Comparative study on biological activities of various anaphylatoxins (C4a, C3a, C5a)

Abstract

Several anaphylatoxic substances (human C3a, guinea pig C3a, human C4a, guinea pig C5a, and a synthetic C3a-related hexapeptide) were compared with regard to their ability to induce secretion of [3H] serotonin from guinea pig platelets. Functional identity of the C3a preparations, C4a, and the hexapeptide was demonstrated by the phenomenon of crossed desensitization. Whereas C3a of human and guinea pig origin proved to be qualitatively and quantitatively identical, C4a expressed only 3% of the activity of the C3 fragments on a molar basis. Investigations with goat anti-guinea pig C3a demonstrate that human and guinea pig C3a possess one antigenic determinant in common; however, this determinant is not the C-terminal amino acid sequence. Addition of the anaphylatoxins with low doses of thrombin led to a potentiation of [3H] serotonin release from the platelets. Under these conditions C3a concentrations of 1.5 X 10(-10) mumol/liter (65 pg of C3a) could be detected. Thus the platelet system represents the most sensitive in vitro assay known for evaluation of biological activity of the C3a anaphylatoxins.

Complement activation by both classical and alternative pathways is critical for the effector phase of arthritis

“…Activation of the early components of the classical pathway, C1, C2 and C4, may be sufficient to trigger and maintain a low level of swelling and inflammation in the affected joints. Although C4a is a far less potent anaphylatoxin than C3a and C5a, it induces smooth muscle contraction, an increase in vascular permeability, granule secretion from platelets, and free-oxygen radical generation in macrophages [37][38][39]. Generation of C4a could therefore account for the mild arthritis found in C3 -/-mice.…”

Characterization of Receptors to the Anaphylatoxins on Isolated Cells

“…It has been reported that guinea pig. but not human, platelets have specific receptors to C3a [27] and C5a [28] based on binding and functional studies. When cross-linkage of radiolabeled anaphylatoxins to human and guinea pig platelets was attempted, only the guinea pig platelets had receptors to the anaphylatoxins based on visualization of ligand-receptor bands in SDS-PAGE gels after autoradiography.…”

C4a: An Anaphylatoxin in Name Only

“…Given that C3a and C5a are functional in the nanogram range, this level of contamination (due most likely to the biochemical preparatory methods employed) would be sufficient to induce the reported biological responses. A subsequent study examining the ability of the anaphylatoxins to cross-desensitize guinea pig platelets revealed that C4a had only 3% of the activity of C3a on a molar basis [38]. Given that the C4 used in the study was prepared in exactly the same way as in the study of Gorski et al [34], it is clear that C3a and C5a contamination complicates the interpretation of the reported results.…”