Interleukin 39 (IL-39) is a new member of the IL-12 family and is composed of IL-23p19 and Ebi3 subunits.The two subunits, IL-23p19 and Ebi3, are shared with IL-23 and IL-27/IL-35. IL-23p19 is a four-helix bun dle and has homology with IL-6 and granulocyte colony stimulating factor. Ebi3 was first identified in B lympho cytes infected with EB virus. Some studies have reported that The combination of IL-23R and gp130 forms the IL-39 receptor. At present, a research on IL-39 is still in its initial stage, and many issues have not been solved.