Quantifying complement‐mediated phagocytosis by human monocyte‐derived macrophages

The present study demonstrates that SRBC can be opsonized with untreated human serum such that lysis by active complement components is minimal but sufficient opsonization occurs to permit high rates of complement‐mediated phagocytosis. Phagocytosis of SRBC opsonized with 2% whole human serum by human monocyte‐derived macrophages was quantified in a colourimetric assay. Ingestion of SRBC was shown to occur solely via complement receptors because no phagocytosis was observed when SRBC were coated with heat‐ inactivated human serum, phagocytosis was augmented by the phorbol ester, PMA, and phagocytosis was inhibited by a protein kinase C (PKC)‐specific inhibitor RO 31‐8220. This method was used to demonstrate directly that HIV‐1 infection of human monocyte‐derived macrophages inhibits complement‐mediated phagocytosis and will provide a useful tool for pharmacological investigations on complement‐mediated phagocytosis by adherent macrophages.