Higher levels of interleukin IL ‐17 and antigen‐specific IL ‐17 responses in pulmonary sarcoidosis patients with L öfgren's syndrome

Summary Sarcoidosis is a granulomatous disorder of unknown aetiology. The presence of Mycobacterium  tuberculosis catalase‐peroxidase ( mKatG ) in sarcoidosis tissue has been reported. T helper type 1 (Th1) responses against mKatG have previously been observed. However, little is known about interleukin ( IL) ‐17 and Th 17 responses in sarcoidosis. Here, we investigated the levels of IL ‐17 and frequencies of IL ‐17‐producing cells responding to mKatG in sarcoidosis patients with different prognosis. Peripheral blood and bronchoalveolar lavage ( BAL ) cells were obtained from sarcoidosis patients with or without L öfgren's syndrome (often associated with spontaneous recovery), and also stratified according to human leucocyte antigen ( HLA) type. Cells producing IL ‐17 and interferon ( IFN)‐ γ after stimulation with mKatG were enumerated by enzyme‐linked immunospot ( ELISPOT) . The level of IL ‐17 in the BAL fluid of sarcoidosis patients and healthy controls was measured by quantitative immuno‐polymerase chain reaction (q IPCR) . We also performed flow cytometry and immunohistochemistry for further characterization of IL ‐17 expression. Patients with L öfgren's syndrome had a higher frequency of IL ‐17‐producing cells responding to mKatG in BAL fluid compared to patients without L öfgren's syndrome ( P  < 0·05). The HLA ‐ DR 3 + sarcoidosis patients with L öfgren's syndrome (known to have a particularly good prognosis) also had a clearly higher level of IL ‐17 in BAL fluid compared to healthy controls and sarcoidosis patients without L öfgren's syndrome ( P  < 0·01) and ( P  < 0·05), respectively. No such difference between patient groups was observed with regard to IFN‐ γ and not with regard to either cytokine in peripheral blood. These findings suggest that IL ‐17‐producing cells may be a useful biomarker for the prognosis of sarcoidosis and play a role in the spontaneous recovery typical of patients with L öfgren's syndrome.