The urodele amphibian Pleurodeles waltl has a diverse repertoire of immunoglobulin heavy chains with polyreactive and species-specific features

• The diversity of Pleurodeles waltl IgY antibodies is equivalent to the one of mammalian IgA.
• Urodele amphibian antibodies present potential polyreactive properties.
• Some urodele IGVH genes have a stretch of three cysteine at the end of CDR1.
• A disulfide bound likely links CDR1 and CDR2 in some urodele IGHV genes.

Urodele amphibians are an interesting model because although they possess the cardinal elements of the vertebrate immune system, their immune response is apparently subdued. This phenomenon, sometimes regarded as a state of immunodeficiency, has been attributed by some authors to limited antibody diversity. We reinvestigated this issue in Pleurodeles waltl, a metamorphosing urodele, and noted that upsilon transcripts of its IgY repertoire were as diverse as alpha transcripts of the mammalian IgA repertoire. Mu transcripts encoding the IgM repertoire were less diverse, but could confer more plasticity. Both isotypes present potential polyreactive features that may confer urodele antibodies with the ability to bind to a variety of antigens. Finally, we observed additional cysteines in CDR1 and 2 of the IGHV5 and IGHV6 domains, some of which specific to urodeles, that could allow the establishment of a disulfide bond between these CDRs. Together, these data suggest that urodele antibody diversity is not as low as previously thought.