TLR4 and pneumonia: Although TLR signaling pathways play an important role in innate immunity to virus infection, activations of TLR3, TLR4, and TLR7 signaling pathways have been reported to be required for IAV proliferation, and lasting activation of TLR pathways can even support IAV replication and is detrimental to IAV-induced acute pneumonia [11,12,13,15,16].