Some characteristics of inflammation induced by muramyl dipeptide, endotoxin, and concanavalin A.

Inflammatory reactions induced by muramyl dipeptide (MDP), endotoxin, and concanavalin A (Con A) were examined in the skin of rabbits. The neutrophil influx induced by MDP peaked at 2 h and declined to a low level by 4 h, thus resembling the response induced by endotoxin. MDP and endotoxin exhibited homologous desensitization when extant lesions were restimulated at 6 h. These agents did not, however, induce heterologous desensitization. Con A induced a biphasic influx of neutrophils into inflammatory lesions with peaks at 2 h and 12 h. Neither the first nor second peak exhibited desensitization to homologous restimulation; however, the cell influx in restimulated lesions assumed a monophasic character peaking at 3 h. Con A lesions were not desensitized to restimulation with MDP or endotoxin. The results suggest that these chemotaxinogens rely on different endogenous mediators to induce an inflammatory response. The protracted second period of neutrophil infiltration of Con A-induced lesions and the failure of desensitization of this response to develop suggest that the mediator of Con A-induced inflammation may play an important role in the sustained recruitment of neutrophils in some inflammatory diseases.