IL-35: a new immunomodulator in autoimmune rheumatic diseases.

IL-35 is a relatively new cytokine that emerges as an important immunomodulator. IL-35 belongs to IL-12 cytokine family that includes IL-12, IL-23, IL-27, and IL-35. These cytokines are heterodimers that share subunits and their receptors also share subunits. Whereas IL-12 and IL-23 are clearly proinflammatory cytokines, the role of IL-35 is less clear. In mice, IL-35 appears to be anti-inflammatory and to protect from autoimmune inflammatory diseases. IL-35 induces the expansion of a subset of regulatory T cells (Tregs) and Bregs and mediates their suppressive function and inhibits Th17 cells. It also upregulates osteoprotegerin and suppresses RANKL, thus inhibiting bone resorption. In autoimmune rheumatic diseases, findings are conflicting, although in systemic lupus erythematosus, there is reduced function of IL-35. In psoriatic arthritis, a disease characterized by bone erosion and bone formation in peripheral joints and bone formation in spinal joints, serum levels of IL-35 were found increased in one study. Further data are required to define the exact role of IL-35 in human autoimmune rheumatic diseases.