The same ELA class II risk factors confer equine insect bite hypersensitivity in two distinct populations

Abstract

Insect bite hypersensitivity (IBH) is a chronic allergic dermatitis common in horses. Affected horses mainly react against antigens present in the saliva from the biting midges, Culicoides ssp, and occasionally black flies, Simulium ssp. Because of this insect dependency, the disease is clearly seasonal and prevalence varies between geographical locations. For two distinct horse breeds, we genotyped four microsatellite markers positioned within the MHC class II region and sequenced the highly polymorphic exons two from DRA and DRB3, respectively. Initially, 94 IBH-affected and 93 unaffected Swedish born Icelandic horses were tested for genetic association. These horses had previously been genotyped on the Illumina Equine SNP50 BeadChip, which made it possible to ensure that our study did not suffer from the effects of stratification. The second population consisted of 106 unaffected and 80 IBH-affected Exmoor ponies. We show that variants in the MHC class II region are associated with disease susceptibility (praw = 2.34 × 10−5), with the same allele (COR112:274) associated in two separate populations. In addition, we combined microsatellite and sequencing data in order to investigate the pattern of homozygosity and show that homozygosity across the entire MHC class II region is associated with a higher risk of developing IBH (p = 0.0013). To our knowledge this is the first time in any atopic dermatitis suffering species, including man, where the same risk allele has been identified in two distinct populations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00251-011-0573-1) contains supplementary material, which is available to authorized users.

Genetics of equine insect bite hypersensitivity and genetic diversity in horses

“…A same microsatellite marker was significantly associated with IBH susceptibility in Swedish-born Icelandic horses and Exmoor ponies (Andersson et al, 2012b). Also, Eqca-DRB3 gene in MHC class II region was associated with IBH susceptibility in Swedish-born Icelandic horses (Andersson et al, 2012b). Similarly, Eqca-DRA gene in MHC class II region showed significant association with IBH in Icelandic horses in Switzerland that were imported from Iceland .…”

“…IBH susceptibility has been associated to MHC class II region in different serological and candidate gene studies Andersson et al, 2012b;Marti et al, 1992). A same microsatellite marker was significantly associated with IBH susceptibility in Swedish-born Icelandic horses and Exmoor ponies (Andersson et al, 2012b). Also, Eqca-DRB3 gene in MHC class II region was associated with IBH susceptibility in Swedish-born Icelandic horses (Andersson et al, 2012b).…”

“…In horses, the MHC region has been associated with allergic disorders such as recurrent airway obstruction (RAO) susceptibility (Curik et al, 2003) and IBH susceptibility. IBH susceptibility has been associated to MHC class II region in different serological and candidate gene studies Andersson et al, 2012b;Marti et al, 1992). A same microsatellite marker was significantly associated with IBH susceptibility in Swedish-born Icelandic horses and Exmoor ponies (Andersson et al, 2012b).…”

“…Knowledge regarding IBH prevalence in Exmoor pony population is limited. However, IBH has been observed as a significant problem in this pony population (Andersson et al, 2012b;ExmoorPonySociety).…”

“…The genetic component influencing the susceptibility has also been estimated. Further, immunity related genes located at MHC region and other regions have also been associated with IBH susceptibility in various candidate gene studies Vychodilova et al, 2013;Andersson et al, 2012b). In candidate gene studies, the genes to be studies are included based on the previous knowledge of association of IBH like trait in other species for example humans.…”