[Pepsin-like enzyme of the macrophages and the immune system].

Pepsin enhanced phagocytosis of heterologous red blood cells by macrophages, but suppressed phagocytosis of homologous red blood cells. Antigen-presenting ability of the macrophages pulsed with heterologous red blood cells was augmented by pepsin, but not those pulsed with homologous red blood cells. On the other hand, an acid protease was found in macrophages that had biochemical and immunochemical properties which were quite close to those of pepsin. Along with phagocytosis of heterologous red blood cells by macrophages, the activity of this pepsin-like enzyme in macrophages showed an increase and extracellular release was also observed. Such changes were not observed in the macrophages that phagocytized homologous red blood cells or non-antigenic materials. Inhibition of this enzyme activity by pepstatin resulted in suppression of the phagocytosis of heterologous red blood cells. These results indicate that pepsin modulates macrophages functions and that a pepsin-like enzyme in macrophages plays an important role in the facilitation of phagocytosis and antigen-presentation by macrophages.