Indirect assessment of 4,4'-diphenylmethane diisocyanate (MDI) exposure by evaluation of specific humoral immune responses to MDI conjugated to human serum albumin.

Background: A study of occupational asthma among workers exposed to 4,4'-Diphenylmethane Diisocyanate (MDI).

Objective: To demonstrate if serum concentrations of MDI-specific IgG or IgE are sensitive biological markers of disease or of MDI exposure.

Methods: The study group consisted of nine MDI-exposed workers and nine nonexposed workers. Air sampling for MDI and polymethylene polyphenyl isocyanate, occupational and medical histories, respiratory physical exams, pre- and postshift spirometry, and self-administered peak expiratory flow rates were performed. Serum specific IgE and IgG antibodies to an MDI-human serum albumin (HSA) conjugate were assayed by the radioallergosorbent test and the enzyme-linked immunosorbent assay, respectively, and compared to nine nonexposed laboratory controls.

Results: No definitive cases of occupational asthma were documented. The mean level of MDI-specific IgG was significantly greater among exposed workers compared to nonexposed workers and laboratory controls (p = 0.04). Mean levels of TDI and HDI-specific IgG were also increased.

Conclusion: This study demonstrates that serum concentrations of MDI-specific IgG appear to be a moderately sensitive biological marker of MDI exposure, but not an indicator of occupational asthma. Workers with IgG antibodies specific for one diisocyanate-HSA conjugate exhibit cross-reactivity to antigens prepared with other diisocyanates.