TLR4 and influenza: To further evaluate the role of distinct strain backgrounds and the role of TLR4 in influenza-induced lethality, wild-type C3H/HeOuJ and C3H/HeJ mice, the latter strain shown to express a point mutation in the TIR domain of TLR4 that resulted in a loss of TLR4-mediated signaling (140, 141), were challenged with mouse-adapted influenza H1N1 PR8.