Experimental hypersensitivity pneumonitis in rabbits induced by Trichosporon cutaneum: role of local cellular and humoral immune responses.

We evaluated the immunopathologic properties of Trichosporon cutaneum, an important etiologic agent of summer-type hypersensitivity pneumonitis in Japan. Rabbits were sensitized and challenged by either a culture-filtrate antigen or a particulate antigen prepared from a TIMM 1318 strain of the fungus. Group 1 animals received repetitive intratracheal injections of a particulate T. cutaneum antigen without use of any adjuvant. Group 2 animals were sensitized by foot-pad injections of particulate antigen followed by an intratracheal challenge with the same antigen. Group 3 animals were sensitized by a culture-filtrate antigen emulsified in Freund's incomplete adjuvant followed by a challenge with the intratracheal injection of the same antigen. In group 1, we observed interstitial pneumonitis with prominent granulomatous reactions which resembled those in human hypersensitivity pneumonitis. Group 2 animals also showed granulomatous inflammation in a some minor extent, but they were accompanied with excessive infiltration of neutrophils. In contrast, group 3 showed mild alveolitis in a cell population consisting predominantly of macrophages. Lymphocytes from mediastinal nodes responded to the antigen in groups 1 and 2 but not in group 3. Interestingly, the specific IgA antibody activity in the bronchoalveolar lavage fluids (BALF) of group 1 was significantly higher than those of group 2, despite the IgG antibody activity was the same. The ratio of IgA/IgG antibody activity in individual BALF sample in these two groups correlated inversely with the grade of neutrophil infiltration. Thus, the presence of IgA antibody in the respiratory tract affects the pathological outcome.(ABSTRACT TRUNCATED AT 250 WORDS)