GAPDH and infection: To determine whether IAV infection activates the TrkA signaling, we infected human airway epithelial cells A549 with A/WSN strain at the multiplicity of infection (MOI) of 10 and prepared cell lysates from 0 to 120 min post-infection for Western blotting with antibodies against total TrkA, phosphorylated TrkA (pTrkA), or GAPDH.