Role of interleukin-2 in the development and persistence of lymphocytic alveolitis in farmer's lung.

Farmer's lung (FL) is characterized by an intense lymphocytic alveolitis which persists after an acute episode with continuous exposure to the offending antigens. This study aimed to examine the role of interleukin-2 (IL-2) in the development and persistence of this lymphocytic alveolitis. Three groups of dairy farmers were studied: acute FL, ex-FL (past history of FL but no clinical evidence of active disease) and asymptomatic farmers (no lung disease). IL-2 was measured by enzyme immunosorbent assay and T-cell proliferation was evaluated by 3H-thymidine incorporation. Acute and ex-FL patients had more lymphocytes (p<0.01) and higher levels of IL-2 (p<0.05) in their bronchoalveolar lavage (BAL) than asymptomatic farmers. BAL T-lymphocytes from acute and ex-FL patients released considerable amounts of IL-2 after stimulation with concanavalin A and showed dose-dependent proliferative responses to IL-2. IL-2 production was decreased after treatment with prednisone. Acute FL patients, but not ex-FL, had higher levels of soluble CD25 in their serum than asymptomatics (p=0.009). These results suggest that interleukin-2 may play a role in farmer's lung by providing a stimulus not only for the accumulation of lymphocytes but also for their persistence at the site of hypersensitivity reaction, and that the lung is a likely source of this cytokine in vivo.