Stimulatory effects of muramyl dipeptide upon neutrophils isolated from a local bacterial infection.

This study examined the effects of muramyl dipeptide (MDP) in vivo upon the local inflammatory response to a bacterial challenge. In addition to quantitative bacteriology of the tissues surrounding an infected suture, polymorphonuclear leucocytes (PMN) involved in the local inflammatory response were extracted and estimations made of their number, viability and phagocytic activity. Fewer bacteria were recovered from the muscle around the suture in MDP-treated animals compared to placebo-treated controls (P less than 0.02), although there was no difference in the number of bacteria on the suture itself. Polymorphonuclear leucocytes were present in greater numbers (P less than 0.01), more PMNs were viable (P less than 0.01) and more PMNs had visibly phagocytosed bacteria (P less than 0.01) in the MDP group compared to the placebo group. These data indicate that MDP enhances the local inflammatory response to infection with increased influx, viability and phagocytic activity of PMNs, resulting in improved local control of a test bacterial challenge.