To quantitate C3 and C5a protein levels during influenza infection, C57BL/6 mice were lightly anesthetized and intranasally inoculated with PBS (uninfected control), seasonal H1N1 A/Puerto Rico/8/1934 (PR/8), pandemic 2009 H1N1 A/California/7/2009 (CA/09), or HPAI H5N1 A/Vietnam/1194/04 (VN/1194) and bronchioalveolar lavage (BAL) collected on days 1, 3, and 6 post-infection (pi). The gene discussed is C3; the disease is influenza.