Role of DLA-DRB1 amino acids outside the shared epitope in dachshund susceptibility to immune-mediated polyarthritis

Canine immune-mediated polyarthritis (IMPA) is an idiopathic disorder encompassing both erosive and non-erosive forms of rheumatoid arthritis (RA), with a clinical picture similar to human RA. Resemblance in major histocompatibility complex (MHC)-associated risk between the two was first noted within the specific amino acid motif known as the shared epitope (SE) on human leukocyte antigen DRB1. Following further identification of amino acids conferring risk for human RA outside the SE, this study was designed to examine amino acids both within and outside the classic SE in dachshunds, a breed with reported susceptibility to IMPA in Japan. Genome-wide association studies have linked positions 11, 13 and 71 with strong risk for human RA and important roles in antigen presentation to T cells. Sequence based genotyping of 16 case and 64 control dachshunds revealed strong associations comparable to human RA between IMPA risk and valine at position 11 (Val-11), phenylalanine at 13 (Phe-13), and arginine at 71 (Arg-71) on the dog leukocyte antigen (DLA)-DRB1 molecule (OR 2.89, 95%CI 1.3-6.4, p = 0.009), while association with the classic SE was significant only regarding homozygote frequency of the QRRAA haplotype-also carrying Val 11 and Phe 13 outside the SE (p = 0.04). Moreover, limited range in possible combinations of amino acids at positions 11, 13 and 71 starting with Val-11 among all DLA-DRB1 alleles registered with the GenBank and IPD-MHC canine databases, suggested potential of further single-breed analyses in dachshunds to clarify the disorder in terms of diagnosis, treatment, and epigenetic control, while clinical and immunopathogenetic similarities between human and dachshund RA also suggested the possibility of gaining insight into RA per se through study of canine IMPA as a spontaneous model of human RA.