Evaluation of ERAP1 gene single nucleotide polymorphisms in immunomodulation of pro-inflammatory and anti-inflammatory cytokines profile in ankylosing spondylitis

Background: Ankylosing spondylitis (AS) is a prototype of chronic inflammatory arthritis termed seronegative
spondyloarthropathies that typically affects the joints. Among the non-Human leukocyte antigen (HLA) loci, the
strongest association has been observed with Endoplasmic reticulum aminopeptidase 1 (ERAP1) gene single nu-
cleotide polymorphisms (SNPs). Moreover, the effect of ERAP1 gene SNPs on the pro-inflammatory and anti-
inflammatory cytokines in AS disease has still been poorly elucidated. In this study, we aimed to determine the
association of ERAP1 gene SNPs (rs30187 and rs2287987) with AS risk as well as their effect on the mRNA
expression of pro-inflammatory and anti-inflammatory cytokines, with emphasis on the immunoregulation of the
IL-17/IL-23 pathway, in an Iranian population.
Methods: We performed Single specific primer (SSP)-PCR for genotyping of 160 AS patients and 160 healthy
controls. After isolation of peripheral blood mononuclear cells (PBMCs), total RNA of PBMCs was isolated,
complementary DNA (cDNA) was synthesized, and quantitative analyses of mRNA expression of cytokines were
performed by Real-time PCR for 40 HLA-B27 positive AS patients and 40 healthy individuals as controls.
Results: It was seen that T allele of rs30187 (OR= 1.54, 95% CI= 1.07–2.22, P= 0.017) and C allele of
rs2287987 (OR 1.50, 95% CI 1.05–2.14, P= 0.024) were associated with the risk of AS. Both of these alleles
were associated more strongly in the HLA-B27 positive AS patients. There was a significant overexpression of
mRNAs of pro-inflammatory (IL-17A, IL-17F, IL-23, TNF-α and IFN-γ), while downregulation of anti-in-
flammatory cytokines (IL-10 and TGF-β) in PBMCs from 40 HLA-B27 positive AS patients in comparison to
controls. AS patients with rs30187 SNP TT genotype expressed mRNA of IL-17A, IL-17F, and IL-23 significantly
higher than patents with CT and CC genotypes for this SNP.
Conclusions: This study represented the association of ERAP1 gene rs30187 and rs2287987 polymorphism with
the risk of AS. Additionally, it appears that rs30187 polymorphism may be involved in the immunomodulation of
the IL-17/IL-23 pathway in the AS disease.