Effect of proteolytic enzymes on Pneumocystis carinii in rat lung tissue

Rat lung homogenates heavily infected with Pneumocystis carinii were digested with trypsin and pronase. Pneumocystis carinii cysts were examined by light and electron microscopy, and by an indirect fluorescent antibody (IFA) technique. Cysts digested with trypsin exhibited swelling of their cell wall but stained brightly by IFA; cysts digested with pronase lost their cell wall and ability to stain by IFA. These effects were related to the concentration of the enzyme and duration of exposure. The data suggest that the antigenic determinants of P. carinii cysts reside in the cell wall.