IDO1 and psoriasis: To investigate the association of IDO1 and IDO2 with psoriasis, we immunohistologically evaluated the normal skin samples of healthy volunteers (n = 7), and the lesional and non-lesional skin samples of patients with psoriasis (n = 8), using antibodies against IDO1 and IDO2. All skin samples, of both patients with psoriasis and healthy volunteers, were negative for IDO1 in the epidermis (Figure 1a).