MEASUREMENT OF CELLULAR MICROBICIDAL ACTIVITY AGAINST PNEUMOCYSTIS-CARINII IN-VITRO

As Pneumocystis carinii cysts cannot be cultivated for enumeration of colony forming cells, two alternative approaches to measuring killing of P. carinii by mouse peritoneal cells were investigated. The cells t ested were either normal resident peritoneal cells, or cells which wer e elicited by intraperitoneal injection of the bacterium Listeria mono cytogenes. The latter population showed enhanced antibacterial activit y against Listeria organisms and enhanced production of H2O2 in the pr esence of P. carinii, cysts from immunosuppressed rats. To assess kill ing of P. carinii, cysts were mixed with peritoneal cells at a ratio o f 10:1, and after intervals of incubation the peritoneal cells were ly sed by saponin treatment. The viability of the cysts was assessed by s taining with vital dyes or by uptake of tritiated uridine over 7 h inc ubation. Viability of cysts was unaffected by saponin treatment, and t here was agreement between the two techniques that the elicited perito neal cells killed approximately twice the number of cysts over a 20 h incubation period compared to normal resident peritoneal cells.