IL17A and immune system disorder: Interleukin-17 (IL-17) and interleukin-22 (IL-22) act as effector cytokines of the T-helper 17 (Th-17) cells [132,163], which play a crucial part to maintain the chronic and relapsing phase of multiple immune diseases that include DED and SS, and were increased in DED patients compared to normal subjects [164].