Pathogenesis determinants include the intrinsic properties of IAV strains, and their interplay with host defence mechanisms. The Amorim lab found a specific interaction between influenza A virus and the complement system. With renewed interest caused by implementation of successful complement-targeting therapies, the complement is not just a pathogen killer, but a key player in immunity. It bridges innate and adaptive responses, and orchestrates the intensity of immunological and inflammatory processes by communicating with immune cells. Interactions are beginning to be fully appreciated, and their identification is crucial, as excess complement activation is associated with severe outcomes in many infections. Our goal is to understand the mechanisms by which the virus modulates the function of the complement, contributing to better define how complement communicates with other biological systems.