The Loss of Macrophages from Peritoneal Exudates following the Injection of Antigens into Guinea-Pigs with Delayed-Type Hypersensitivity

Exudates were induced in the peritoneal cavities of guinea-pigs by the injection of glycogen. The cell content of these exudates was examined after 4 days in normal and hypersensitive animals. In animals uninjected with antigens, the exudates contained a high proportion of macrophages, together with lymphocytes and polymorphs. In BCG-vaccinated animals, with delayed-type hypersensitivity to tuberculin, subcutaneous, intravenous or intraperitoneal injection of tuberculin resulted in a profound fall in the macrophage content of the exudates. This effect was apparent within an hour of intraperitoneal injection and occurred with very small doses of tuberculin. No such effect occurred after the intraperitoneal injection of tuberculin into guinea-pigs with Arthus hypersensitivity to tuberculin. Ovalbumin injected intraperitoneally into guinea-pigs with mixed delayed-type and Arthus hypersensitivity to ovalbumin also resulted in a marked fall in the macrophage content of peritoneal exudates, but had no effect on the peritoneal macrophages of animals with pure Arthus hypersensitivity. Bacterial endotoxin injected intraperitoneally caused a similar fall in the macrophage content of exudates of both normal and BCG-vaccinated animals. It is concluded that this loss of macrophages from peritoneal exudates after the injection of antigen is the consequence of an immunological reaction which is a manifestation of a state of delayed-type hypersensitivity.