Comparison of histologic and quantitative techniques in evaluation of therapy for experimental Pneumocystis carinii pneumonia.

Pneumocystis carinii pneumonia was induced in rats by the administration of corticosteroids, and histologic and quantitative techniques were compared in the evaluation of the severity of the disease and response to therapy. A highly significant correlation was found between the histologic score of the extent of alveolar involvement (the standard method of assessment) and the number of P. carinii cysts and nuclei in lung homogenates, lung weight, and lung weight/body weight ratio. Clear differences were noted between rats which responded well and rats which responded poorly to therapy by all techniques. Quantitation of P. carinii cysts and nuclei revealed a 10(4)-fold reduction in organism burden with successful treatment. Thus, these techniques should be helpful in the development of testing of new antimicrobial agents in the rat model of pneumocystosis.