We previously reported that alveolar lymphocytes in patients with active sarcoidosis are sensitized to Propionibacterium acnes (P. acnes) which may play a significant role in the induction of alveolitis in these patients. However, the mechanism of lymphocyte activation is not fully understood. In this study, we further investigated the production of Interleukin-2 (IL-2), and the responsiveness to IL-2 of alveolar lymphocytes obtained from sarcoidosis patients and stimulated by P. acnes in vitro. In 21 untreated sarcoidosis patients, 7 treated patients and 13 control subjects, the mean IL-2 activity of fluid released from cultured alveolar lymphocytes was 9.8 +/- 15.7 u/ml (M +/- SD), 1.9 +/- 4.7 u/ml and 0.2 +/- 0.8 u/ml respectively. The IL-2 activity of lymphocytes from untreated patients was significantly higher than that of control subjects (p less than 0.02). The responsiveness of alveolar lymphocytes to recombinant IL-2 was evaluated by 3H-thymidine uptake in the presence and absence of P. acnes. Lymphocytes stimulated by P. acnes showed a significantly increased uptake (3766 +/- 3929 dpm) compared to unstimulated lymphocytes (1123 +/- 968 dpm) obtained from 11 untreated sarcoidosis patients (p less than 0.02). On the other hand, the responsiveness of lymphocytes obtained from 6 control subjects was low, regardless of stimulation by P. acnes. There was a significant correlation (p less than 0.05) between the P. acnes-induced production of IL-2 by alveolar lymphocytes and the blastogenesis of alveolar lymphocytes in untreated sarcoidosis patients. Our data indicate that P. acnes stimulates IL-2 production and IL-2 receptor induction in alveolar lymphocytes from patients with active sarcoidosis.