Activation of both NF-κB and MAPK can occur in the presence of MyD88. NF-κB p65 was detected using nuclear protein extracts from AMΦ to determine whether LPS-TLR4 up-regulation of TLR3 was the result of activation of NF-κB. As shown in Fig. 3A, in response to LPS in WT mice, the expression of NF-κB p65 increased at 2.5 h and reached a significant level at 4.5 h. However, in TLR4−/− mice, LPS failed to induce nuclear NF-κB p65 expression.