[Steroid resistance and lung-tissue cytokines in experimental bleomycin-induced lung fibrosis]

To examine the mechanism of steroid resistance in lung fibrosis, cytokines expressed in the lung tissue of mice with bleomycin-induced lung fibrosis were studied. 1. Glucocorticoid administration (1 mg/kg/day) did not affect the grade of lung fibrosis induced by intratracheal injection of bleomycin (3.76 micrograms/g). 2. Cytokines expressed in the lung tissue were studied with the reverse-transcriptase polymerase chain reaction. Levels of promotor cytokines, such as TNF alpha, TGF beta, INF gamma, and IL-2, were significantly higher in lung tissue from the bleomycin group. The expression of these cytokines in the glucocorticoid group was low, especially the peak value. Expression of IL-4 was high in the bleomycin group, and was not inhibited in the glucocorticoid group. Expression of the down-regulator cytokine IL-10 was also high in the bleomycin group and very low in the glucocorticoid group. 3. The non-selectivity of glucocorticoids with respect to promotor and suppressive cytokines may account in part for steroid resistance in bleomycin-induced pulmonary fibrosis.