Redistribution of the Fc receptor on human blood monocytes and peritoneal macrophages induced by immunoglobulin G-sensitized erythrocytes.

The Fc receptor is a plasma membrane component exhibiting an affinity for the C gamma 3 domain of certain subclasses of immunoglobulin G. Using anti-Rho (D)-sensitized red cells (EA) in a slide rosette technique, we have demonstrated a translational mobility and polar redistribution of this receptor on the human blood monocyte and peritoneal macrophage. These cells, isolated from venous blood and malignant ascites and identified histochemically, showed a time- and temperature-dependent receptor capping defined by binding six or more EA confined to the cell half-perimeter. Caps formed in serum were mainly extreme caps in which bound EA appeared as a morula contiguous with the adherent cell. At 21 degrees C and 37 degrees C in serum 80% live rosettes formed caps; virtually none formed at 4 degrees C and about 25% were seen in PBS at 21 degrees C. Similarly, 10% extreme caps in PBS and 60 and 70% in serum were seen at room temperature and 37 degrees C, respectively, suggesting a serum factor(s) was important in promoting live rosette capping. Capping was reversibly inhibited by sodium azide although inhibition was incomplete even at 0.1 M, a concentration 10-fold higher than that giving complete inhibition of lymphocyte antigen-receptor capping. Azide also induced reversion of capped rosettes to diffuse, noncapped rosettes, and to levels comparable to those seen in inhibition studies. Re-exposure to EA after rosette capping failed to increase either the proportion of cells forming rosettes or the fullness of such rosettes indicating a critical number of receptors had been capped. Live rosettes induced a spherocytosis in bound EA irrespective of capping status; such changes appeared early in PBS where capping was minimal. Dead cells bore EA as normal biconcave discs. Some rosetting EA were ultimately hemolyzed upon prolonged incubation, and erythrophagocytosis was seen in about 15% of capped rosettes at 37 degrees C.