Containment as a mechanism of nonspecific enhancement of defenses against bacterial infection.

Observations made during the study of nonspecific enhancement of antimicrobial host defenses permitted some physiologic dissection of the anatomic basis for normal protective processes. Local growth of bacteria in the hind limb in muramyl dipeptide-treated mice was suppressed modestly, but lymphatic filtration was markedly improved, especially between the ipsilateral groin and iliac lymph nodes. Spontaneous containment, when it occurred in saline-treated controls, proceeded similarly. Certain regional lymph nodes acted to restrict the dissemination of bacteria from an anatomically isolated infection, reducing the degree of bacteremia and improving survival. Containment of local bacterial infection appears more important in a favorable host response than does dispersion and is accentuated by muramyl dipeptide.