Detection of antibodies to deiminated recombinant rat filaggrin by enzyme-linked immunosorbent assay: a highly effective test for the diagnosis of rheumatoid arthritis.
OBJECTIVE
To assay antifilaggrin autoantibodies, we developed an enzyme-linked immunosorbent assay (ELISA) using a "citrullinated" recombinant rat filaggrin. Our objectives were to assess its value for diagnosing rheumatoid arthritis (RA) and to compare the results with those obtained using 4 other reference methods for detection of antifilaggrin autoantibodies, including the commercially available ELISA that uses a modified "citrullinated" synthetic peptide derived from the sequence of human filaggrin (CCP-ELISA).


METHODS
We analyzed 711 sera from patients with well-characterized rheumatic diseases, including 240 patients with RA. Antifilaggrin autoantibodies were detected by an ELISA using a recombinant rat filaggrin deiminated in vitro as immunosorbent (ArFA-ELISA). The results considered were the differences between the optical densities obtained on deiminated and nondeiminated proteins. Antibodies to rat esophagus epithelium were detected by indirect immunofluorescence, while antibodies to human filaggrin were detected by immunoblotting and by a recently described ELISA using a deiminated recombinant human filaggrin. Finally, CCP-ELISA was performed according to the manufacturer's recommendations.


RESULTS
At the titer thresholds allowing diagnostic specificities of 0.95, 0.985, and 0.99 to be reached, the diagnostic sensitivities of the ArFA-ELISA were 0.76, 0.67, and 0.65, respectively. At these 3 thresholds, the sensitivities were significantly higher than those of the 4 other tests. Despite incomplete overlapping of the 5 tests, the high diagnostic performance of the ArFA-ELISA allows us to propose this test to replace all the other methods for antifilaggrin autoantibody detection.


CONCLUSIONS
ArFA-ELISA appears to be the most efficient test among those available for the detection of antifilaggrin autoantibodies, in terms of diagnostic accuracy for RA. Its diagnostic performance in early RA and its prognostic value are currently under evaluation.
Vincent
Christian
C
Institut National de la Santé et de la Recherche Médicale (CJF 96-02, IFR30), Purpan School of Medicine, University of Toulouse III, Toulouse, France. cviencent@cict.fr
Nogueira
Leonor
L
Sebbag
Mireille
M
Chapuy-Regaud
Sabine
S
Arnaud
Michel
M
Letourneur
Odile
O
Rolland
Dominique
D
Fournié
Bernard
B
Cantagrel
Alain
A
Jolivet
Michel
M
Serre
Guy
G
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000175:diagnosis / Q000276:immunology; D001323:Autoantibodies / Q000097:blood*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D004817:Epidermis / Q000276:immunology; D005260:Female; D000091344:Filaggrin Proteins; D006801:Humans; D007381:Intermediate Filament Proteins / Q000097:blood* / Q000276:immunology; D007633:Keratins / Q000276:immunology; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000097:blood / Q000276:immunology; D012680:Sensitivity and Specificity
D001323:Autoantibodies; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D007381:Intermediate Filament Proteins; D011994:Recombinant Proteins; D007633:Keratins