Thymus cDNA library survey uncovers novel features of immune molecules in Chinese giant salamander Andrias davidianus

•A thymus cDNA library of Chinese giant salamander was constructed and screened.•Compared with known amphibian homologs, IgD has fewer constant domains but contains a hinge region.•A novel IgY lacking an Fc region was identified from Chinese giant salamander.•A previously undescribed amphibian IFI6 occurs in two different forms in this species.•Andrias davidianus TCR beta is the most abundant gene and displays a polyclonal repertoire.

A ranavirus-induced thymus cDNA library was constructed from Chinese giant salamander, the largest extant amphibian species. Among the 137 putative immune-related genes derived from this library, these molecules received particular focus: immunoglobulin heavy chains (IgM, IgD, and IgY), IFN-inducible protein 6 (IFI6), and T cell receptor beta chain (TCRβ). Several unusual features were uncovered: IgD displays a structure pattern distinct from those described for other amphibians by having only four constant domains plus a hinge region. A unique IgY form (IgY(ΔFc)), previously undescribed in amphibians, is present in serum. Alternative splicing is observed to generate IgH diversification. IFI6 is newly-identified in amphibians, which occurs in two forms divergent in subcelluar distribution and antiviral activity. TCRβ immunoscope profile follows the typical vertebrate pattern, implying a polyclonal T cell repertoire. Collectively, the pioneering survey of ranavirus-induced thymus cDNA library from Chinese giant salamander reveals immune components and characteristics in this primitive amphibian.