Anti-PAD4 autoantibodies in rheumatoid arthritis: levels in serum over time and impact on PAD4 activity as measured with a small synthetic substrate.
Isoform 4 of the human peptidylarginine deiminase (hPAD4) enzyme may be responsible for the citrullination of antigens in rheumatoid arthritis (RA) and has been shown to be itself the target of disease-specific autoantibodies. Here, we have tested whether the level of serum anti-hPAD4 antibodies in RA patients is stable over a period of 10 years and whether the antibodies influence hPAD4-mediated deimination of the small substrate N-α-benzoyl-L-arginine ethyl ester. RA sera (n = 128) obtained at baseline and after 10 years were assessed for anti-hPAD4 antibodies by a specific immunoassay. For 118 RA patients, serum anti-hPAD4 IgG levels were stable over 10 years. Seven patients who were negative for anti-PAD4 IgG at baseline had become positive after 10 years. Further, total IgG from selected RA patients and controls were purified, and a fraction was depleted for anti-hPAD4 antibodies. Kinetic deimination assays were performed with total IgG and depleted fractions. The k ( cat ) and K ( m ) values of hPAD4-mediated deimination of N-α-benzoyl-L-arginine ethyl ester were not affected by the depletion of the anti-hPAD4 antibodies from the total IgG pool. In conclusion, RA patients remain positive for anti-hPAD4 antibodies over time and some patients who are initially anti-hPAD4 negative become positive later in the disease course. The anti-hPAD4 antibodies did not affect the enzymatic activity of hPAD4 when the small substrate N-α-benzoyl-L-arginine ethyl ester was used. However, this finding may not exclude an effect of these autoantibodies on citrullination of protein substrates in RA.
Centre for Immune Regulation, Institute of Immunology, University of Oslo, Oslo University Hospital-Rikshospitalet, 0027 Oslo, Norway.
Sylvie
S
Pollmann
Maria
M
Stensland
Eirik Hornes
EH
Halvorsen
Ludvig M
LM
Sollid
Tore K
TK
Kvien
Burkhard
B
Fleckenstein
Oyvind
O
Molberg
D001120:Arginine / Q000031:analogs & derivatives* / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000201:enzymology / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D002384:Catalysis; D018450:Disease Progression; D006801:Humans; D006867:Hydrolases / Q000097:blood / Q000276:immunology*; D007118:Immunoassay; D007074:Immunoglobulin G / Q000097:blood*; D007700:Kinetics; D009664:Norway; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases; D012720:Severity of Illness Index; D013379:Substrate Specificity
D001323:Autoantibodies; D015415:Biomarkers; D007074:Immunoglobulin G; D001120:Arginine; C009727:benzoylarginine ethyl ester; D006867:Hydrolases; C000629235:PADI4 protein, human; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases
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