Session Title: B-cell Biology and Targets in Autoimmune Disease
Session Type: Abstract Submissions (ACR)
Background/Purpose: The presence of anti-citrullinated protein antibodies (ACPA) is one of the most predictive factors for the development of rheumatoid arthritis (RA). Nonetheless, relatively little information is present on the absolute concentration ACPA in serum and synovial fluid in relation to total Ig-concentrations. Here, we estimated the relatively abundance of ACPA immunoglobulins in serum and synovial fluid using a quantitative approach.
Methods: ACPA from synovial fluid and serum samples were purified using high affinity strep columns coupled with biotinylated Cyclic Citrullinated Peptide (CCP). A control column (CCP-arginine) was used to guarantee the specificity of the antibody. Total IgG, IgA, IgM and anti-CCP isotype reacitivity were measured by Enzyme-linked immunosorbent assay (ELISA).
Results: ACPA were successfully isolated as substantial amounts of antibodies were eluted from sera of ACPA positive patients and neglectable amounts of antibodies were eluted from sera of ACPA negative patients. In serum samples and synovial fluid of ACPA-positive RA patients with high ACPA-levels at least one percent of total IgG was IgG ACPA. Furthermore IgM-ACPA was most abundant in synovial fluid samples as compared to serum samples (with the highest enrichment in the range of 1 IgM ACPA for every 33 total IgM antibodies). IgA, IgG and IgM ACPA were more abundantly present in synovial fluid as compared to paired serum and plasma samples.
Conclusion: IgG-ACPA is present in high concentrations in synovial fluid and serum, as at least 1 in every 100 antibodies present are ACPA in patients with high ACPA-levels. Strikingly, IgM-ACPA is abundantly present in synovial fluid. Given the short half life of IgM, these data indicate the presence of a continuous ongoing autoimmune response in the synovial compartment that is hallmarked by the activation of IgM-ACPA producing B cells.
T. W. J. Huizinga,
R. E. M. Toes,
L. A. Trouw,
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