Induction of thromboxane release from macrophages by anaphylatoxic peptide C3a of complement and synthetic hexapeptide C3a 72-77.

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Abstract
Guinea pig peritoneal macrophages were examined for their response to homologous anaphylatoxic peptide C3a of complement. C3a caused the release of considerable amounts of thromboxane A2 from macrophages maintained in serum-free culture for up to 12 hr. Preincubation of C3a with the Fab portion of a monoclonal anti-C3a IgG abrogated its stimulatory capacity. C3a desarg was found to be rather ineffective in eliciting thromboxane release. Hexapeptide C3a 72-77, comprising the C-terminal amino acids of human C3a, proved also to stimulate the cyclooxygenation pathway of macrophage arachidonic acid metabolism, following the same routes of receptor-ligand interactions (rapid onset of activation, low dose, and cumulative desensitization) as proven for other anaphylatoxin-cell interactions. This novel effect of anaphylatoxins C3a and C3a 72-77 could contribute to inflammatory reactions in which macrophages play a role.