The NFkB pathway could also be critical in host responses, as has been shown in humans and mice infected with influenza A virus. NFkB can be phosphorylated and activated in swine macrophages in response to H1N1pdm infection ( Fig. 8A and 4C ), albeit at a later stage. Interestingly, when the cells were pre-treated with ERK1/2 or JNK1/2 inhibitors, the phosphorylation of NFkB was also suppressed. However, when the cells were pre-treated with the p38 inhibitor, NFkB phosphorylation decreased much less than with ERK1/2 or JNK1/2 inhibitors (Fig. 8A) . This result suggests that a cross-talk may exist between MAP kinase and NFkB pathways, and that among the MAP kinases, ERK1/2 and JNK1/2 are mainly involved. Figure 5 . Regulation of swine proinflammatory cytokine gene transcripts by MAP kinases. 3D/4 cells were pretreated with U0126 and InSolution JNK inhibitor, which are inhibitors of ERK1/2 and JNK1/2, respectively, 1 hr before H1N1pdm infection. Total RNA was prepared at 24 and 36 hrs post infection for reverse transcription. cDNA was used for realtime PCR with specific primers to measure fold changes of cytokine transcripts at different time points. Each assay was repeated at least twice. A-E. Regulation of IL-1b, IL-6, IL-8, IL-10, and CCL5, respectively, by ERK1/2 and JNK1/ 2 inhibitors. Data show mean fold changes plus standard deviation of two or three independent assays. *p,0.05, Student's t-test. doi:10.1371/journal.pone.0030328.g005