Cytokine are small polypeptides or glycoproteins synthesized and secreted by a variety of tissue cells, primarily immune cells. Cytokines mediate cellular interactions and have various biological functions, such as regulating cell growth, differentiation and maturation, functional maintenance, modulating immune response, participating in inflammatory response, wound healing and tumor regression, etc. There are interleukins, interferons, tumor necrosis factors, hematopoietic factors, growth factors, chemokines, etc., are collectively referred to as cytokines.