Bronchoalveolar lavage fluid from asthmatic subjects is mitogenic for human airway smooth muscle

Airway smooth muscle proliferation may contribute to the airway wall remode ling seen in asthma. In this study we tested for the presence of airway smo oth muscle mitogenic activity in bronchoalveolar ravage (BAL) fluid obtaine d from 12 atopic asthmatics before and serially after segmental allergen ch allenge, and from four normal subjects who did not undergo allergen challen ge. Mitogenic effect was assessed by coincubating BAL fluid with human airw ay smooth muscle cells, and measuring its effect on (3)[H]thymidine incorpo ration and cell number. Induction of ERK phosphorylation and cyclin D-1 pro tein abundance were also assessed. Compared with serum-free medium alone, B AL fluid obtained from normal subjects increased thymidine incorporation, c ell number, ERK phosphorylation, and cyclin D-1 abundance. BAL fluid from a sthmatic subjects prior to allergen challenge induced even greater increase s in all measures, except for cell number, which was similar to that observ ed with normal subjects' BAL fluid. Incubation with ravage fluid obtained 4 8 h after segmental allergen challenge in atopic asthmatics caused yet furt her increases in thymidine incorporation, cell number, and cyclin D-1 prote in abundance. Molecular sieving of prechallenge BAL fluid from three asthma tic subjects demonstrated that mitogenic activity was present exclusively i n the > 10 kD fraction. These results provide the first direct demonstratio n that fluid lining the airways of asthmatics contains excess mitogenic act ivity for human airway smooth muscle, and that this activity increases furt her after allergen challenge.