Comparison of histological and immunological techniques for detection of Pneumocystis carinii in rat bronchial lavage fluid.

We compared histological and immunological techniques in the early diagnosis of Pneumocystis carinii pneumonia in bronchial lavage fluid of steroid-treated rats. The rats were sacrificed weekly and lavage fluids were: (i) examined with cresyl echt violet and Giemsa stains; (ii) examined for P. carinii antigens by indirect fluorescent-antibody, counterimmunoelectrophoresis, and double-diffusion techniques, using high-titer spectific antisera to P. carinii raised in rabbits. P. carinii was detected in lavage fluid by cresyl echt violet at 2 weeks of steroids and persisted even with steroid tapering; the intensity of the infection in lavage fluid closely paralleled that in the lungs. P. carinii was not detected in lavage by Giemsa stain until 4 weeks and disappeared from the fluids with steroid tapering. P. carinii was detected by indirect fluorescent antibody as early as 1 week of steroids, and the results correlated well with those of cresyl echt violet. P. carinii antigens were not detected in lavage fluids or serum by counterimmunoelectrophoresis or double-diffusion techniques. Although precipitin lines sometimes occurred, they were nonspecific. In this model, cresyl echt violet and indirect fluorescent antibody were the preferred techniques for the early diagnosis of P. carinii infection in bronchial lavage fluid.