Endocytosis by Macrophages of Altered Soluble Protein. The Effect of Binding to Particulate Surfaces and of IgM and IgM Antibody

Abstract

Keyhole limpet hemocyanin (KLH) was bound to homologous rat erythrocytes with CrCl₃ or to Bio-Gel beads with carbodiimide. When bound KLH was offered to rat peritoneal exudate cells, in vitro, uptake was 18 to 70 times greater than uptake of free unbound KLH. The augmented uptake was the result of enhanced endocytosis without phagocytosis of the binding particles. Protein in medium containing suspensions of macrophages depressed uptake of bound and free KLH, but depressed the latter significantly more. Endocytosis of bound KLH was not affected by γ-globulin, antibodies to rat IgG, or antibodies specific for and bound to rat macrophages, beyond the depressing effect of protein. IgM antibody to KLH was significantly more effective in increasing uptake of free KLH than was IgG antibody to KLH, whereas both antibodies to KLH had little effect on uptake of bound KLH. The enhanced uptake of bound KLH was probably due to the form and manner in which the protein was offered to macrophages.