MHC class II DRB1 and DQA2 gene polymorphisms in four indigenous breeds of sheep (Ovis aries)

Documentation of extensive genetic diversity in the Ovar-DRB1 gene in native Turkish sheep

Indigenous breeds have a high level of genetic diversity that might contribute to develop animal breeds with desired traits such as disease resistance and high productivity. Major histocompatibility complex (MHC) is a key component of adaptive immune system and consists of highly polymorphic genes that take part in adaptive immune response and disease resistance. Exploring and understanding the effect of polymorphisms in MHC could be beneficial to future animal breeding strategies. In this study, we sequenced the highly polymorphic Exon2 of the ovine DRB1 gene using Sanger sequencing to explore the diversity of this gene in six indigenous Turkish sheep breeds and two crossbreeds. In total, 894 haplotypes from 447 sheep were investigated, and 69 different haplotypes including 27 novel ones were identified. Among the identified haplotypes there were common and breed specific haplotypes. There was a relatively high diversity of the alleles within indigenous breeds. Allelic diversity patterns were mostly associated with geographical differences. The results of this study highlight the genetic variation within indigenous breeds which has important implications for biodiversity and the adaptability of breeds to specific environments. There is value to further studies which include other genomic regions and traits, and these could guide breeding strategies.

Characterisation of major histocompatibility complex class IIa haplotypes in an island sheep population

The ovine MHC class IIa is known to consist of six to eight loci located in close proximity on chromosome 20, forming haplotypes that are typically inherited without recombination. Here, we characterise the class IIa haplotypes within the Soay sheep (Ovis aries) on St. Kilda to assess the diversity present within this unmanaged island population. We used a stepwise sequence-based genotyping strategy to identify alleles at seven polymorphic MHC class IIa loci in a sample of 118 Soay sheep from four cohorts spanning 15 years of the long-term study on St. Kilda. DRB1, the most polymorphic MHC class II locus, was characterised first in all 118 sheep and identified six alleles. Using DRB1 homozygous animals, the DQA (DQA1, DQA2 and DQA2-like) and DQB (DQB1, DQB2 and DQB2-like) loci were sequenced, revealing eight haplotypes. Both DQ1/DQ2 and DQ2/DQ2-like haplotype configurations were identified and a single haplotype carrying three DQB alleles. A test sample of 94 further individuals typed at the DRB1 and DQA loci found no exceptions to the eight identified haplotypes and a haplotype homozygosity of 21.3%. We found evidence of historic positive selection at DRB1, DQA and DQB. The limited variation at MHC class IIa loci in Soay sheep enabled haplotype characterisation but showed that no single locus could capture the full extent of the expressed variation in the region.

Antibody responses to chimeric peptides derived from parasite antigens in mice and other animal species

Peptide vaccines constitute an interesting alternative to classical vaccines due to the possibility of selecting specific epitopes, easy of production and safety. However, an inadequate design may render these peptides poorly immunogenic or lead to undesirable outcomes (e.g., formation of B neoepitopes). As an approach to vaccine development, we evaluated the antibody response to chimeras composed of two or three known B epitopes from Trichinella and Fasciola, and several linkers (GSGSG, GPGPG and KK) in species as different as mice, sheep and turbot. All these species could mount an effective immune response to the short chimeric peptides. Nevertheless, this response depended on several factors including a favorable orientation of B-cell epitopes, adequateness of linkers and/or probability of formation of T neoepitopes. We also observed that, at least in mice, the inclusion of a decoy epitope may have favorable consequences on the antibody response to other epitopes in the chimera.