Complement Component 4a (C4a)

‍‍Anaphylatoxins, or complement peptides, are fragments (C3a, C4a and C5a) that are produced as part of the activation of the complement system. Complement components C3, C4 and C5 are large glycoproteins that have important functions in the immune response and host defense. C3a, C4a and C5a components are referred to as anaphylatoxins: they cause smooth muscle contraction, histamine release from mast cells, and enhanced vascular permeability, and they also mediate chemotaxis, inflammation, and generation of cytotoxic oxygen radicals. C4a is the least active anaphylatoxin.‍‍