Fractionation of Pneumocystis carinii antigens used in an enzyme-linked immunosorbent assay for antibodies and in the production of antiserum for detecting Pneumocystis carinii antigenemia

Cyst-rich suspensions of Pneumocystis carinii were obtained by differential and gradient centrifugation from heavily infected rat lungs. After preparation of an aqueous-soluble extract of the cyst-rich material, the insoluble residue was extracted with 8 M urea. Small amounts of infected human lung tissue and uninfected rat and human lung were processed similarly. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that both human and rat infected lung extracts contained a large protein (greater than 200,000 daltons). This component was not present in extracts of uninfected lung. In addition, an HCl-soluble extract was prepared from the cyst-rich suspension from infected rat lung. The urea-extracted antigen was most reactive in an enzyme-linked immunosorbent assay. Rabbit antiserum against the HCl-soluble antigen detected circulating antigen in patients' sera in a counterimmunoelectrophoresis assay.