Complement and Allergy

Anaphylatoxin was originally described as a toxin produced in the blood after incubation with immune precipitates. This toxin caused adverse symptoms resembling severe systemic anaphylaxis and allergy when injected into animals. As the biochemistry of the complement system was revealed, anaphylatoxin activity was found to originate from the complement components C3 and C5. These initial observations formed the basis for the longstanding idea that the complement system is important in allergy. The anaphylatoxins C3a and C5a are approximately 10 kD fragments of the amino terminus of the alpha chain of C3 and C5, respectively. C4a is also an anaphylatoxin, but is less potent than C3a and C5a, and its relevance in vivo is less clear. When injected into animals, C3a and C5a cause symptoms resembling immune-mediated hypersensitivity. This provides the rationale for investigations of the complement system in allergy and hypersensitivity. Increasing information on the biochemistry….