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.