Expression of thioredoxin in granulomas of sarcoidosis: possible role in the development of T lymphocyte activation.

BACKGROUND: Activated T lymphocytes are one of the characteristic features of sarcoidosis. The mechanism of T cell activation, expressing various activation markers including interleukin 2 receptor (IL-2R), has been extensively investigated but the precise mechanism remains unknown. Although thioredoxin (TRX) displays a number of biological activities including IL-2R inducing activity, its role in the induction of IL-2R expression on T cells in sarcoidosis has not been determined. The expression of TRX and IL-2R in granulomas of patients with sarcoidosis has been studied to clarify a possible role for TRX in the induction of IL-2R expression.

METHODS: Granulomas in specimens of lung tissue and lymph nodes from five patients with sarcoidosis were immunohistochemically stained with anti-TRX antibody and anti-IL-2Ralpha chain antibody and the concentration of TRX in the bronchoalveolar lavage (BAL) fluid from 20 patients with pulmonary sarcoidosis was measured.

RESULTS: Granulomas in lung and lymph node tissue from patients with sarcoidosis showed strong reactivity with anti-TRX antibody. Positive staining was present in the macrophages, epithelioid cells, and Langhans' type giant cells but not in lymphocytes. IL-2R was expressed on lymphocytes in the same granulomas. By contrast, positive immunoreactivity was not found in lung tissue specimens from 12 control subjects. Concentrations of TRX in BAL fluid were higher in patients with pulmonary sarcoidosis (median (range) 122.6 (20.9-303.3) ng/ml) than in control subjects (32.9 (16.8-52.8) ng/ml, p<0.05).

CONCLUSIONS: TRX is highly expressed and is locally produced by granulomas in patients with sarcoidosis. The coexistence of immunoreactive TRX and IL-2R in the same granulomas suggests that TRX might act as a local inducing factor for IL-2R expression on T cells.