Characterization of interleukin-20 from black carp and its role in the antiviral innate immunity.

Interleukin-20 (il20) is known to participate in inflammation and host defense in mammals, whereas its immunological role in teleost fish needs to be further explored. In this study, a black carp (Mylopharyngodon piceus) il20 homolog, designated bcil20, was cloned and characterized. The full-length coding sequence of bcil20 encodes a putative protein of 179 amino acids with a predicted signal peptide and a conserved IL-10 family domain. Phylogenetic and structural analyses indicated that bcil20 is evolutionarily conserved. Expression analysis showed that bcil20 was constitutively expressed in multiple tissues and was markedly induced by spring viremia of carp virus (SVCV) and grass carp reovirus (GCRV). Western blot analysis confirmed that bcIl20 was present in both cell lysates and culture supernatants of transfected HEK293T cells, indicating that bcil20 is a secreted cytokine. Functional assays demonstrated that both bcil20 overexpression and treatment with bcIl20-conditioned medium significantly upregulated the expression of inflammatory and antiviral genes in EPC cells. Moreover, bcil20 reduced viral replication and cytopathic effects caused by both SVCV and GCRV. Besides, extracellular bcIl20 conferred dose-dependent antiviral protection. Collectively, these findings identify bcil-20 as a virus-responsive secreted cytokine that links innate immune activation to antiviral defense in black carp, and provide new insight into the function of il20 in teleost fish.