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

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.