Effect of cessation of exposure to toluene diisocyanate (TDI) on bronchial mucosa of subjects with TDI-induced asthma

The effect of cessation of exposure to toluene diisocyanate (TDI) was studied in six patients with TDI-induced asthma, proved by a positive inhalation challenge with TDI. Bronchial challenges with TDI and methacholine were performed, and lobar bronchial biopsies were taken at diagnosis and 6 months later, after cessation of exposure. Biopsies from four nonasthmatic control subjects were also examined. At diagnosis, asthmatic subjects had thickened reticular basement membrane (p <0.05) and increased numbers of mononuclear cells (p <0.05) and eosinophils (p <0.05) in the lamina propria when compared with control subjects. Electron microscopy showed degranulation of eosinophils and mast cells in asthmatics. Six months after cessation of exposure, the thickness of reticular basement membrane was significantly reduced compared with that at diagnosis (p <0.05), and it decreased to values similar to those of control biopsies. Inflammatory cell numbers in bronchial mucosa of asthmatic subjects did not change significantly 6 months after removal from exposure, and degranulation of eosinophils and mast cells was still present. At the end of the study, airway hyperresponsiveness to methacholine and/or sensitivity to TDI persisted in most of the asthmatic patients despite the cessation of exposure and the disappearance of asthmatic symptoms. In conclusion, in patients with occupational asthma induced by TDI, the avoidance of exposure to the sensitizing agent for 6 months is able to reverse the reticular basement membrane thickening in the bronchial mucosa, but the inflammatory cell infiltrate, the specific sensitivity to TDI, and the nonspecific airway hyperreactivity may persist.