Murine membrane inhibitor of complement which accelerates decay of human C3 convertase.

A membrane protein of MW 60,000 was purified from mouse erythrocytes. This protein inhibits generation of mouse complement C3/C5 convertases on antibody-sensitized rabbit erythrocytes, in a haemolytic assay system using guinea-pig serum diluted in EDTA as the source of C3 to C9. This protein also has the capacity to accelerate the decay of human C3 convertase of the classical complement pathway. Antibody to this membrane protein also reacted with peripheral blood mononuclear cells and spleen cells, as observed by fluorescent flow cytometry analysis. Since the reactivity of these cells to the antibody was reduced by treatment with phosphatidyl inositol-specific phospholipase C (PIPLC), it is suggested that the protein is attached to the membrane via a glycophospholipid anchor. Based on these results, we conclude that this membrane protein is a murine homologue of human decay-accelerating factor (DAF).