In vitro recognition of 'old' blood cells by macrophages from syngeneic mice: Characteristics of the macrophage-red blood cell interaction

Macrophages recognized and phagocytized 'old' but not 'young' red blood cells (RBC) from syngeneic mice in vitro via a trypsin-sensitive receptor on the macrophage surface. EDTA and EGTA (0.002 M) inhibited phagocytosis, indicating a requirement for Ca²⁺ ions. Both colchicine (10^-5 M) and cytochalasin B (5 μg/ml) inhibited phagocytosis, suggesting an important role for microtubules and microfilaments in the phagocytic process. Cellular metabolic activity was required because sodium azide (0.01 M) inhibited phagocytosis. Phagocytosis was not markedly inhibited, however, by the following sugars (up to a concentration of 0.05 M): D-glucose, D-galactose, D-mannose, L-fucose, α-methyl mannoside, D-glucosamine, N-Ac-D-galactosamine, lactose or mellibiose. Both mannan (0.1 mg/ml and 1 mg/ml) and guar (1 mg/ml), a galactomannan, had little effect on phagocytosis. In addition, there was no specific inhibition of phagocytosis by the following sugar phosphates: D-glucose-6-phosphate, D-galactose-6-phosphate, D-mannose-6-phosphate, D-fructose-6-phosphate, D-fructose-1-phosphate, D-fructose-1,6-diphosphate and D-ribose-5-phosphate. These results suggest that the recognition of old RBC by macrophages is not mediated by a specific receptor on the macrophage surface which can interact with any of the sugars or sugar phosphates tested.