Major Histocompatibility Complex class IIB polymorphism in an ancient Spanish breed.

Genes from the Major Histocompatibility Complex class II region are involved in the presentation of antigens. Therefore, they have the key role in regulating the immune response and in the resistance to infections. We investigated the Major Histocompatibility Complex class IIB genes, DRB and DQB, in Churra sheep, one of the most important indigenous breeds of Spain. These genes are among the most polymorphic in the mammalian genome. Furthermore, often different numbers of class IIB genes per haplotype exist, complicating the genotyping and sequencing of these genes. Especially the DQB region is only partially characterized in sheep and the repertoire of DRB and DQB alleles in Churra sheep, an ancient breed, is unknown. Here, we sequenced the class IIB genes for 15 rams that are the pedigree heads of a selection Nucleus herd. In total, we found 12 DRB and 25 DQB alleles. From these, 3 and 15 were new, respectively. Fourteen haplotypes carrying one or two DQB alleles could be deduced and the evolutionary relationship of these was investigated by phylogenetic trees. Based on the sequences of these most common class II alleles, a more efficient genotyping system for larger numbers of Churra sheep will be developed.