SP-A protein levels in the lung of C57BL/6 mice were not increased following allergic challenge of sensitized mice. Western blot of three representative SP-A samples from the LA surfactant fraction of the BAL fluid of Balb/c and C57BL/6 mice (A). Nitrocellulose blots with samples of LA surfactant from naïve and sensitized mice were probed with polyclonal anti-SP-A antibody as described. Each lane contains 5 μg total protein. The relative content of SP-A doublet bands in each sample was determined by densitometric scanning of the 29–35 kD bands from multiple blots and quantified as described (B). Open bars: Naive mice; Closed bars: Sensitized mice. Data are expressed as % of naïve Balb/c levels. Mean ± SEM of n = 3–5 was calculated after deriving the average of the results from two independent experiments. # p < 0.05 C57BL/6 vs naïve Balb/c mice. The SP-A content in the LA and SA fractions of naïve mice was also determined by using an ELISA protocol as described. Total BAL SP-A content (C) was expressed as total ng. Gray bars: LA fraction of BAL; Black bars: SA fractions of BAL. Data are expressed as Mean ± SEM of n = 5 samples in each group. #p < 0.05 C57BL/6 vs naïve Balb/c mice. Total RNA for northern blot analysis was prepared from the lungs of naïve and sensitized mice as described. Intensity was quantified by densitometric scanning and values were normalized to 28S mRNA (D). SP-A mRNA contents are expressed as % of naïve Balb/c level. Open bars: Naive mice; Closed bars: Sensitized mice. Mean ± SEM of n = 3–5 samples was calculated after deriving the average of the results from two independent experiments.