Associations of HLA-DRB1 alleles with anti-citrullinated protein antibody-positive and anti-citrullinated protein antibody-negative rheumatoid arthritis in northern east part of Turkey

Association of HLA-DRB1 amino acid residues with giant cell arteritis: genetic association study, meta-analysis and geo-epidemiological investigation

INTRODUCTION

Giant cell arteritis (GCA) is an autoimmune disease commonest in Northern Europe and Scandinavia. Previous studies report various associations with HLA-DRB1*04 and HLA-DRB1*01; HLA-DRB1 alleles show a gradient in population prevalence within Europe. Our aims were (1) to determine which amino acid residues within HLA-DRB1 best explained HLA-DRB1 allele susceptibility and protective effects in GCA, seen in UK data combined in meta-analysis with previously published data, and (2) to determine whether the incidence of GCA in different countries is associated with the population prevalence of the HLA-DRB1 alleles that we identified in our meta-analysis.

METHODS

GCA patients from the UK GCA Consortium were genotyped by using single-strand oligonucleotide polymerization, allele-specific polymerase chain reaction, and direct sequencing. Meta-analysis was used to compare and combine our results with published data, and public databases were used to identify amino acid residues that may explain observed susceptibility/protective effects. Finally, we determined the relationship of HLA-DRB1*04 population carrier frequency and latitude to GCA incidence reported in different countries.

RESULTS

In our UK data (225 cases and 1378 controls), HLA-DRB1*04 carriage was associated with GCA susceptibility (odds ratio (OR) = 2.69, P = 1.5×10(-11)), but HLA-DRB1*01 was protective (adjusted OR = 0.55, P = 0.0046). In meta-analysis combined with 14 published studies (an additional 691 cases and 4038 controls), protective effects were seen from HLA-DR2, which comprises HLA-DRB1*15 and HLA-DRB1*16 (OR = 0.65, P = 8.2×10(-6)) and possibly from HLA-DRB1*01 (OR = 0.73, P = 0.037). GCA incidence (n = 17 countries) was associated with population HLA-DRB1*04 allele frequency (P = 0.008; adjusted R(2) = 0.51 on univariable analysis, adjusted R(2) = 0.62 after also including latitude); latitude also made an independent contribution.

CONCLUSIONS

We confirm that HLA-DRB1*04 is a GCA susceptibility allele. The susceptibility data are best explained by amino acid risk residues V, H, and H at positions 11, 13, and 33, contrary to previous suggestions of amino acids in the second hypervariable region. Worldwide, GCA incidence was independently associated both with population frequency of HLA-DRB1*04 and with latitude itself. We conclude that variation in population HLA-DRB1*04 frequency may partly explain variations in GCA incidence and that HLA-DRB1*04 may warrant investigation as a potential prognostic or predictive biomarker.

Serum anticyclic citrullinated protein antibody titers are correlated with the response to biological agents in patients with rheumatoid arthritis

Anticyclic citrullinated protein antibody (ACPA) is known as an important indicator for diagnosis of rheumatoid arthritis (RA). Our aim was to examine the relationship between the serum ACPA titer at baseline and responsiveness to biological agents (antagonists of either tumor necrosis factor or interleukin 6) in patients with RA. ACPA was measured using second-generation chemiluminescent enzyme immunoassay. Disease activity was assessed using disease activity scores 28. Fifty-seven RA patients with biological agents were enrolled, and the median ACPA titer at baseline was 110.0 U/mL. The median ACPA titer was 23.3 U/mL and 183.0 U/mL in the good and moderate response groups, respectively, which were significantly lower than in the no response group (404.0 U/mL). In addition, 69.2% and 26.9% of patients with low (<100 U/mL) and moderate (100–499 U/mL) basal ACPA titers showed a moderate to good response. Of the patients with higher (≥500 U/mL) basal ACPA titers, only 14.0% and 42.5% showed a good or moderate response, respectively. The remission rate was 77.8% in the ACPA-negative, which was significantly higher than the rate of 25% in the ACPA-positive patients. The results suggest that the ACPA titers are correlated with the efficacy of the biological agents used in patients with RA.