PDCD1 and autoimmune hepatitis: An increase in the IL-21 expression was observed in patients with different stages of AIH, regardless of whether the patient was in remission or experiencing severe AIH, and was positively correlated with the severity of AIH.218 IL-21 is also positively correlated with the CCR6-CCL20 axis and CXCR3-CXCL9 axis and participates in the migration of immune cells expressing CXCR3 or CCR6.218 Aoki et al219 generated a lethal AIH model by removing the thymus of PD-1-deficient neonatal mice.