TI - NB-1 cells do not express IRF-3 . AB - Among all TLRs , only TLR3 and TLR4 can induce cellular activation in both MyD88 dependent and independent pathway [21] . In the MyD88-independent pathway , LPS treatment leads to activation of transcription factor IRF-3 , followed by production of IFN-beta . Subsequently , IFN-beta activates STAT1 , leading to the induction of several IFN-inducible genes [22-24] . We examined a possibility that NB-1 cells might have a defect in MyD88-independent pathway , especially IRF-3 . Immunoblotting analysis demonstrated that LPS induces PHOSphorylation of IRF-3 in U937 but not in NB-1 cells. (Fig 6A) . Further , we examined the expression of IRF-3 in NB-1 cells and U937 cells . Immunoblotting analysis demonstrated that NB-1 cells did not express IRF-3 (Fig 6B) although it was definitely expressed in U937 cells .