Increased neutrophils in BAL fluid from SP-A^–/– mice after RSV infection. Cytospin preparations of BAL fluid were stained with Diff-Quik to identify macrophages, lymphocytes, and polymorphonuclear leukocytes. (a) The percentage of neutrophils in BAL fluid was significantly greater 3, 5, and 7 days after administration of 10⁷ pfu RSV to SP-A^–/– (filled bars) compared with SP-A^+/+ (hatched bars) mice. (b) Percentages of lymphocytes in BAL fluid were not different between the two groups. Data are mean ± SEM with n = 9 mice per group. *P < 0.05 compared with SP-A^+/+ mice. PMNs, polymorphonuclear leukocytes.