Respiratory hypersensitivity in guinea pigs sensitized to 1,6-hexamethylene diisocyanate (HDI): comparison of results obtained with the monomer and homopolymers of HDI.

This study used guinea pigs that were sensitized to the biuret or isocyanurate type homopolymers of 1,6 hexamethylene diisocyanate (HDI). Induction was either by intradermal injection or repeated inhalation exposures. For comparison, groups of guinea pigs were sensitized to monomeric HDI. Naive animals served as negative controls. Two and three weeks following induction, animals were challenged by inhalation with the hapten and homologous protein conjugate of the hapten, respectively. Assessments were based on changes in respiratory rate, serum IgG(1)-antibody titer, and influx of eosinophilic granulocytes in airways. Guinea pigs induced and challenged with the HDI-monomer did not display appreciable changes in respiratory rate, whilst the re-challenge with the HDI-protein conjugate caused unequivocal changes in respiratory patterns, including a marked bronchial influx of eosinophilic granulocytes. In contrast, animals induced and challenged with either the free or conjugated aerosols of HDI-homopolymers failed to elicit specific physiological or morphological pulmonary responses. IgG(1) antibodies were observed in all groups receiving monomeric HDI or HDI-homopolymers. Based on the comparative assessment of antibody titers following intradermal injections, it appeared that monomeric HDI was more potent to induce specific IgG(1) antibodies than the homopolymers of HDI. In summary, with respect to induction of allergy and asthma, the data presented here suggest that the homopolymeric forms of HDI appear to be less potent asthmagens, if any, than monomeric HDI.