[3][4][5] IL-26 is the most recently identified member of the IL-20 cytokine subfamily,[6] which was formed according to the usage of common receptor subunits and similarities in target-cell profiles and functions.

[7] 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.

[11] IL-26 is a 171-amino acid protein that exhibits six alpha helices connected by loops and four conserved cysteine residues.

[4] Originally named AK155, IL-26 was categorized in the IL-10 cytokine family due to sequence homology and secondary structure similarities.

[16] Pathologically, fibroblasts harvested from the inflamed synovia of patients with rheumatoid arthritis constituted the main source of IL-26.

Ligand binding by functional IL-26 receptor complex results in the initiation of a signal transduction pathway involving receptor-associated Janus tyrosine kinases Jak1 and Tyk2.

Interleukin 26 (IL-26) is an inflammatory mediator and a driver of chronic inflammation due to its ability to act as a carrier of extracellular DNA,[22] and as an antimicrobial molecule through its capacity to form pores in bacterial membranes.

IL-26 is a natural human antimicrobial that promotes immune sensing of bacterial and host cell death.

[26] A novel effect of IL-26 produced by donor-derived CD26+ CD4+ T cells on the pathophysiology of pulmonary chronic GVHD was observed in a murine model.

By contrast to other IL-10 cytokine family members, no induction of primary human keratinocyte proliferation in response to IL-26 has been detected.