IL17A and viral infectious disease: MAIT cells can be considered to span both the innate and adaptive arms, and play an important role in the innate host defense against various bacterial and viral infections (e.g., influenza virus, hepatitis B virus, hepatitis C virus, hepatitis D virus, as well as human immunodeficiency virus type 1), through secreting effector molecules, including interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), Granzyme B, perforin, and interleukin 17 (IL-17) (17, 21–24).