Molecular cloning, characterization and expression analysis of Tim-3 and Galectin-9 in the woodchuck model

In recent years, a critical role for T cell immunoglobulin mucin domain 3 (Tim-3) and its ligand Galectin-9 (Gal-9) has emerged in infectious disease, autoimmunity and cancer. Manipulating this immune checkpoint may have immunotherapeutic potential and could represent an alternative approach for improving immune responses to viral infections and cancer. The woodchuck (Marmot monax) infected by woodchuck hepatitis virus (WHV) represents an informative animal model to study HBV infection and HCC. In the current study, the cDNA sequences of woodchuck Tim-3 and Gal-9 were cloned, sequenced and characterized. The extracellular domain of Tim-3 cDNA sequence consisted of 576 bp coding sequence (CDS) that encoded 192 amino acids. The 1076 bp full-length Gal-9 cDNA sequence consisted of 1059 bp coding sequence (CDS) that encoded 352 amino acids with a molecular weight of 39.7 kDa. The phylogenetic tree analysis revealed that the woodchuck Tim-3 and Gal-9 had the closest genetic relationship with Ictidomys tridecemlineatus. The result of quantification PCR analysis showed that ubiquitous expression of Gal-9 but not Tim-3 in different tissues of naive woodchucks. Elevated liver Gal-9 expression was observed in woodchucks with chronic WHV infection. Moreover, a polyclonal antibody against the extracellular domain of woodchuck Tim-3 were generated and identified by flow cytometry. Our results serve as a foundation for further insight into the role of Tim-3/Galectin-9 signaling pathway in viral hepatitis and HCC in the woodchuck model.