Characterization of the immunoglobulin repertoire of the spiny dogfish (Squalus acanthias)

► We characterize the immunoglobulin repertoire of spiny dogfish. ► Ig isotypes and isoforms are highly conserved across the cartilaginous fish. ► Spiny dogfish serum IgNAR is found in a previously unknown multimeric format. ► Spiny dogfish and nurse shark express an isoform of IgW lacking a variable domain. The cartilaginous fish (chimeras, sharks, skates and rays) are the oldest group relative to mammals in which an adaptive immune system founded upon immunoglobulins has been found. In this manuscript we characterize the immunoglobulins of the spiny dogfish (Squalus acanthias) at both the molecular and expressed protein levels. Despite the presence of hundreds of IgM clusters in this species the serum levels of this isotype are comparatively low. However, analysis of cDNA sequences and serum protein suggests microheterogeneity in the IgM heavy chains and supports the proposal that different clusters are preferentially used in the two forms (monomer or pentamer) of this isotype. We also found that the IgNAR isotype in this species exists in a previously unknown multimeric format in serum. Finally, we identified a new form of the IgW isotype (the shark IgD orthologue), in which the leader is spliced directly to the first constant domain, resulting in a molecule lacking an antigen-binding domain.