Abstract

Background The structural characteristics of diisocyanate chemical protein antigens vary depending upon the methods of production, and may influence diisocyanate antigen immunoassays. The impact of different antigen preparation methods on immunoassay sensitivity, specificity, and predictive value for identifying workers with diisocyanate asthma (DA) has not been systematically evaluated.

Objective Evaluate the influence of preparation methodology of hexamethylene diisocyanate human serum albumin (HDI–HSA) conjugates on the performance of specific antibody assays for identifying workers with confirmed HDI asthma.

Methods Asthmatic reactions to HDI exposure were assessed in 80 autobody shop workers by specific inhalation challenge (SIC). HDI-specific IgE and IgG in serum were measured by RAST and ELISA with seven different HDI–HSA conjugates prepared in liquid phase with monomeric or polymeric HDI, or vapour-phase monomeric HDI. The HDI : HSA substitution ratios were determined by mass spectrometry.

Results DA was confirmed by SIC in 23 subjects. The maximal sensitivity for detecting specific IgE among workers with positive SIC results was higher with RAST and with polymeric vs. monomeric HDI–albumin conjugates (21.7% vs. 8.7%) with a generally high specificity (95%). HDI–HSA specific IgG antibody was also detected in 22–43% of HDI asthmatics depending upon the conjugate used. The specificity of specific IgG varied from 88% to 96%, and it was higher for monomeric (vs. polymeric) HDI–albumin conjugates with low (vs. high) substitution ratios.

Conclusion The test performance of specific IgE and IgG immunoassays for identifying a positive SIC response varied with different HDI–HSA conjugates. Standard test antigens and common immunoassays must be used to minimize inter-laboratory variability.

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