Relative abilities of two Fc gamma receptors on guinea-pig macrophages to operate in the phagocytosis of soluble immune complexes.

Guinea-pig peritoneal macrophages possess two distinct types of Fc gamma receptor (Fc gamma R); one is specific for IgG2 alone (Fc gamma 2R) and the other is specific for both IgG1 and IgG2 (Fc gamma 1/gamma 2R). To study the relative abilities of these Fc gamma Rs to operate in the phagocytosis of soluble immune complexes, the binding, intracellular uptake and subsequent digestion of homologous IgG1 and IgG2 antibodies, complexed with ovalbumin (OA-IgG1 and OA-IgG2), were measured by incubating these complexes with the macrophages, which had been pretreated with the Fab' of monoclonal anti-Fc gamma 2R or anti-Fc gamma 1/gamma 2R antibody. The amount of OA-IgG1 or OA-IgG2 bound to Fc gamma 1/gamma 2R was found to be larger than that of OA-IgG2 to Fc gamma 2R, reflecting that the number of Fc gamma 1/gamma 2R molecules per macrophage is about two times larger than that of Fc gamma 2R molecules. The rates of intracellular uptake and subsequent digestion of Fc gamma 1/gamma 2R bound OA-IgG1 or Fc gamma 1/gamma 2R bound OA-IgG2 were virtually equal to those of Fc gamma 2R bound OA-IgG2, respectively. However, when an excessive amount of OA-IgG2 was incubated with anti-Fc gamma 1/gamma 2R Fab' or anti-Fc gamma 2R Fab' treated macrophages, the phagocytosis mediated by Fc gamma 2R ceased within 4 hr, whereas that mediated by Fc gamma 1/gamma 2R continued up to 6 hr. Thus, the Fc gamma 1/gamma 2R activity seems to be more rapidly restored than the Fc gamma 2R activity in the phagocytosing process.