Muramyl dipeptide increases tolerance to shock and bacterial challenge in mice.

We measured the phagocytic capacity of the reticulo-endothelial system by assay of the clearance of colloidal carbon from the blood stream in both normal mice and mice in which shock had been induced by intraperitoneal injection of hypertonic glucose. The group of shocked mice was further subdivided into those pretreated with the immunoadjuvant, muramyl dipeptide (MDP), and those given placebo. Shock reduced reticulo-endothelial phagocytosis (P less than 0.01), whereas pretreatment of shocked mice with MDP led to a hyperphagocytic state (P less than 0.01). In a second series of experiments we subjected shocked mice, pretreated with MDP or placebo, to a virulent Klebsiella pneumoniae infection. MDP significantly improved survival (P less than 0.01).