IL17RA and ankylosing spondylitis: The IL-17RA pathway may be activated by gut microbiota (Figure 4F), and is related to most autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis (AS), and inflammatory bowel disease (Atarashi et al., 2015; Kim et al., 2016).