IL-35 or Interleukin 35 is a cytokine belonging to the IL12 family, that is produced by regulatory T cells. It is a dimeric protein composed of IL-12-alpha and IL-27-beta chains. Members of this class of cytokines are important in influencing T helper cell differentiation and supressing inflammatory response. IL-35 is known to play an essential role in immune regulation of the CD4+CD25+ regulatory T (Treg) cells, from which IL-35 is also specifically produced. IL-35 is able to expand CD4+CD25+ Treg cells whereas it can inhibit proliferation of CD4+CD25- effector T (Teff) cells and development of proinflammatory Th17 cells, suppressing inflammatory responses.Synonyms: CLMF p35, Cytotoxic lymphocyte maturation factor 35 kDa subunit, IL-12 subunit p35, IL-12A, NK cell stimulatory factor chain 1, NKSF1