FH and infection: In addition, human IAV strains have been shown to interact directly with FH (28) and modulate differentially infection of lung epithelial cell line, A549 cells, by IAV strains: this effect of factor H binding to IAV subtypes was assayed in a way that did not activate complement (i.e. in serum-free conditions), suggesting that FH can have a complement-activation independent functions against IAV.