Regulation of phagocytosis and [Ca²⁺]_i flux by distinct regions of an Fc receptor

The binding of multivalent immunoglobulin G complexes to Fc receptors (Fc_γRs) on macrophages activates multiple immune functions. A murine macrophage cell line, but not a fibroblast cell line, that was transfected with human Fc_γRIIA mediated phagocytosis and an intracellular Ca²⁺ concentration ([Ca²⁺]_i) flux upon cross-linking of human Fc_γRIIA. Transfected macrophages that expressed a truncated receptor lacking 17 carboxy-terminal amino acids phagocytosed small antibody complexes. However, only wild-type transfectants phagocytosed labeled erythrocytes and fluxed [Ca²⁺]_i. Thus, the cytoplasmic domain of human Fc_γRIIA contains distinct functional regions.