[Sarcoidosis: immunopathology and criteria of biological activity]

In France, sarcoidosis is the most frequent interstitial lung disease of unknown origin. Its prevalence is about 9.5 in 100 000. Almost 30% of the patients require corticosteroid treatment. Although the aetiology remains unknown, detailed concepts of the immunopathogenesis have been suggested. Employing the technique of bronchoalveolar lavage, some immunopathogenic mechanisms have been elucidated and the hypothesis that an unknown causative agent stimulates T-lymphocytes and macrophages by physiological mechanisms has emerged. The activity of these cells maintains the inflammation and is the target of the corticosteroid therapy. By new serologic parameters it is possible to gauge this activity and to document the therapeutic effect.