IL22 and polycystic ovary syndrome: Rising pieces of evidence suggest the correlation between gut microbiota and PCOS (8, 9); our studies demonstrated that the gut microbiota–bile acid–IL-22 axis is involved in PCOS development via the crosstalk of gut innate immune system and ovary function (9, 10), providing strong evidence for the contribution of the gut microbiota in PCOS pathogenesis, while other possible pathways involved in gut microbiota need to be further explored.