HLA-DRB1*0404 is strongly associated with anticalpastatin antibodies in rheumatoid arthritis.
OBJECTIVE
To test whether HLA-DR alleles influence the production of particular autoantibodies in rheumatoid arthritis (RA) patients, we screened synovial proteins with sera of RA patients homozygous for different HLA-DR alleles by using 2D blots. We found that sera of RA patients homozygous for HLA-DRB1*0404 recognised a 100-kDa synovial protein identified as calpastatin. We studied B and T cell epitopes on calpastatin and their association with HLA-DRB1*0404.


METHODS
The frequency of positive sera in patients expressing different RA-associated HLA-DR allele combinations was calculated by inhouse ELISA using purified synovial calpastatin or calpastatin peptides encompassing the entire calpastatin protein as immunosorbent. Interaction between calpastatin peptides and HLA-DR alleles was tested by a direct binding assay. T cell responses to calpastatin were measured in RA patients and controls.


RESULTS
We found that RA-associated HLA-DR alleles are associated with presence of autoantibodies to synovial calpastatin in RA patients' sera. HLA-DRB1*0404 is strongly associated with antisynovial calpastatin in RA sera. One linear B cell epitope is preferentially associated with HLA-DRB1*0404. Multiple peptides from calpastatin bind every tested HLA-DR allele associated or not with RA. Peptides from domain 1 and 4 of calpastatin are the best HLA-DR allele binders. The T cell response to calpastatin is frequent in RA patients and independent of the HLA-DR background.


CONCLUSIONS
HLA-DRB1*0404 is strongly associated with anticalpastatin antibodies in rheumatoid arthritis.
Auger
Isabelle
I
INSERM UMR 639, Faculté de Médecine, 27 BD Jean Moulin, 13005 Marseille, France. isabelle.auger@medecine.univ-mrs.fr
Roudier
Chantal
C
Guis
Sandrine
S
Balandraud
Nathalie
N
Roudier
Jean
J
D000483:Alleles; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001323:Autoantibodies / Q000032:analysis* / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology; D002135:Calcium-Binding Proteins / Q000276:immunology* / Q000494:pharmacology; D016022:Case-Control Studies; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D016009:Chi-Square Distribution; D015180:Electrophoresis, Gel, Two-Dimensional; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes; D020022:Genetic Predisposition to Disease; D006684:HLA-DR Antigens / Q000032:analysis* / Q000378:metabolism; D059811:HLA-DRB1 Chains; D006801:Humans; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013583:Synovial Membrane / Q000276:immunology*; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology
D001323:Autoantibodies; D002135:Calcium-Binding Proteins; D000939:Epitopes; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; C033668:calpastatin