Rheumatoid arthritis-specific autoantibodies to peptidyl arginine deiminase type 4 inhibit citrullination of fibrinogen.
OBJECTIVE
Autoantibodies to citrullinated proteins are specific for rheumatoid arthritis (RA) and recognize epitopes centered by citrulline, a posttranslationally modified form of arginine. Peptidyl arginine deiminase type 4 (PAD-4), the enzyme that converts arginine into citrulline, is in itself a target for RA-specific autoantibodies. This study was undertaken to assess whether anti-PAD-4 autoantibodies interfere with citrullination in vitro in patients with RA, and to identify peptide targets of anti-PAD-4 antibodies that can activate or inhibit citrullination.


METHODS
To test whether autoantibodies to PAD-4 influence citrullination, an in-house citrullination assay was developed using purified autoantibodies to PAD-4. To map B cell epitopes on PAD-4, 65 overlapping 20-mer peptides encompassing the entire PAD-4 were analyzed for their reactivity in RA sera.


RESULTS
Autoantibodies to PAD-4 inhibited PAD-4-mediated citrullination. Three linear peptides on PAD-4 were recognized almost uniquely by PAD-4 autoantibodies in the sera of patients with RA. One peptide was located in the N-terminal, calcium-binding domain of PAD-4, while 2 other peptides were located in the C-terminal, substrate-binding domain of PAD-4.


CONCLUSIONS
Autoantibodies to PAD-4 inhibit in vitro citrullination of fibrinogen by PAD-4. Most anti-PAD-4-positive sera recognize peptides located both in the N-terminal domain (211-290) and the C-terminal domain (601-650) of PAD-4.
Auger
Isabelle
I
INSERM Unité 639, Marseilles, France. isabelle.auger@inserm.fr
Martin
Marielle
M
Balandraud
Nathalie
N
Roudier
Jean
J
D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D002956:Citrulline / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D018604:Epitope Mapping; D018985:Epitopes, B-Lymphocyte / Q000737:chemistry / Q000276:immunology; D005340:Fibrinogen / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D006867:Hydrolases / Q000737:chemistry / Q000276:immunology*; D010455:Peptides / Q000737:chemistry / Q000276:immunology; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases
D001323:Autoantibodies; D018985:Epitopes, B-Lymphocyte; D010455:Peptides; D002956:Citrulline; D005340:Fibrinogen; D006867:Hydrolases; C000629235:PADI4 protein, human; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases