**2.3 IL-17 family**

IL-17 is a pro-inflammatory cytokine. There are six family known members of IL-17. Also, we have just a little information of its biological functions, being the IL-17A and the IL-17F described recently [18]. IL-17–related cytokines play key roles in defense against extracellular pathogen, and their participation in the development of autoimmune diseases has drawn significant attention. Moreover, some of these molecules are involved in the amplification and perpetuation of pathological processes in many inflammatory diseases. However, the same cytokines can exert anti-inflammatory effects in specific settings, as well as play a key role in the control of immune homeostasis [19, 20].
