Isolation of the phagocytosis-inducing IgG-binding antigen on senescent somatic cells

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Abstract
To remove senescent red blood cells (RBC) from the circulation, macrophages must distinguish them from mature RBC. This is achieved by a specific recognition system. An antigen that develops on the surface of a senescing RBC is recognized and bound by the Fab region of an IgG autoantibody in the serum. Subsequently the Fc region of the autoantibody is recognized and bound by a macrophage, which proceeds to phagocytose the RBC. The antigenic molecule can be extracted from senescent but not young RBC with Triton X-100, although 10-30% as much antigen can be extracted from middle-aged as from senescent RBC. IgG autoantibodies eluted from senescent [human] RBC were used to isolate and purify the IgG-binding antigen on senescent RBC and to detect the antigen on other somatic cells. The antigen is a .simeq. 62,000 MW protein which is present on stored platelets, lymphocytes and neutrophils, and on cultured human adult liver and embryonic kidney cells, as well as senescent RBC.