Pathology produced by isocyanates: methods of immunological investigation

A group of 182 workers exposed to diisocyanates (varnishers, carpenters, producers of polyurethane resins and expanded plastic) were examined to study the immunogenic capacity of these substances. The skin tests, particularly the intradermal tests, revealed reactions of the immediate, accelerated and/or delayed types due to the presence of IgE and IgG, in addition to responses of the cellular type. This was confirmed by passive transfer in guinea-pigs and man and immunohaematological tests such as passive haemagglutination and lymphocyte transformation. In 4 cases it was possible to demonstrate thermoresistant, homocytotropic immunoglobulins, that were not dependent on complement and behaved like reagins (i.e. short-term anaphylactic IgG). Exposure tests were performed on 45 cases; the results are analyzed and compared with those of the skin tests. It is concluded that both these groups of tests are of value in investigating the aetiopathogenesis of the pathology of the isocyanates: the skin tests for initial screening, and then the exposure tests for resolving doubtful diagnoses. Cross-reactions were also demonstrated between toluene-diisocyanate and methylene-diisocyanate. Two phases could be considered in the pathogenesis; in the first phase, signs of inflammation appeared at the primary sites of contact with the irritant, then the ability of the diisocyanates to form a conjugate with organic proteins results in the production of a complete antigen and consequent sensitization of the exposed person. The appearance of symptoms naturally depends on subsequent exposure and the immunogenic capacity of the patient: the response is mainly of the reagin type in atopic patients and of type 3 in non-atopic patients.