Pneumocystis carinii pneumonia is the leading cause of death in AIDS patients. During P. carinii development, the outer membrane of the newly excysted trophozoite gradually begins to acquire an electron-dense outer coat. Fully developed, the cyst bears a prominent electron-lucent space and a heavily coated, carbohydrate-rich outer membrane exhibiting antigenic activities. Several glycoproteins, including a 116 kDa and a 45-50 Kda species, along with alpha- and beta-glucans, account for the cyst wall carbohydrate content (8%). The structure of P. carinii carbohydrates during the development of the outer membrane coat, and after maturation, has not been elucidated. What are the structures of the oligosaccharide chains of the glycoproteins? What are the structures of the glucans, and how are they associated with the wall glycoproteins? Do trophozoites exhibit a unique antigenic pattern from mature cysts, and is this variation do to differences in glycosylation patterns? Are there antigens specific for P. carinii in human lungs versus rat lungs? Do the surface glycoproteins directly interact with CD4+T cells, and if so, do carbohydrates play a significant role in this interaction? Is there more than a structural role to the glucans? The proposed study will address these questions by: 1. Determining the structures of the oligosaccharide chains of gp116 and gp45-50, obtained from rat and human P. carinii trophozoites and cysts. 2. Completely characterizing the structure of the glucans and other polysaccharides found in the wall of P. carinii. 3. Comparing antigenic patterns and structural differences in carbohydrates of isolated mature cyst and trophozoite glycoproteins, and of rat versus human lung P. carinii. 4. Examining whether P. carinii surface glycoproteins and/or carbohydrates bind to CD4+T cells. The overall objective of the proposed studies is to analyze the carbohydrate structures of P. carinii cyst and trophozoite surface antigens by comparing glycosylation patterns of both developmental stages, and to determine if these carbohydrates are involved in mediating host cellular responses. The data obtained will further our understanding of the interactions of P. carinii surface molecules with host cells and be valuable in scheming new therapeutic tactics to combat P. carinii pneumonia in AIDS patients.