Immunoactive peptides, FK-156 and FK-565. I. Enhancement of host resistance to microbial infection in mice.

The protective effect of an immunoactive peptide, D-lactoyl-L-alanyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl-(L)-glycine (FK-156) and a related compound, heptanoyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl-(D)-alanine (FK-565) was determined in mice with various kinds of microbial infections. FK-156 and FK-565 were given to mice either subcutaneously or orally before challenge. The drugs enhanced significantly the defense of mice against acute systemic infections induced by various extracellular and facultative intracellular organisms, and subcutaneous abscess by Staphylococcus aureus. The protective effect of these drugs against Escherichia coli infection differed considerably depending on the route of administration; FK-156 was only effective by the parenteral route; however, FK-565 was effective by both parenteral and oral routes. After subcutaneous dosing with FK-156, the enhancement of host defense of mice against E. coli infection was more rapid than against Listeria infection. The enhancing effects of FK-156 and FK-565 on host defense of mice against pseudomonal infection was more potent than other immunoactive drugs.