AJTR Copyright © 2009-All rights reserved. Published by e-Century Publishing Corporation, Madison, WI 53711
Am J Translational Res 2010;2(2):145-155

Original Article
Extraordinary antigenicity of the human Ro52 autoantigen

Peter D. Burbelo, Kathryn H. Ching, Brian L. Han, Emily R. Bush, Westley H. Reeves, Michael J. Iadarola

Neurobiology and Pain Therapeutics Section, Laboratory of Sensory Biology, National Institute of Craniofacial
Research, National Institutes of Health, Bethesda, Maryland, U.S.A.  and Division of Rheumatology and Clinical
Immunology and Center for Autoimmune Diseases, University of Florida, Gainesville, Florida, U.S.A.

Received March 1, 2010; accepted March 12, 2010, available online March 15, 2010

Abstract: Autoantibody levels to the SSA complex, composed of Ro52 and Ro60 proteins, are commonly
measured in the diagnoses of Sjögren’s Syndrome (SjS), as well as other rheumatological diseases.  One of
these proteins, Ro52, is an interferon-inducible member of the tripartite motif family bearing a RING motif
functioning as an E3 ligase that ubiquitinates interferon regulatory factor 8 and other proteins.  Using Luciferase
Immunoprecipitation Systems (LIPS) we explored the antigenicity of Ro52 in detail.   Analysis of antibody
responses against Ro52 and 20 other established antigens revealed that Ro52 had the highest antibody titers
and most likely represents one of the most immunogenic human proteins.   While the antibody titers in many of
the SjS patients were significantly and substantially higher than the controls, all healthy individuals had anti-Ro52
autoantibodies.   N- and C-terminal fragments of Ro52 showed immunoreactivity in these serum samples, but
the sums of these antibody titers were significantly lower than the antibody titers directed against the full-length
Ro52.  Antibody profiling of controls and SjS patients with three different N-terminal fragments of Ro52 revealed
that the coiled-coil region was the most useful diagnostic (66% sensitivity), followed by the B-box (31%
sensitivity), and then the RING-finger (24% sensitivity).  The C-terminal region of Ro52, containing the B30.2
domain, showed higher antibody titers in SjS patients compared to controls and this region was responsible for
the high level of Ro52 immunoreactivity in healthy individuals.  Analysis of immunoreactivity to TRIM5, a Ro52-
related protein, and the B30.2 domain from BTN1 and pyrin, failed to show significant antibody titers with the
control or SjS patient serum.  These results highlight the unusually high level of Ro52 antigenicity and
demonstrate that autoantibodies are directed at both linear and conformational epitopes spanning the entire

Key words: Autoantibody, autoantigen, Sjögren’s Syndrome, Luciferase Immunoprecipitation Systems (LIPS),
and Ro52

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Address all correspondence to:
Peter D. Burbelo, PhD
Building 49, Room 1C36, 49 Convent Drive
Bethesda, MD 20892.  
Tel: 301-402-0778.  Fax: 301-402-0667