IL17A and ankylosing spondylitis: Type 3 innate lymphoid cells (ILC3) differentiate in the intestine and migrate to extraintestinal sites, especially recirculating between the intestine and bone marrow (BM), and are involved in the development of ankylosing spondylitis (AS) through the production of IL-17 and IL-22, which may be responsible for the induction of inflammation (27).