Particular association of clinical and genetic features with autoimmunity to citrullinated α-enolase in rheumatoid arthritis.

OBJECTIVE: To confirm that the presence of anti-citrullinated α-enolase peptide 1 (anti-CEP-1) antibodies identifies a subgroup of patients with rheumatoid arthritis (RA).

METHODS: DNA and serum samples were obtained from 451 patients with RA and 279 healthy control subjects, all of whom were of Spanish ancestry. Antibodies to cyclic citrullinated peptide (CCP) and CEP-1 were measured by enzyme-linked immunosorbent assay. HLA-DRB1 and the R620W single-nucleotide polymorphism of PTPN22 were genotyped.

RESULTS: Anti-CEP-1 and anti-CCP antibodies were observed in 26.8% and 71.2% of the patients with RA, respectively. Most of the patients (86.6%) with anti-CEP-1 antibodies also had anti-CCP antibodies. Erosive arthritis, rheumatoid factor (RF) positivity, and the presence of the HLA shared epitope (especially the DRB1*04 alleles) were disproportionately associated with the group of patients with both antibodies. In addition, evidence of a significant interaction between the shared epitope and the risk allele of PTPN22 was observed only in these patients. In contrast, the association with these clinical and genetic features was weaker in patients with anti-CCP antibodies but lacking anti-CEP-1 antibodies. These results were obtained in patients in whom the prevalence of RA risk factors differed from that in other previously studied patients.

CONCLUSION: We observed that autoimmunity against citrullinated α-enolase may identify a subset of patients with a higher frequency of joint erosions and RF positivity. In addition, we confirmed the disproportionately large effect of the susceptibility alleles of HLA-DRB1 and their interaction with PTPN22 in this subset of patients. These results extend, confirm, and generalize the evidence supporting the specificity of the anti-CEP-1 antibody-positive subgroup of patients with RA among anti-CCP antibody-positive patients with RA.