Isocyanate-conjugated human lung epithelial cell proteins: A link between exposure and asthma?

Background: Isocyanates are a group of highly reactive cross-linking chemic als that cause airway inflammation and asthma in exposed individuals. Isocy anates have been detected along the airway epithelia of exposed workers and animals, prompting the hypothesis that isocyanates can directly bind to ep ithelial cell proteins. Objective: We tested the hypothesis that hexamethylene diisocyanate (HDI) b inds directly to lung epithelial cell proteins and initiated studies to eva luate the immunostimulatory potential of HDI-conjugated lung epithelial cel l proteins. Methods: Human lung epithelial cell lines were exposed to vapor- and liquid -phase HDI, and the cellular proteins were analyzed for HDI conjugation by Western blotting and tested for the ability to induce lymphocyte proliferat ion in vitro. Results: A number of epithelial cell polypeptides, ranging from 25 to 110 k d in apparent molecular weight, were conjugated with HDI after exposure of the human lung epithelial cell lines (A549 and NCI-H292) to HDI concentrati ons greater than 0.005% (vol/vol) in the liquid phase. Vapor-phase HDI expo sure resulted in a more restricted HDI conjugation pattern, with major HDI- conjugated polypeptides migrating at 47, 71, and 91 kd, HDI-conjugated epit helial cell proteins specifically stimulated proliferation of PBMCs from su bjects with isocyanate induced asthma but not HDI-exposed nonasthmatic indi viduals or atopic subjects with nonisocyanate-related asthma. Conclusions: The data demonstrate that epithelial cell proteins readily rea ct with HDI and that HDI-conjugated epithelial cell proteins can stimulate lymphocyte proliferation. Further characterization and evaluation of HDI-co njugated epithelial cell proteins will elucidate their potential role in th e pathogenesis of isocyanate-induced asthma.