Molecular characterization and functional analysis of IL-19 like in large yellow croaker (Larimichthys crocea).

Interleukin-19 like (IL-19L) is a member of the interleukin-10 family and plays a crucial role in inflammation, immune regulation, and other biological processes. Although the characteristics and functions of IL-10 family members in mammals have been elucidated, those of IL-19L in fish remain poorly understood. In this study, we cloned the IL-19L gene from the large yellow croaker (Larimichthys crocea), designated as LcIL-19L. The open reading frame (ORF) of LcIL-19L comprises 684 base pairs, encoding 227 amino acids, and lacks a signal peptide. It possesses a typical IL-10 domain and six conserved cysteine residues. The predicted three-dimensional structure of LcIL-19L consists of eight α-helices and two β-sheets. Genomic synteny analysis revealed that it is adjacent to the IL-10 gene. LcIL-19L was constitutively expressed in all examined tissues and cells. In vivo experiments demonstrated that poly(I:C) stimulation and Vibrio alginolyticus infection induced the expression of LcIL-19L in the head kidney and spleen. In vitro experiments also showed that poly(I:C), lipopolysaccharide (LPS), phytohemagglutinin (PHA), and phorbol myristate acetate (PMA) promoted the expression of LcIL-19L in primary head kidney leukocytes (HKLs). The recombinant LcIL-19L (rLcIL-19L) protein was able to induce the expression of cytokines (IL-1β, IL-6, IL-8, IL-10, TNF-α1, and TGF-β1) and reduce the levels of reactive oxygen species (ROS). To our knowledge, this study is the first report on the cloning, expression, and functional characterization of fish IL-19L. In summary, LcIL-19L in fish exhibits immune-regulatory functions and may serve as a key molecule that regulates the inflammatory response, laying the foundation for further investigating the mechanisms underlying the immune-regulatory role of fish IL-19L.