kinase (JNK) is blocked in MyD88−/− Th1-developing cells. Taken together, these results demonstrate that MyD88 is a critical component in the signaling cascade that is mediated by IL-1 receptor as well as IL-18 receptor.