Immunoactive peptides, FK-156 and FK-565. III. Enhancement of host defense mechanisms against infection.

We investigated the effect of immunoactive peptides, FK-156 and FK-565 on host defense mechanisms against microbial invasion. It was shown that these drugs given to normal mice increased the counts of phagocytes in both peripheral blood and peritoneal cavity, and enhanced the chemotactic, phagocytic and killing activities of peritoneal macrophages and polymorphonuclear leukocytes, and stimulated the phagocytic function of the reticuloendothelial system. Enhanced host resistance to microbial infection by these immunoactive peptides might be induced by both increase in counts and enhancement of functions of phagocytes. FK-156 restored decreased counts and functions of phagocytes in mice immunosuppressed by cyclophosphamide, hydrocortisone or tumor. These findings suggest that these immunoactive peptides could be applied to prevent intractable infection in immunocompromised hosts.