Specificity of Fc-Receptors on Lymphocytes and Monocytes for Guinea-Pig IgG1 and IgG2: Induction and Inhibition of Cytolysis or Phagocytosis of Erythrocytes

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Abstract
The capacity of guinea-pig Ig[immunoglobulin]G1 and IgG2 antibodies to induce lymphocyte (K[antibody-dependent cytotoxic]-cell) mediated lysis or monocyte/macrophage mediated phagocytosis of erythrocytes was studied with human and guinea-pig effector cells. For both species, induction of K-cell mediated lysis was restricted to IgG2. IgG1 and IgG2 could induce monocyte/macrophage mediated phagocytosis. In competitive inhibition experiments, only complexed IgG2 inhibited lysis mediated by K-cells. The Fc-receptors on K-cells probably only recognize IgG2. Complexes of both subclasses inhibited phagocytosis by human monocytes, regardless of the subclass of the inducing antibodies. Inhibition of guinea-pig macrophage mediated phagocytosis by IgG2 complexes was also independent of the inducing antibody. Hence, Fc-receptors common for IgG1 and IgG2 seem to be involved in the monocyte/macrophage mediated effector reaction. Free IgG1 was significantly less inhibitory than free IgG2 for human monocytes and hardly at all for guinea-pig macrophages. However, free IgG2, which was cytophilic for these cells, was more aggregated than IgG1. Thus, both molecular structure and state of aggregation determine interaction of IgG with cellular Fc-receptors.