IL17A and Behcet disease: Evidence supporting the classification of BD in the autoimmune disease group stems from the following observations: major histocompatibility complex class I (MHC-I) identification, response to immunosuppressive treatments and the presence of antigen-specific T lymphocytes, such as T-helper 17 (Th17) pathway involvement and IL-17 and IL-21 production from Th17 cells [24,26].