Genetic susceptibility to sarcoid in Arabian horses: associations with MHC class II and compound MHC class I/KLRA genotypes

Although the Major Histocompatibility Complex (MHC) has been repeatedly associated with susceptibility to equine sarcoid, a disease associated with bovine papillomavirus infection, the role of the MHC in the mechanisms of the disease is not fully understood. The objectives of our work were to analyze associations between polymorphic markers of the MHC genomic subregions and of the Natural Killer Complex (NKC) genomic region and the presence of sarcoid in Arabian horses. Microsatellite loci located in the MHC class I, II and III subregions and two MHC class II genes (DRA, DQA1), along with a set of NKC (KLRA, CLEC subregions) microsatelllite markers were genotyped. Fifteen microsatellites of the standard parentage kit, located outside the MHC and NKC regions, were tested as controls. Standard chi-square and Fisher tests with Bonferroni corrections were used for association analyses. Significant associations of MHC class II and MHC class I_KLRA polymorphic markers with the presence of clinical sarcoid were observed. These findings are consistent with biological theory and indicate a role of MHC class I, class II and KLRA molecules in adaptive as well as in innate immune responses to equine sarcoid. Although limited to Arabian horses, these data point to an as yet unadressed hypothesis regarding the possible roles of NK cells in the pathogenesis of equine sarcoid.