Role of Corynebacterium parvum in the activation of peritoneal macrophages: I. Association between intracellular C. parvum and cytotoxic macrophages

We have investigated the association between intracellular C. parvum (CP) and macrophage (Mφ) cytotoxicity. Mouse peritoneal Mφs were activated by ip administration of CP and were subjected to a combination of fractionation techniques to study this. Velocity sedimentation demonstrated that only the largest cells were cytotoxic. These same cells contained CP and suggested an association between the two variables. Further separation of the largest Mφs using a BSA equilibrium buoyant density gradient demonstrated that cytotoxicity was due to Mφs and further substantiated the strong correlation between intracellular CP and cytotoxicity. Various fluorochrome tagged CP preparations were also used to activate Mφs and to isolate CP-containing Mφs using fluorescence-activated cell sorting. When velocity-enriched Mφs were sorted on the basis of the presence or absence of fluorescent CP, only the Mφ fractions which contained CP were cytotoxic. The results indicate that most cytolytic macrophages present at the peak of the response contain CP. Thus, a convenient probe with which to follow macrophage activation at the single cell level was provided.