Evolutionarily conserved IL-20 enhances the response of JAK1/STAT3 axis in Carassius cuvieri × Carassius auratus red var

The IL-20 cytokine family, which includes only IL-20, IL-22 and IL-26 in teleost, has a wide range of biological functions and is essential for epithelial integrity and innate host defense. IL-22 and IL-26 are the most intensively studied cytokine within this family; however, the immunological function of IL-20 in fish is essentially unknown. In this study, we examined the expression and function of an IL-20 homologue (WR-IL20) from White crucian carp (Carassius cuvieri, WCC, female) × Red crucian carp (Carassius auratus red var., RCC, male). WR-IL20 and its parents, WCC-IL20 and RCC-IL20, were both composed of 177 residues with high identities among them. Additionally, gene structure, functional domain, tertiary structure, multiple sequence alignment, and phylogeny analysis showed a conserved status between WR-IL20, WCC-IL20 and RCC-IL20. WR-IL20, WCC-IL20 and RCC-IL20 were mainly expressed in the head kidney and were upregulated by Aeromonas hydrophila infection in vivo. Furthermore, recombinant WR-IL20 protein (rWR-IL20) induced increased transcript levels of c-Myc, cyclin D, Bcl-2, JAK1, TYK2 and STAT3 in head kidney lymphocytes in vitro. These results provide a new perspective for understanding the origin, evolution and function of IL-20 in teleost.