Different properties of ACPA and IgM-RF derived from a large dataset: further evidence of two distinct autoantibody systems.
BACKGROUND
The aim of this study was to examine seroconversion and the relationship with age and inflammation of autoantibodies in a large group of patients attending an outpatient rheumatology clinic.


METHODS
Levels of antibodies to citrullinated proteins/peptides (ACPAs) and IgM rheumatoid factor (IgM-RF) were determined in 22,427 samples collected from 18,658 patients. The diagnosis was derived from a diagnosis registration system. The degree of seroconversion in repeated samples and the correlation of levels with age and inflammatory markers were determined for ACPA and IgM-RF in rheumatoid arthritis (RA) and non-RA patients.


RESULTS
Seventy-one percent of RA patients (n = 1,524) were ACPA-positive and 53% were IgM-RF-positive; in non-RA patients (n = 2,245), the corresponding values were 2% and 4%, respectively. In patients with at least two samples (n = 3,769), ACPA status was more stable than IgM-RF status in RA patients. ACPA- or IgM-RF-negative non-RA patients seldom became positive. ACPA positivity was unrelated to age in both RA and non-RA patients. IgM-RF positivity was unrelated to age in RA patients; however, it increased with age in non-RA patients. The correlation between autoantibody levels and inflammatory markers was low in general and was somewhat higher for IgM-RF than for ACPA.


CONCLUSIONS
ACPA status is more stable in time and with increasing age than IgM-RF status, further establishing its role as a disease-specific marker. ACPA and IgM-RF levels are only moderately correlated with markers of inflammation.
Ursum
Jennie
J
Jan van Breemen Institute, 1056 AB Amsterdam, The Netherlands. j.ursum@janvanbreemen.nl
Bos
Wouter H
WH
van de Stadt
Rob J
RJ
Dijkmans
Ben A C
BA
van Schaardenburg
Dirkjan
D
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D001323:Autoantibodies / Q000096:biosynthesis / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D002956:Citrulline / Q000097:blood* / Q000276:immunology; D016208:Databases, Factual; D005260:Female; D006801:Humans; D007075:Immunoglobulin M / Q000096:biosynthesis / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012217:Rheumatoid Factor / Q000096:biosynthesis / Q000097:blood*
D001323:Autoantibodies; D015415:Biomarkers; D007075:Immunoglobulin M; D002956:Citrulline; D012217:Rheumatoid Factor