Properties of the major antigens of rat and human Pneumocystis carinii.

The major rat and human Pneumocystis carinii antigens were analyzed for their susceptibility to treatment with enzymes and other procedures by immunoblotting, immunofluorescence, and light microscopy. Carbohydrate residues were further analyzed by lectin-binding experiments. The 116-kilodalton (kDa) band of rat P. carinii was susceptible to proteolytic (e.g., trypsin) and glycolytic (e.g., Zymolyase) treatments but not to a variety of other procedures (e.g., lipase). This moiety reacted strongly with concanavalin A and wheat germ agglutinin, indicating the presence of mannosyl or glucosyl and N-acetylglucosamine residues. Immunofluorescence staining and surface labeling suggested that the 116-kDa antigen was located on the P. carinii cell wall. The 45- and 50-kDa bands were as sensitive as the 116-kDa band to degradative treatments when studied after immobilization onto nitrocellulose but were more resistant to proteolytic enzymes when studied in situ on whole organisms. These moieties exhibited poor binding to lectins and reactivity by surface-labeling procedures. The 116-kDa band of human P. carinii appeared to be a glycoprotein with characteristics similar to those of its counterpart in rats, whereas the human P. carinii 40-kDa band exhibited protein and carbohydrate properties more closely related to those of the 45- and 50-kDa rat-derived antigens. We conclude that P. carinii antigens are complex glycoproteins and that this information will be helpful in developing strategies for their isolation and purification and study of their function.