OBJECTIVES A case is described of complex reactions associated with exposure to diphenylmethane diisocyanate (MDI), with some immunologic observations.

METHODS Medical history, clinical examinations, and analyses of immunologic parameters and the 4,4'-MDI-related amine 4,4'-diaminodiphenylmethane (MDA) in hydrolyzed serum and urine were used.

RESULTS The patient, a mechanic whose medical history suggested repeated attacks of a work-related pulmonary or systemic disease, was examined because of acute respiratory disorder, rhinoconjunctivitis, and a late systemic reaction after exposure to polyurethane pyrolysis products, including 4,4'-MDI (air level 15 micrograms.m3). Spirometry showed a partly reversible obstructive dysfunction, and a skin-prick test was positive versus isocyanates conjugated with human serum albumin (HSA). MDA was detected in hydrolyzed serum (5.6 ng.ml) and urine (1.6 micrograms.g creatinine-1). In serum, there were specific immunoglobulin (Ig) G (IgG1 and IgG4) and IgE antibodies to 4,4'-MDI-HSA and other isocyanates (phenylisocyanate, toluene diisocyanate, p-toluene monoisocyanate, hexamethylene diisocyanate) conjugated with HSA, a very high total IgE, a raised total IgG, and moderate neutrophilia and eosinophilia. The specific antibodies declined, but were still increased five years later. Furthermore, the values of circulating immune complexes were high. In vitro, the circulating immune complexes in serum increased after the addition of 4,4'-MDI-HSA. The patient had anti-Clq antibodies, which probably accounted for part of the circulating immune complexes.

CONCLUSIONS The reactions associated with MDI exposure (in combination with exposure to pyrolysis products) had features compatible with immediate hypersensitivity and with a complement-mediated immune-complex reaction.