A novel signal transducer TAB2 which acts as an adapter molecule of TRAF6 and TAK1 and mediates the activation of TAK1 in the signal transduction of IL-1 was isolated. TAB2 induced the activation of NF-.kappa.B and JNK by IL-1. The signal transduction by IL-1 was inhibited by inhibiting the signal transduction of TAB2 with the use of a dominant negative mutant of TAB2. A compound inhibiting the signal transduction in TAB2 is useful as an anti-inflammatory drug.