Pepsin like enzyme in macrophages and its role in the immune system.

Phagocytosis by DBA/2 or autoimmune NZB mouse macrophages of sheep erythrocytes, which are heterologous to these macrophages, was enhanced by mouse pepsin, whereas phagocytosis of homologous erythrocytes was suppressed by pepsin. Antibody production by DBA/2 or NZB mouse lymphocytes against heterologous erythrocytes was also enhanced by pepsin, but autoantibody production by NZB mouse lymphocytes was suppressed by pepsin. An acid protease present in macrophages was found to have biochemical properties quite close to those of pepsin, with regard to molecular weight, isoelectric point, and 50% inhibition dose of pepstatin. This acid protease was immunochemically identical with pepsin, reacting with anti-pepsin antibody. Taken together, these results indicate that pepsin modulates macrophage functions and that the pepsin like enzyme in macrophages may play important roles in the regulation of phagocytosis by macrophages and in antibody production.