All classes of murine IgG antibody mediate macrophage phagocytosis and lysis of erythrocytes.

Antibody-dependent phagocytosis and lysis of sheep RBC by mouse peritoneal exudate cells were studied using IgG subclass fractions of sera prepared by protein A-Sepharose chromatography. Three IgG1, 3 IgG2a, 4 IgG2b, and 1 IgG3 hybridoma antibodies to RBC were also used. The results showed that some monoclonal IgG2a and IgG2b antibodies were more active than IgG1 or IgG3 preparations when normalized to hemagglutinating activity, but all IgG sources mediated both effector mechanisms. This is in accord with findings of strong Fc receptors on macrophages for the IgG2 isotypes and weaker binding by IgG1 and newly discovered IgG3 receptors. A monoclonal IgG2b with no hemagglutination titer showed normal cooperation with macrophages. In contrast, 2 hybridoma IgM were inactive in macrophage-mediated lysis and allowed only marginal ingestion. Similar results were obtained using several macrophage cell lines, mouse spleen and human peripheral blood mononuclear cells, showing that all these types of effector cells do not distinguish among (mouse) IgG subclasses in handling antibody-coated RBC.