Interleukin 27 (IL-27), a member of the IL-12 family, is a heterodimeric protein consisting of two subunits, Epstein-Barr virus (EBV)-inducible gene 3 (EBI3, also known as IL-27B) and IL-27p28 (known as IL-30).IL-27 is produced by antigen-presenting cells and plays an important role in regulating the activity of B and T lymphocytes. IL-27 exerts its effects by interacting with a specific cell surface receptor complex composed of two proteins, IL-27R and gp130.IL-27 has proinflammatory and anti-inflammatory properties. In response to infection, IL-27 induces the secretion of proinflammatory cytokines by monocytes and mast cells, which induce the proliferation of naïve CD4+ T cells and elicit a Th1 cell response.IL-27 also promotes the effector functions of NK cells and CD8+ T cells. As an anti-inflammatory immunomodulator, IL-27 inhibits Th1 or Th2 responses and limits the intensity and duration of adaptive immune responses. Recent studies have shown that IL-27 has good antitumor activity, and IL-27 has been reported to be actively involved in the induction of inflammation in rheumatoid arthritis.