Background: The bioreactivity of isocyanate, a leading cause of occupational asthma, has led to uncertainty regarding the chemical's antigenicity and mechanisms that elicit immunopathology.
Objective: To understand better the biologically relevant antigenic forms of hexamethylene diisocyanate (HDI), commonly used in the auto body industry.
Methods: Human albumin was exposed to HDI vapors through a novel approach designed to model the air-liquid interface of the human airway. Vapor HDI-exposed albumin was characterized by electrophoresis, chemical substitution analysis, mass spectrometry, and serology studies on auto body shop workers (N=203) and HDI asthmatics (N=11).
Results: HDI vapors caused significant changes in the shape and/or charge of human albumin, which differed from albumin exposed to liquid phase HDI, with lower isocyanate substitution ratios and distinct electrophoretic mobility. Specific sites of vapor HDI conjugation to albumin were identified at His(247) and Lys(414). Vapor HDI-exposed albumin was specifically recognized by the humoral arm of the human immune system, with a strong dependence on albumin as the carrier. Vapor HDI-exposed albumin-specific IgG titers were significantly associated with HDI exposure (P=.001), and specific IgE was detectable in 55% (6/11) of isocyanate asthmatics versus 1.5% (3/203) of exposed healthy workers. Parallel studies using HDI-exposed albumin conjugates produced by previously published methods showed less significant associations of HDI-specific IgG and IgE with exposure and disease, respectively.
Conclusion: HDI-albumin conjugates produced by novel vapor phase exposure methods may be more physiologically relevant than those produced by previously published methods and of greater utility in characterizing the immune responses associated with HDI exposure and asthma.