Polyisocyanates and Their Prepolymers

After describing the frequent use of polyisocyanates worldwide, especially in the automotive industry sector, the authors present the historical background of occupational asthma (OA) due to this category of agents. In general subjects with OA to low-molecular-weight (LMW) agents, including polyisocyanates, are at higher risk of severe asthma. The latency period for onset of symptoms in subjects who develop OA is shorter than for high-molecular-weight (HMW) agents. Currently, exposure to polyisocyanates seems to be better controlled, with fewer occurrences of OA due to this type of agent by medicolegal agencies, which probably reflects lower exposure as evidenced by air sampling and biological monitoring. Workers can get sensitized by airborne and skin exposures. Peak exposures appear as important as average exposure levels in causing sensitization and OA. The association with human leukocyte antigen (HLA) and non-HLA genes is discussed. Alteration of the epithelial layer structure by exposure to polyisocyanates plays a central role in the onset of asthma. The resulting airway inflammation is characterized by both eosinophilic and neutrophilic infiltrates in the airways. The mechanism of sensitization seems only occasionally IgE-dependent. The outcome of workers no longer exposed is similar to what is generally seen in OA: asthmatic symptoms improve but there is generally persistence of airway hyperresponsiveness. Reduction of exposure and medical surveillance programs in high-risk workplaces are satisfactory means to prevent OA due to polyisocyanates.