C3a (70-77)

C3a (70-77) is an octapeptide corresponding to the COOH terminus of C3a, exhibits the specificity and 1 to 2% biologic activities of C3a. IC50 & Target: Complement system^[1] In Vitro: The direct interaction of C3a(70-77) with human mononuclear leukocytes in culture results in a concentration-dependent inhibition of the generation of LIF evoked by mitogens and by the antigen SK-SD. The extent of suppression of LIF generation by C3a(70-77) is significant at concentrations of 10^-7 M or higher and exceeds 75% at 10^-6 M, irrespective of the stimulus^[1].
C3a (70-77) induces histamine release and degranulation of rat mast cells, promotes contraction of guinea pig ileal tissue, and enhances vascular permeability in human skin. C3a (70-77) selectively desensitizes ileal smooth muscle to C3a but not to human C5a, a related anaphylatoxin. Conversely, C3a-(70-77) is unable to contract ileal smooth muscle pretreated with natural C3a. This cross-desensitization indicates a specific interaction of C3a (70-77) with cellular C3a binding sites^[2].