Genomic organization of the chicken CD8 locus reveals a novel family of immunoreceptor genes

The genomic organization of the chicken CD8alpha gene was investigated to determine the basis of its polymorphism. Contiguous to the CD8alpha gene we identified multiple DNA blocks possessing sequences homologous to CD8alpha. Gene conversions and recombination over evolutionary time among CD8alpha and these CD8alpha homologous genes seem to account for the observed polymorphism. Furthermore, these CD8alpha-like DNAs encode a distinct multigene family of immunoreceptors that have a charged or polar residue in place of the interspecies-conserved CD8alpha transmembrane proline residue and a short cytoplasmic tail nonhomologous to CD8alpha. The identification of this novel multigene family with an organization reminiscent of human killer Ig-like receptors raises compelling questions on their evolutionary relationship among immunoreceptors.