Contribution of N-acetyl-beta-D-galactosamine-specific lectin to Fc receptor-mediated phagocytosis by mouse peritoneal macrophages.

The contribution of lectin-like receptors on the cell surface of mouse peritoneal macrophages to the process of phagocytosis of IgG-coated sheep red blood cells (SRBC) through Fc receptors has been investigated. Phagocytosis was activated by conditioned medium containing modified vitamin D3-binding protein (DBP) prepared by the incubation of foetal calf serum (FCS) with lysophosphatidyl-choline-treated splenic non-adherent cells. Fc receptor-mediated phagocytosis of opsonized SRBC was specifically inhibited by the addition of N-acetyl-beta-D-galactosamine. The binding of modified Gc globulin, human DBP, to peritoneal macrophage was only inhibited by the addition of N-acetyl-beta-D-galactosamine, and was dependent on N-acetyl-beta-D-galactosamine concentration. In the presence of cycloheximide, activated phagocytosis was reduced to control levels. By Scatchard plot analysis of binding studies, the number of Fc receptors of macrophages which were activated by conditioned medium increased 3.6-fold in comparison to that of control macrophages. These findings suggest that lectin-like receptors having a specificity to N-acetyl-beta-D-galactosamine are involved in activating the process of Fc receptor-mediated phagocytosis of opsonized SRBC by macrophages, and that modified DBP promotes the synthesis of Fc receptors through the N-acetyl-beta-D-galactosamine-specific lectin on macrophage surface.