IL-27, a heterodimer protein, belongs to the IL-12 cytokine family. IL-27 is composed of the Epstein-Barr virus-induced gene 3 (EBI-3), a 34 kD glycoprotein that is related to the p40 subunit of IL-12; and p28, a 28 kD glycoprotein that is related to the p35 subunit of IL-12 and p19 subunit of IL-23. IL-27 triggers expansion of antigen-specific na?ve CD4+ T cells, promotes polarization of Th1 cells, and inhibits the development of Th2 and Th17 cells. It is known that IL-27 is an early product of activated antigen-presenting cells (APCs). IL-27 plays an important role in regulating the activity of B and T lymphocytes.