Specific IgG response to monomeric and polymeric diphenylmethane diisocyanate conjugates in subjects with respiratory reactions to isocyanates

Background: Isocyanates are a frequent cause of occupational asthma and can also induce hypersensitivity pneumonitis. Objectives: It is still unclear whether antibodies to diphenylmethane diiso cyanate (MDI), which are elicited in some subjects with these conditions, a re specific for this type of isocyanate, Moreover, preparation of conjugate s to human serum albumin (HSA) with the polymeric formulation rather than m onomeric MDI might result in improved detection of antibodies. Methods: We addressed these issues by testing the sera of 13 subjects with asthma (n = 12) and hypersensitivity pneumonitis (n = 1) induced by MDI (n = 4 or 5, see below) by comparing them with sera obtained from subjects wit h occupational asthma caused by toluene diisocyanate (TDI; n = 5) and hexam ethylene diisocyanate (HDI; n = 2), Conjugate preparations were compared by using SDS-PAGE, absorbance spectral analysis, and isolectric focusing. Imm unologic screening was done by ELISA. Results: Specific IgG antibodies that recognize MDI-HSA conjugates mere det ected in all but 1 of the MDI-exposed workers and could not be found in TDI -exposed and HDI-exposed workers, The levels of specific IgG antibodies wer e more elevated when tested against the HSA conjugates formed with polymeri c MDI compared with the HSA conjugates formed with monomeric MDI, Conclusion: This study shows that specific IgG antibodies to MDI appear to be specific for MDI without cross-reactivity with TDI and HDI and higher by use of polymeric rather than monomeric MDI-HSA test antigens.