Th17 are a newly discovered population of T helper lymphocytes characterized by the production of IL-17 (IL-17A). Interleukin 17 activates production of cytokines which are responsible for migration of neutrophils and development of inflammatory reaction. Among the other cytokines secreted by Th17 cells are TNF-a, IL-1b, IL-6 and IL-22. Development of Th17 lymphocytes gave rise numerous researches on mechanisms leading to differentiation of CD4+ cells towards new subpopulation and enabled to define factors conditioning the line.