Classical crosses of common carp (Cyprinus carpio L.) show co-segregation of antibody response with major histocompatibility class II B genes

In cyprinids, two paralogous groups of major histocompatibility (MH) class II B genes, DAB1 and DAB3, have been reported but have not been studied in detail. In our study on MH association with immune responsiveness in common carp (Cyprinus carpio L.) we have taken a long-term approach using divergent selection for antibody production. We report the co-segregation of Cyca-DAB1-like and Cyca-DAB3-like genes with antibody response, in backcrosses to high- and low-responsive parental carp lines. We show that the presence of Cyca-DAB1-like, but not Cyca-DAB3-like genes, preferentially leads to a high DNP-specific antibody response in carp. Background genes other than Cyca-DAB genes also influenced the level of antibody response. Our data support the hypothesis of a genetic control by Cyca-DAB genes on the antibody response measured. We could not detect an association of the Cyca-DAB genes with disease resistance to the parasite Trypanoplasma borreli. Sequence information, constitutive transcription levels and our co-segregation data indicate that both paralogous Cyca-DAB1-like and Cyca-DAB3-like groups represent functional MH class II B genes. Previously defined differences in allelic diversity between Cyca-DAB1-like genes, especially, identify Cyca-DAB1 as the most interesting DAB gene for further study in common carp.