Abstract

Gamma interferon (IFN gamma) is a potent immune mediator that plays a central role in enhancing cellular immune processes. This study demonstrates that while lung mononuclear cells from normal individuals spontaneously release little or no interferon (less than 10 U/10(6) cells per 24 h), those from patients with pulmonary sarcoidosis spontaneously release considerable amounts (65 +/- 20 U/10(6) cells per 24 h, P less than 0.02 compared to normals). Furthermore, cells from patients with active disease release far more interferon than those from patients with inactive disease (101 +/- 36 compared to 24 +/- 8 U/10(6) cells per 24 h, P less than 0.02). Characterization of this interferon using acid sensitivity, specific antibody inhibition, and target cell specificity criteria demonstrated that it was almost entirely IFN gamma. This spontaneous release of IFN gamma appeared to be compartmentalized to the lung of these patients in that their blood mononuclear cells spontaneously released little or no IFN gamma (P less than 0.02, compared to sarcoidosis lung mononuclear cells) and no IFN gamma was detected in their serum. Both lung T lymphocytes and alveolar macrophages contributed to the spontaneous release of IFN gamma by lung mononuclear cells from sarcoid patients; purified preparations of T lymphocytes and alveolar macrophages from these patients spontaneously released similar amounts of IFN gamma (56 +/- 21 and 32 +/- 11 U/10(6) cells per 24 h, respectively, P greater than 0.3). At least one role for IFN gamma in the pathogenesis of sarcoidosis appeared to be related to activation of alveolar macrophages, as alveolar macrophages recovered from patients with active disease spontaneously killed [3H]uridine-labeled tumor cell targets (17.7 +/- 4.5% cytotoxicity compared with 2.8 +/- 0.9% in normals, P less than 0.02) and purified IFN gamma enhanced the ability of alveolar macrophages from sarcoidosis patients with inactive disease to kill similar targets (P less than 0.001, compared to alveolar macrophages cultured in medium alone). Treatment of sarcoid patients with corticosteroids, a therapy known to suppress the activity of the disease, caused a marked reduction in the level of spontaneous IFN gamma release by lung mononuclear cells compared with untreated patients (P less than 0.02), which suggests that the effectiveness of corticosteroid therapy in controlling active pulmonary sarcoidosis may, at least in part, be due to suppression of IFN gamma release.