A growing body of evidence has demonstrated complement overactivation in sepsis (44), viral hepatitis (45), human infections with highly pathogenic avian influenza viruses H5N1/H7N9 (46, 47), and C5a inhibitor or C5aR1 knockout is effective in alleviating symptoms of these diseases and reducing infection-induced lethality in vivo. This evidence concerns the gene C5AR1 and Sepsis.