IL-35 was discovered almost simultaneously by Niedbala and Collison . It was initially named at the 13th International Congress of Immunology. The structure of IL-35 is unique within the IL-12 family, as it is formed by the combination of the p35 and Ebi3 subunits connected by a disulfide bond . Other members of the IL-12 family, such as IL-12, IL-23, and IL-27, are also heterodimeric glycoproteins formed with different combinations of α and β chains .
IL-35 is primarily produced by regulatory T cells (Tregs) and has been shown to be essential for maximizing the inhibitory role of Tregs . Recent studies suggest that regulatory B cells (Bregs) also produce IL-35, and recombinant IL-35 (rIL-35) fusion proteins can induce Bregs to secrete IL-10 and IL-35 . IL-35 plays a crucial role in immune regulation by inhibiting the function of effector T cells and promoting the generation of regulatory T and B cells .
The immunosuppressive properties of IL-35 make it a promising candidate for therapeutic applications in various diseases. IL-35 has been shown to play a role in the development of autoimmune diseases and cancer . It is overexpressed in a variety of cancers and may exert its function both on antitumor immune responses and directly on tumor cells . As such, IL-35 is rapidly emerging as a promising biomarker and an attractive target for cancer therapy .