Session Information
Session Type: Abstract Submissions (ACR)
Background/Purpose:
Autoantibodies targeting Ku, an abundant nuclear protein with DNA helicase activity, have been reported in patients with systemic autoimmune rheumatic diseases. Little is known about the clinical association of anti-Ku antibodies, especially when tested using novel technologies. The objective of the present study was to analyze the prevalence of anti-Ku antibodies in different pathologies using a novel chemiluminescence immunoassay (CIA) on the BIO-FLASH®, a fully random access automated immunoanalyzer.
Methods:
Serum samples from adult patients with systemic lupus erythematosus (SLE, n=305) and autoimmune myositis patients (AIM, n=109) were used. Results were compared to disease controls (rheumatoid arthritis, n=30; infectious diseases, n=17) and healthy adults (HA, n=167). In addition, samples from patients referred to a rheumatology clinic submitted for routine autoantibody testing (n=1078) were studied. All samples were tested for anti-Ku antibodies by QUANTA Flash Ku (research use only, INOVA Diagnostics, San Diego, CA, USA) using recombinant Ku coupled to paramagnetic beads. SLE patient samples were also tested for other connective tissue disease associated autoantibodies using the respective QUANTA Lite® ELISAs (INOVA Diagnostics). Clinical data of anti-Ku positive patients (high titers) from the referral study were collected by retrospective chart review. Statistical analysis (Fisher exact test, receiver operating characteristics [ROC] analysis) was done with ANALYSE-IT version 2.03.
Results:
At cut-off values of 10,000 or 15,000 relative light units (RLU), 43/305 (14.1%) or 30/305 (9.8%) SLE patients and 4/109 (3.7%) AIM patients were positive, respectively. The 4 positive AIM patients had myositis in overlap, including 2 patients with SLE and myositis. In the control cohorts, 4/167 (2.4%) or 2/167 (1.2%) HA (all low titer), respectively, 0/30 (0.0%) rheumatoid arthritis and 0/17 (0.0%) infectious disease patients were positive. The area under the curve values were: 0.65 for SLE vs. controls and 0.37 for AIM vs. controls. In three SLE patients, anti-Ku antibodies were the only detectable autoantibody. In the rheumatology clinic referral cohort, 12/1078 (1.1%) were positive for anti-Ku antibodies, 9 showing low and 3 high titers. The diagnoses of the 3 high positive anti-Ku positive patients were: suspected SLE, mixed connective tissue disease, and rheumatoid arthritis treated with anti-TNF in a patient with a positive ANA.
Conclusion:
Anti-Ku antibodies detected by CIA are present in 14.1% or 9.8% of SLE, but in only 3.7% of AIM patients, 50% of whom have SLE. This suggests that anti-Ku antibodies are associated with SLE rather than with AIM. This association may have been missed in previous studies due to the past use of indirect immunofluorescence screening assays or the high sensitivity of the current CIA assay.
Disclosure:
M. Mahler,
Inova Diagnostics, Inc.,
3;
J. Wu,
Inova Diagnostics, Inc.,
3;
M. Szmyrka-Kaczmarek,
None;
A. Swart,
None;
M. J. Fritzler,
Inova Diagnostics, Inc.,
5;
J. L. Senécal,
None;
J. G. Hanly,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/anti-ku-autoantibodies-in-systemic-lupus-erythematosus-versus-autoimmune-myositis-as-measured-by-a-novel-chemiluminescence-assay/