RESULTS:Lung Function: After 24 hours, WTC-PM aspiration in WT mice produces loss of FEV, decreased compliance, and increased resistance, tissue damping, and methacholine hyperreactivity. After 28 days, lung measures improve but hyperreactivity persists. RAGE-/- are protected from these WTC-PM effects at both time points. Impedance analysis shows that changes occur in the small airways of WT exposed to WTC-PM. Histopathology: Neutrophilia is seen at 24 hours in both WT and RAGE-/- BAL. At 24 hours, area fraction trended higher in those exposed to WTC-PM, and had significantly shorter mean chord lengths. After 28 days, WT mice showed acute on chronic changes in lung architecture, and had significantly higher area fraction and shorter chord lengths. RAGE-/- mice did not show a difference in measures of lung quantification after 24 hours or 28 days.