IL-27 beta/EBI3

Interleukin-27 subunit beta, better known as Epstein-Barr virus-induced gene 3 (EBI3, IL-27B), is a 34 kDa soluble glycoprotein homologous to the p40 subunit of IL-12, originally identified as a gene strongly upregulated in B lymphocytes infected with Epstein-Barr virus. EBI3 lacks a membrane anchor and shares only 27% sequence identity with p40, yet adopts a similar soluble cytokine receptor-like fold with one Ig domain and two fibronectin type III domains. EBI3 is the shared beta subunit of three heterodimeric cytokines: IL-27 (with p28), IL-35 (with p35) and IL-39 (with p19). Through these pairings it participates in strikingly different immunology-antiviral and antitumor Th1 promotion via IL-27, Treg-mediated suppression via IL-35, and pro-inflammatory B cell activity via IL-39. EBI3 is expressed by dendritic cells, monocytes, endothelial cells and trophoblasts, is induced by RANKL in osteoclastogenesis, and is elevated in inflammatory bowel disease, rheumatoid arthritis and various carcinomas.