IL-27, a member of the IL-12 family, is a heterodimeric protein consisting of the p40-related protein Epstein-Barr virus-induced gene 3 (EBI3) non-covalently linked to an IL-12p35-related protein, p28 (also known as IL-30). IL-27 plays an important function in regulating the activity of B- and T-lymphocytes. The effects of IL-27 are eliciting by its interaction with a specific cell-surface receptor complex composed of two proteins known as IL27R and gp130. Recent studies indicate that IL-27 has potent anti-tumor activity. It has been reported that IL-27 is critically involved in the induction of inflammation in rheumatoid arthritis.