Specific antibody-dependent phagocytosis of lipid vesicles by RAW264 macrophages results in the loss of cell surface Fc but not C3b receptor activity.

Abstract

We have observed that the specific antibody-dependent phagocytosis of lipid vesicles (containing 1 to 2% phospholipid hapten) results in a loss of Fc surface receptor activity from RAW264 macrophages. The Fc-receptor activity was measured by the ability of the macrophages to form rosettes with antibody-coated sheep erythrocytes (E). C3b-receptor activity was monitored similarly by measuring rosetting of IgM and complement-coated sheep erythrocytes (EAC). Under the same conditions, there was no loss of C3b-receptor activity. This suggests that Fc but not C3b cell surface receptors are depleted during specific IgG-mediated phagocytosis. The rosette assay for receptors, in accord with a previous kinetic analysis of vesicle uptake, showed that the depletion of Fc receptors after phagocytosis of specific antibody-coated vesicles was highly dependent on the number of vesicles taken up but relatively independent of the density of IgG bound to the vesicle surface. In contrast to the above results the nonspecific phagocytosis of latex beads results in the loss of both Fc- and C3b-receptor activity as measured by rosetting experiments.