Western blot analysis of HPLC purified airway surface fluid. Airway surface fluid from human lung and a human bronchial xenograft model was extracted, lyophylized, resuspended in water, and fractionated over an HPLC column. Fractions that showed antimicrobial activity and positive immunoreactivity with the anti-LL-37/hCAP-18 antibody in dot blot analysis were analyzed by Western blot. Shown are the results of the Western blot for fractions 35 and 36 from the xenograft (XG) and 57 to 60 from human lung (Lung). The control is 40 ng of synthetic LL-37 (lane LL); 20 μg of a low molecular weight fraction from total mouse lung was loaded into lane ML. Bars along the left border indicate molecular mass markers of 2.3, 3.4, 6.5, 14.3, 21.5, 30.0, and 46.0 kDa.