Plays a role in the inhibition of host complement-mediated lysis and serum bactericidal activity by interacting with complement component C5 (PubMed:15728504). Affects all three pathways of complement activation and inhibits the cleavage of C5 by preventing its binding to C5 convertases. In turn, prevents C5a-mediated neutrophil migration (PubMed:20545943). Interacts with host IgA and complement C5; these interactions inhibits complement activation. Belongs to the staphylococcal/streptococcal toxin family.