Respiratory hypersensitivity to diphenylmethane-4,4'-diisocyanate in guinea pigs: comparison with trimellitic anhydride.

Published evidence demonstrates successful induction and elicitation of respiratory hypersensitivity in guinea pigs by the known human respiratory allergens trimellitic anhydride (TMA) and diphenylmethane-4,4'-diisocyanate (MDI). From these data it is apparent that TMA-related respiratory hyperresponsiveness can be elicited readily in guinea pigs upon inhalation challenge with the free chemical. Despite the interlaboratory variability in methodological procedures used for the sensitization as well as elicitation of response and the wide range of concentrations of TMA employed for challenge exposures (6-57 mg/m(3) air), TMA had been unequivocally identified as a benchmark respiratory sensitizer by measurements of the respiratory rate during challenge. The protocols were duplicated to examine the respiratory sensitizer MDI. In intradermally sensitized guinea pigs, changes in immediate-onset-like respiratory response were observed when MDI challenge concentrations exceeded approximately 30 mg MDI/m(3) air. Collective experimental evidence suggests that the respiratory responses observed upon challenge with TMA were markedly more pronounced and easier to identify than those recorded following challenge with MDI or MDI conjugate. In contrast to TMA, irritant concentrations of MDI had to be used to elicit any respiratory response and the differentiation of irritant and allergic responsiveness became increasingly difficult. Despite the absence of unequivocal changes in breathing patterns upon MDI challenge, MDI-sensitized animals displayed elevated anti-MDI immunoglobulin G1 (IgG1) antibodies, and a significant influx of eosinophilic granulocytes in the bronchial wall and lung-associated lymph nodes. Therefore, it is believed that the robustness of this animal model to identify low-molecular-weight agents as respiratory sensitizer is increased when several endpoints are considered. These are (1) positive respiratory response upon challenge with the hapten, and if negative, also challenge with the conjugate of the hapten; (2) an influx of eosinophilic granulocytes; and (3) increased specific IgG1 response. Furthermore, it appears that particles in the range of approximately 2-6 microm evoke more consistent respiratory response upon challenge exposure than particles in the 1-2 microm range.