The dominant MHC class I locus of the duck (Anas platyrhynchos ) is adjacent to the polymorphic TAP2 locus

We examined the expression and linkage of the major histocompatibility complex (MHC) class I genes and the transporter associated with antigen processing 2 (TAP2) gene in the duck (Anas platyrhynchos). Southern blot analysis and amplification of genomic sequences suggest that ducks have at least four genes encoding MHC class 1. We constructed and screened a primary cDNA library and identified four transcripts, with overwhelming expression of one. To investigate whether this was due to linkage of the dominant MHC class I locus with TAP2, we cloned the TAP2 cDNA. Amplification of the genomic region between TAP2 and class I by PCR showed the dominantly expressed MHC class I locus is tightly linked to TAP2. TAP2 is also polymorphic and amino acid differences between the TAP2 alleles may have functional consequences for what antigenic peptide can be transported and presented. The organization of the duck MHC may have functional consequences for their ability to eliminate viral pathogens.