The MHC of the duck (Anas platyrhynchos) contains five differentially expressed class I genes

J Immunol. 2005 Nov 15;175(10):6702-12. doi: 10.4049/jimmunol.175.10.6702.


MHC class I proteins mediate a variety of functions in antiviral defense. In humans and mice, three MHC class I loci each contribute one or two alleles and each can present a wide variety of peptide Ags. In contrast, many lower vertebrates appear to use a single MHC class I locus. Previously we showed that a single locus was predominantly expressed in the mallard duck (Anas platyrhynchos) and that locus was adjacent to the polymorphic transporter for the Ag-processing (TAP2) gene. Characterization of a genomic clone from the same duck now allows us to compare genes to account for their differential expression. The clone carried five MHC class I genes and the TAP genes in the following gene order: TAP1, TAP2, UAA, UBA, UCA, UDA, and UEA. We designated the predominantly expressed gene UAA. Transcripts corresponding to the UDA locus were expressed at a low level. No transcripts were found for three loci, UBA, UCA, and UEA. UBA had a deletion within the promoter sequences. UCA carried a stop codon in-frame. UEA did not have a polyadenylation signal sequence. All sequences differed primarily in peptide-binding pockets and otherwise had the hallmarks of classical MHC class I alleles. Despite the presence of additional genes in the genome, the duck expresses predominantly one MHC class I gene. The limitation to one expressed MHC class I gene may have functional consequences for the ability of ducks to eliminate viral pathogens, such as influenza.

Publication types

  • Comparative Study

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Chickens
  • Conserved Sequence
  • DNA, Complementary / genetics
  • Ducks / genetics*
  • Ducks / immunology*
  • Evolution, Molecular
  • Gene Duplication
  • Gene Expression
  • Genes, MHC Class I*
  • Genetic Variation
  • Histocompatibility Antigens Class I / genetics
  • Humans
  • Mice
  • Molecular Sequence Data
  • Phylogeny
  • Promoter Regions, Genetic
  • Sequence Homology, Amino Acid
  • Sequence Homology, Nucleic Acid
  • Species Specificity


  • DNA, Complementary
  • Histocompatibility Antigens Class I