IMMUNOHISTOCHEMICAL DETECTION OF TOLUENE DIISOCYANATE (TDI) ADDUCTS IN PULMONARY TISSUE OF GUINEA-PIGS FOLLOWING INHALATION EXPOSURE

Toluene diisocyanate (TDI) is currently the most prevalent cause of oc cupational asthma. Inhalation of vapors of the reactive chemical may r esult in irritation and inflammation of the respiratory tract as well as in pulmonary sensitization. Although numerous studies have characte rized the pulmonary inflammation, the mechanism underlying sensitizati on remains controversial. This investigation sought to address the pro blem by following the localization of TDI in the respiratory trace of guinea pigs using a well-characterized animal model that displays both immunologic and respiratory hypersensitivity to TDI. Non-anesthetized and minimally restrained guinea pigs were exposed to a sensitizing re gimen of TDI that consisted of inhalation of 1.0 ppm TDI vapor for 3 h /day on 5 consecutive days. Pulmonary inflammation was present in anim als sacrificed immediately following the exposure as evidenced histolo gically, and by increased protein and inflammatory cells in the bronch oalveolar lavage. Using a specific and sensitive rabbit antiserum prep ared to TDI-keyhole limper hemocyanin, the presence of TDI adducts in respiratory tissues was investigated. TDI adducts were detected primar ily in the apical region of the epithelium of the nares, trachea, bron chi, and bronchioles. The amount of adduct was greatly reduced in anim als sacrificed 18 days later. Sensitized guinea pigs that were challen ged on day 23 with 80-250 ppb TDI demonstrated the same distribution o f TDI adducts as did sham-exposed animals similarly challenged. These results are the first to employ immunohistochemistry to detect TDI add ucts in respiratory tract tissue. Findings indicate that one exposure to the chemical results in detectable adducts, and that the location o f adducts is dependent upon both the concentration of TDI inhaled and the number of exposures. Isolation and characterization of the cellula r adducts should assist in elucidation of the role of adducts in the s ensitization process.