A. Cell proliferation following Pneumocystis infection. Blood and spleen cells were obtained 10 to 12 weeks after initial exposure to Pneumocystis-infected seeders, a time by which Pneumocystis infection has typically developed and been cleared in healthy, immunocompetent animals. Splenocytes from these animals were cultured with recombinant P. murina Msg proteins (n = 9 except n = 7 for MSG119Am), crude Pneumocystis antigens (n = 9), and purified native Msg (n = 2). Splenocytes from unexposed control animals were cultured with the same antigens (n = 4 for all except n = 3 for MSG119Am and n = 1 for native Msg). Bars represent the stimulation index (SI) as compared to proliferation to appropriate vector without Msg for recombinant antigens and normal lung antigens for crude Pneumocystis antigens and no antigen for native Msg. B. Antibody reactivity to each of the antigens measured by ELISA. Each bar represents the mean optical density of the Pneumocystis exposed or control animals (the same number of animals were used as for A). Of note, 1 of 7 Pneumocystis exposed animals had antibodies to MSG119Am. Unpaired t tests were used to compare the results for exposed animals to control (unexposed) animals. Statistical significance is indicated by the following symbols: *, p ≤ 0.05; ‡, p ≤ 0.01; †, p ≤ 0.001. For native Msg (left panel) statistical significance was not calculated due to the small number of animals.