Ganglioside receptor of rat macrophages. Modulation by enzyme treatment and evidence for its protein nature.

Previous experiments have shown that rat macrophages (M phi) bind specifically sheep erythrocytes (E) coated with various gangliosides (EG). To study the nature of this receptor-like structure, M phi were treated with proteinases, and their capacity to bind EG and/or E was analyzed in a rosette assay. Within 10 min of incubation with appropriate doses of enzymes, a clear enhancement of EG-binding activity was observed. In addition, enzyme-treated M phi bound uncoated E. Inhibition studies with gangliosides and carbohydrates, and enzyme treatment of E showed that this binding is mediated by the same M phi ganglioside receptor. The kinetics of the modulation of binding activity of M phi during trypsin treatment were similar for both E and EG. At optimal enzyme concentration a triphasic effect was noted. Enhancement of EG-binding and appearance of E-binding activity after 10-20 min was followed by a reduction of rosette-forming cells (RFC) with a minimum at about 1 hr and then by an increase of both E-RFC or EG-RFC up to 5 hr. Simultaneous incubation of M phi with trypsin and cycloheximide abrogated the second rise of binding activity and abolished binding on prolonged incubation. When these cells were washed and further incubated in fresh medium, they regained their initial E- and EG-binding capacity after 4-5 hr incubation. Taken together, these results are consistent with the idea that rat M phi bear a ganglioside receptor-like structure which seems to be a membrane protein and which is modulated by enzyme treatment.