These clinical signs are the result of a cascade of events: complement activation leads to release of anaphylatoxins (primarily C3a and C5a) which activate blood cells and other allergy-mediator secretory cells to release vasoactive inflammatory mediators which then cause autonomic responses such as capillary leakage, bronchoconstriction, vasoconstriction, and vasodilation. Here, C3 is linked to Allergy.