EBI3 is a subunit in two distinct heterodimeric cytokines: interleukin-27 (IL-27) and IL-35 (1-3). Like interleukin-23 (IL-23), IL-27 is a recently discovered member of the IL-6/IL-12 family of proinflammatory and immunoregulatory cytokines.  It exists as a heterodimer composed of the p40-related protein EBI3 and an IL-12 p35-related protein termed p28.  IL-27 is produced after activation by antigen-presenting cells and induces proliferation of nave but not memory CD4+ T-cells.  It acts by binding to its receptor WSX-1 (also known as TCCR) and gp130 which results in the activation of a Jak/STAT signaling cascade, suggesting the IL-27 is involved in the regulation of immune processes.  It has been suggested that IL-27 can also be used as a therapeutic agent against cancer as it can also induce tumor-specific anti-tumor activity mediated through CD8+ T-cells, IFN-gamma, and T-bet.  IL-35 is composed of EBI3 and the p35 subunit of IL-12 and has been reported to have therapeutic effects against collagen-induced arthritis by expanding the population of regulatory T cells and suppressing Th17 cells.  At least two isoform of EBI3 are known to exist.