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 occupational asthma. Inhalation of vapors of the reactive chemical may result in irritation and inflammation of the respiratory tract as well as in pulmonary sensitization. Although numerous studies have characterized the pulmonary inflammation, the mechanism underlying sensitization remains controversial. This investigation sought to address the problem by following the localization of TDI in the respiratory tract 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 regimen 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 animals sacrificed immediately following the exposure as evidenced histologically, and by increased protein and inflammatory cells in the bronchoalveolar lavage. Using a specific and sensitive rabbit antiserum prepared to TDI-keyhole limpet hemocyanin, the presence of TDI adducts in respiratory tissues was investigated TDI adducts were detected primarily in the apical region of the epithelium of the nares, trachea, bronchi, and bronchioles. The amount of adduct was greatly reduced in animals sacrificed 18 days later. Sensitized guinea pigs that were challenged on day 23 with 80-250 ppb TDI demonstrated the same distribution of TDI adducts as did strata exposed animals similarly challenged. These results are the first to employ immunohistochemistry to detect TDJ adducts in respiratory tract tissue. Findings indicate that one exposure to the chemical results in detectable adducts, and that the location of adducts is dependent upon both the concentration of TDI inhaled and the number of exposures. Isolation and characterization of the cellular adducts should assist in elucidation of the role of adducts in the sensitization process.