To determine how cytokine responses are regulated by individual MAP kinases, we pre-treated the cells with ERK1/2 and JNK1/2 inhibitors, respectively, and measured the induction of the cytokines after infection with realtime RT-PCR. We observed that IL-1b was barely detected and not induced during H1N1pdm infection. Interestingly, we noticed that IL-1b was upregulated in the presence of the JNK inhibitor, although no change was observed after the treatment by the ERK inhibitor, indicating that IL-1b could have been induced in swine macrophages infected with H1N1pdm, but was virtually suppressed by JNK1/2 (Fig. 5A) .