Induction of tumoricidal macrophages and production of cytokines by synthetic muramyl dipeptide analogues

The ability of various synthetic muramyl dipeptide (MDP) derivatives to induce the production of interleukin-1 (IL-1) and colony stimulating factor (CSF) in vitro and in vivo and to induce cytotoxic macrophages was studied. 6-O-L18-MDP(Me) and MDP-Lys(L18), which were potent inducers of IL-1 and CSF production and of cytotoxic macrophages, had protective activity against Sendai virus infection in mice. In contrast, 1-O-L18-(6-O-P)-MDP(Me) and 2-N-L18-MDP exhibited weak or no ability to induce IL-1 and CSF production and no induction of tumoricidal macrophages, and did not protect against infection of Sendai virus. MDP derivatives, except 2-N-L18-MDP, efficiently rendered macrophages cytotoxic against target cells in the presence of murine recombinant interferon-gamma in vitro. The derivatives that induced cytokines and cytotoxic macrophages appeared to produce anti-viral activity.