Contribution of mannose receptor to signal transduction in Fc gamma receptor-mediated phagocytosis of mouse peritoneal macrophages induced by liposomes.

The contribution of mannose receptors on the cell surface of mouse peritoneal macrophages to the process of liposome-induced phagocytosis of immunoglobulin G-opsonized sheep red blood cells (SRBCs) through Fc gamma receptor has been investigated. Fc gamma receptor-mediated phagocytosis of opsonized SRBCs was activated by modified alpha 2-macroglobulin, which was produced in the incubation mixture of alpha 2-macroglobulin and liposome-treated splenic B cells. The phagocytosis was specifically inhibited by the addition of D-mannose, and the inhibition was dependent on the D-mannose concentration. The binding of modified alpha 2-macroglobulin to macrophages was also reduced by the addition of D-mannose. The activation effect of modified alpha 2-macroglobulin was not inhibited when in the presence of alpha 2-macroglobulin-trypsin and -methylamine complexes. In the presence of cycloheximide, activated phagocytosis was reduced to the control level. By Scatchard plot analysis of IgG binding studies, the number of Fc gamma receptors of a macrophage had been increased to 4.6-fold that of a control macrophage by treatment with modified alpha 2-macroglobulin. These findings suggest that macrophage mannose receptors are involved in activating the process of Fc gamma receptor-mediated phagocytosis of opsonized SRBCs induced by modified alpha 2-macroglobulin. Lectins may participate in a signal transduction in macrophage activation by liposomes.