[Effect of glucocorticoid on lung tissue and bronchus-associated lymphoid tissue of experimental granulomatous lung]

The effect of glucocorticoid on the immunological response in the delayed type hypersensitivity reaction of granulomatous disorders was investigated in order to elucidate the mechanism of glucocorticoid on the suppressive course of the reaction. Experimental pulmonary granuloma model in rats was induced by an intravenous injection of heat killed BCG, and the effects of methylprednisolone (MPSL) on the granulomatous lung tissue, bronchus associated lymphoid tissue (BALT) and the population of cells from bronchoalveolar lavage fluid (BALF) and peripheral blood were examined by the cytological and immunohistochemical methods. The pulmonary granulomatous reaction was reduced effectively by the administration of MPSL. A remarkable reduction of the number of Ia antigen positive alveolar macrophages (Ia+ A.M phi) and T lymphocytes in the granulomatous lung tissue and BALF was observed. T helper cells to non-helper cells (TH/TNH) ratio in BALF decreased remarkably. Furthermore, a reduction of Ia antigen positive macrophages (Ia+ M phi) and T cells was noted in the parafollicular area of BALT. These findings suggest that glucocorticoid may suppress the immunological activity of M phi and T cell through its inhibitory effect on the differentiation of Ia+ M phi and activated T cells, which result in the diminishment of pulmonary granulomatous reaction through the disorder of M phi - T cell interaction. On the other hand, lymphocytopenia with decreased TH/TNH ratios in peripheral blood was observed simultaneously with the reduction of the pulmonary granulomatous reaction. Thus, the mechanism of reduced pulmonary granulomatous reaction after MPSL administration may be not only due to local immunosuppression, but also to impaired systemic immune response. In addition, the disappearance of the germinal center and the reduction of surface IgM-positive cells in the follicular area of BALT occurred with the reduction of pulmonary granulomatous reaction. These results suggest that glucocorticoid also suppress the humoral immune responses in BALT during the course of delayed type hypersensitivity reaction.