Immunology
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The C5a anaphylatoxin is a potent complement-derived mediator of inflammation with chemotactic activity. In this study the possible role of specific high-affinity binding sites for C5a on peripheral blood leucocytes for the removal of C5a from human blood plasma was investigated. The addition of purified granulocytes or mononuclear cells to complement-activated plasma resulted in the rapid and dose-dependent removal of up to 80% of plasma C5a, as determined by ELISA. ⋯ The inhibition of C5aR internalization by monensin did not affect C5a uptake by leucocytes. The co-incubation with leucocytes had no effect on the plasma clearance of complement activation products C3a or terminal complement complex (TCC), as determined by this in vitro assay. The binding of the C5a anaphylatoxin to cellular receptors represents an effective control mechanism that protects the organism from systemic effects of this potent phlogistic mediator.