Antiglobulin serum mediated phagocytosis of normal senescent and oxidized RBC: role of anti-IgM immunoglobulins in phagocytic recognition.

Fresh human monocytes usually do not recognize normal RBCs; however, in our newly developed assay antiglobulin-opsonized normal RBCs were phagocytized. Both anti-IgG and anti-IgM fractions present in the antiglobulin serum were involved but the major opsonin was anti-IgM. The anti-IgM opsonized mainly senescent RBCs and therefore could be used to discriminate young from senescent RBCs. The antiglobulin serum and monospecific anti-IgM increased opsonization of in vitro oxidized and desialylated RBCs, whereas trypsin-treatment of RBCs decreased phagocytosis. The material removed by trypsin from the RBCs surface inhibited the antiglobulin and monospecific anti-IgM phagocytic assay supporting the view that membrane associated elements crossreacted with anti-IgM. These results suggest that both internal cellular events and external removal of sialic acid play a role in the emergence of non-IgG covered epitopes on the surface of senescent and oxidized erythrocytes.