Caspase-3 and caspase-8 in the lungs of mice with L. pneumophila. Wild-type and Fas-deficient mice were infected intratracheally with approximately 106 CFU/mouse of L. pneumophila. One group was kept in room air condition and another group was placed in a hyperoxic condition. Lungs were removed and homogenized at 48 hours after the infection. Caspase activity was quantified by the ELISA, as described in materials and methods. The white column represents the results of the lungs of wild-type mice whereas the filled column represents the results of Fas-deficient mice (n = 5). *P<0.01, compared to those of wild-type mice.