Interleukin-26 (IL-26) is a protein that in humans is encoded by the IL26 gene.
IL-26 is a 171-amino acid protein, which is similar in amino acid sequence to interleukin 10. It was originally called AK155 and is composed of a signal sequence, 6 helices, and 4 conserved cysteine residues. IL-26 is expressed in certain herpesvirus-transformed T cells but not in primary stimulated T cells. IL-26 signals through a receptor complex comprising two distinct proteins called IL-20 receptor 1 and IL-10 receptor 2. By signaling through this receptor complex, IL-26 induces rapid phosphorylation of the transcription factors STAT1 and STAT3, which enhance IL-10 and IL-8 secretion and as expression of the CD54 molecule on the surface of epithelial cells.