An enzyme-linked immunosorbent assay for enumeration of Pneumocystis carinii in vitro and in vivo.

An enzyme-linked immunosorbent assay (ELISA) to quantitate Pneumocystis carinii organisms from culture supernatant and rat lung has been developed. A polyclonal antibody specific to P. carinii was produced in Sprague-Dawley rats by allowing P. carinii-infected animals to recover from infection. This antibody reacted strongly to P. carinii proteins of 50 to 55 kDa and weakly to those of 33 and 116 kDa. The ELISA used this convalescent-phase antibody to quantitate the number of P. carinii organisms in lung homogenates of infected rats and supernatants from infected tissue cultures which were used to screen drugs for P. carinii. The results of the ELISA were compared with those of direct microscopic counting of organisms, and the two methods were highly correlated (r > 0.9). Thus, the ELISA can be used as an alternative method for the quantitation of P. carinii organisms, and it is superior to the conventional microscopic method because it is easier to perform and less labor-intensive.