Role of C3a and C5a in the activation of mast cells.

Mast cells and basophils are known to be triggered by allergens via cross-linking with their high-affinity IgE-binding receptors, Fc epsilon RI. The anaphylatoxic activity of the complement-derived peptides C3a and C5a has been known for a long time; however, it has also been reported that serosal- and mucosal-type mast cells respond differently to peptidergic stimuli. The mechanism of mast cell activation by cross-linking of Fc epsilon RI has been the subject of intensive studies in the past few years, while the action mode of the anaphylatoxic complement peptides has been revealed only recently. We report about a novel function of C3a: its inhibitory activity on IgE-mediated triggering of the mucosal RBL-2H3 cells. Surprisingly, the other anaphylatoxic peptide C5a, which has been shown to be significantly more effective in several biological assays, did not influence antigen-induced triggering of the RBL-2H3 cell line at all.