Antibodies to citrullinated alpha-enolase peptide 1 are specific for rheumatoid arthritis and cross-react with bacterial enolase.
OBJECTIVE
To map the antibody response to human citrullinated alpha-enolase, a candidate autoantigen in rheumatoid arthritis (RA), and to examine cross-reactivity with bacterial enolase.


METHODS
Serum samples obtained from patients with RA, disease control subjects, and healthy control subjects were tested by enzyme-linked immunosorbent assay (ELISA) for reactivity with citrullinated alpha-enolase peptides. Antibodies specific for the immunodominant epitope were raised in rabbits or were purified from RA sera. Cross-reactivity with other citrullinated epitopes was investigated by inhibition ELISAs, and cross-reactivity with bacterial enolase was investigated by immunoblotting.


RESULTS
An immunodominant peptide, citrullinated alpha-enolase peptide 1, was identified. Antibodies to this epitope were observed in 37-62% of sera obtained from patients with RA, 3% of sera obtained from disease control subjects, and 2% of sera obtained from healthy control subjects. Binding was inhibited with homologous peptide but not with the arginine-containing control peptide or with 4 citrullinated peptides from elsewhere on the molecule, indicating that antibody binding was dependent on both citrulline and flanking amino acids. The immunodominant peptide showed 82% homology with enolase from Porphyromonas gingivalis, and the levels of antibodies to citrullinated alpha-enolase peptide 1 correlated with the levels of antibodies to the bacterial peptide (r2=0.803, P<0.0001). Affinity-purified antibodies to the human peptide cross-reacted with citrullinated recombinant P gingivalis enolase.


CONCLUSIONS
We have identified an immunodominant epitope in citrullinated alpha-enolase, to which antibodies are specific for RA. Our data on sequence similarity and cross-reactivity with bacterial enolase may indicate a role for bacterial infection, particularly with P gingivalis, in priming autoimmunity in a subset of patients with RA.
Lundberg
Karin
K
Kennedy Institute of Rheumatology, Imperial College London, London, UK. k.lundberg@imperial.ac.uk
Kinloch
Andrew
A
Fisher
Benjamin A
BA
Wegner
Natalia
N
Wait
Robin
R
Charles
Peter
P
Mikuls
Ted R
TR
Venables
Patrick J
PJ
D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000382:microbiology*; D001323:Autoantibodies / Q000276:immunology*; D001426:Bacterial Proteins / Q000276:immunology*; D016866:Bacteroidaceae Infections / Q000276:immunology*; D014408:Biomarkers, Tumor / Q000737:chemistry / Q000276:immunology*; D016022:Case-Control Studies; D002956:Citrulline / Q000737:chemistry / Q000276:immunology; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000276:immunology*; D018604:Epitope Mapping; D005260:Female; D006801:Humans; D008297:Male; D010751:Phosphopyruvate Hydratase / Q000737:chemistry / Q000276:immunology*; D016966:Porphyromonas gingivalis / Q000201:enzymology / Q000276:immunology*; D025521:Tumor Suppressor Proteins / Q000737:chemistry / Q000276:immunology*
D001323:Autoantibodies; D001426:Bacterial Proteins; D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D002956:Citrulline; C095157:ENO1 protein, human; D010751:Phosphopyruvate Hydratase