Rabbit antibodies were prepared against purified mouse macrophages, erythrocytes, and liver lysosomes. In the presence of complement each of these reagents was capable of lysing mouse erythrocytes and macrophages. In the absence of complement, all antisera agglutinated mouse erythrocytes and at high concentration produced a cytotoxic effect on macrophages. At IgG concentrations of 100 µg/ml, no morphological evidence of cytotoxicity was evident. These data suggest the presence of common antigens on the erythrocyte and macrophage plasma membrane.

Anti-macrophage, anti-erythrocyte, and anti-lysosomal γ-globulins and IgG, employed at subtoxic concentrations, all inhibited the attachment and ingestion of opsonized erythrocytes and mycoplasma. This occurred without significant reduction in the phagocytosis of polystyrene particles, formalinized erythrocytes, and yeast cell walls. Each of the anti-membrane IgG antibodies was capable of blocking the Fc receptor on the macrophage plasma membrane. Attachment to the macrophage membrane occurred by means of the Fab region. However, a role for the Fc portion of the molecule was suggested since pepsin-digested IgG was unable to block the receptor.

Each of the IgG antibodies produced a partial blockade of the complement receptor and reduced the ingestion of EAC1,4,2,3 by approximately 50%.

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