Augmentation of protective and antibacterial activity induced by muramyl dipeptides in CBA/N defective mice with X-linked immunodeficiency for Salmonella enteritidis infection.

Stimulation of resistance induced by muramyl dipeptide (MDP) and its analog, N alpha-MDP-N epsilon-stearoyl-L-lysine [MDP-Lys(L18)], was examined in experimental salmonellosis in CBA/N defective mice with X-linked immunodeficiency to virulent Salmonella enteritidis no. 11. An injection of either MDP or MDP-Lys(L18) did not induce any effective protection, but repeated injections of MDP-Lys(L18) (100 micrograms per mouse per day for 3 days consecutively) to the mice before bacterial challenge gave some protection. Multiple injections with MDPs once a day for several days consecutively strongly increased bactericidal capacity in the peritoneal cavities and spleens of the mice. Moreover, previous injection of the MDPs could elevate the phagocytic function of the reticuloendothelial system in the defective mice. These results indicate that nonspecific resistance of CBA/N defective mice to salmonella infection can be improved by previous administrations of MDPs.