th9 cells as a new player in inflammatory skin disorders

Cd4+t cells are composed of different subpopulations that differ in developmental pathways, surface markers, and their products. among the catalog of these cells is th9 cell subset that has a great capacity of interleukin (il)-9 production. they could be involved in the pathogenic or protective immune responses. therefore, it is important to know how th9 cells and cytokines influence the function of the human immune system as multitasking machinery, both in isolation or after the interaction with other surrounding cells. since an important characteristic of th9 cells is their tropism for skin, this article reviews the physiological and pathophysiological functions of th9 and its cytokines under normal conditions and inflammatory skin disorders.