Macrophage activation selectively enhances expression of Fc receptors for IgG2a

After infection with bacillus Calmette-Guerin, peritoneal macrophages (Mo) display enhanced expression of FcR for both monomeric and complexed IgG2a, but not IgG2b. Isotype specificity of FcR can be reversed on nonactivated Mo by immune lymphokines, and IgG2a immune complexes are more effective triggers of the respiratory burst in activated Mo. Selective enhancement of IgG2a FcR by Mo activation could account for efficacy of homologous ab in mediating cytotoxicity in some systems.