Receptor for the Fc region of complexed immunoglobulins gamma. Low affinity receptor. Involved in a variety of effector and regulatory functions such as phagocytosis of antigen-antibody complexes from the circulation and modulation of antibody production by B-cells. Isoform IIB1 and isoform IIB1' form caps but fail to mediate endocytosis or phagocytosis. Isoform IIB2 can mediate the endocytosis of soluble immune complexes via clathrin-coated pits. Isoform IIB1 and isoform IIB2 can down-regulate B-cell, T-cell, and mast cell activation when coaggregated to B-cell receptors for AG (BCR), T-cell receptors for AG (TCR), and Fc receptors, respectively.