Bronchoalveolar cellular infiltration 24 h after LPS challenge. Mice were challenged i.n. with 100 μg of LPS followed 18 h later by fMLP (200 nM in 40 μL PBS). Five hours later, mice were sacrificed, and bronchoalveolar lavage collected. (a) Cells were counted using a hemocytometer. Data is shown as means ± S.E.M. ( mice per group) of a representative experiment. (b) Cells were spun unto glass slides, stained with Giemsa and observed under microscopy. Shown are representative images from a control mouse and a mouse with ALI. Note the presence of numerous neutrophils in the BAL of the ALI mouse. (c) NE activity in the bronchoalveolar lavage fluid (BALF) was measured using the MeOSu-AAPV-AMC fluorometric substrate. Reactions were monitored at various time points at excitation/emission wavelengths of 400/505 nm using a fluorescence microplate reader. Shown is the released fluorescence after subtracting background fluorescence of the substrate only.