IDO-expressing DCs and Foxp3+ Tregs have been implicated in the development of various infectious and autoimmune pathological conditions of the epithelium, including lichen planus, lupus vulgaris, sarcoidosis and infections caused by Mycobacterium leprae, Haemophilus ducreyi, UPEC and Leishmania sp. Here, IDO1 is linked to sarcoidosis.