IgG‐binding sites on macrophage cell membrane. II. Mobility of Fc receptors induced by the interaction with their corresponding IgG ligands

Abstract

Mouse peritoneal macrophages were charged with IgG molecules in monomeric (mIgG), heat-aggregated (agIgG) or antigen-complexed (acIgG) form. Upon exposure to 37 degrees C, all bound IgG ligand types are redistributed on the cell surface due to the mobilization of their corresponding Fc receptor (FcR). The major findings regarding the fate of FcR on macrophages bearing IgG ligands are as follows: (a) the FcR involved in the binding of cytophilic molecules has a slow movement on the cell membrane and forms patches but never caps, while the opsonic type of FcR is rapidly capped; (b) the mobility of IgG-binding sites was temperature-dependent and was affected differently by sodium azide; this metabolic inhibitor enhances the disappearance of mIgG from the cell surface but decreases the capping and the disappearance of polymeric ligands; (c) both FcR types are probably ingested when complexed with specific ligand, and consequently, the rebinding of homologous IgG molecules is reduced, the clearing induced by agIgG or acIgG binding being much more extensive; and (d) cells cleared of their opsonic types of FcR are able to regenerate the receptor molecules with 8 h of incubation at 37 degrees C.

Mechanism of binding of multivalent immune complexes to Fc receptors. 1. Equilibrium binding

“…Finally, it should be emphasized that this quantitative fit does not mean that the model is a unique description of the system. However, the BDPE oligomers are multivalent, and it has been observed that Fc receptors can move in the plane of the plasma membrane (Dickler, 1976;Silverstein et al, 1977;Sulica et al, 1979;Michl et al, 1979). Therefore, the model provides a simple, rational description based on known properties of the system.…”

The Disappearance of SpA‐IgG Antibody Complex on ‘Armed’ Lymphoid and Macrophages Cells

“…The rapid loss of rosetting ability acquired by 'arming' most probably refiects the fast turnover of Fc receptors. In fact, results were obtained showing that rabbit antigencomplexed and human heat-aggregated IgG molecules very rapidly induced modulation of Fc receptors on mouse macrophages incubated at 37°C, and that the endocytosis ofthe IgG-Fc receptor complex accounts for the rapid disappearance of polymer molecules from the cell membrane [12]. Similar modulation of Fc receptors may also be involved in the loss of SpA complexes from the lymphoid surface, as was actually found in the case of aggregated IgG ligand [11].…”