Serological epitope profile of anti-Ro52–positive patients with systemic autoimmune rheumatic diseases

Abstract

BackgroundRo52 is an interferon-inducible protein of the tripartite motif family. Antibodies against Ro52 have been described in patients with different autoimmune diseases, such as systemic lupus erythematosus and Sjögren’s syndrome, that are often associated with anti-Ro60 antibodies. The Ro52 autoantigen is extraordinarily immunogenic, and its autoantibodies are directed against both linear and conformational epitopes. The aim of this study was to evaluate the prevalence of antibodies to the five Ro52 domains, as well as to Ro52 176– to 196–amino acid (aa) and 200–239-aa peptides, in different systemic autoimmune rheumatic diseases (SARDs). We also aimed to verify whether antibodies to a single domain or domain association could increase their diagnostic specificity for any SARD.MethodsSerum samples were obtained from 100 anti-Ro52 antibody–positive patients with SARDs and from 68 controls (50 healthy donors and 18 patients with other autoimmune or allergic diseases). A special line immunoassay was created containing a full-length Ro52 antigen expressed in insect cells using the baculovirus system, five recombinant Ro52 antigen fragments [Ro52-1, Ro52-2, Ro52-3, Ro52-4 (partly overlapping Ro52-1 and Ro52-2), and Ro52-5 (partly overlapping Ro52-2 and Ro52-3)], and two Ro52 peptides (176–196 aa and 200–239 aa), all expressed in Escherichia coli.ResultsIn patients with SARDs, fragment prevalence rates were as follows: Ro52-1 = 3 %, Ro52-2 = 97 %, Ro52-3 = 0 %, Ro52-4 = 9 %, Ro52-5 = 28 %, Ro52 175–196-aa peptide = 6 %, and Ro52 200–239-aa peptide = 74 %. All control samples were negative for the full-length Ro52 and for the five fragments tested.ConclusionsThe main epitope of the Ro52 antigen was localized on fragment 2 (aa 125–267), and the majority (97 %) of SARD sera had antibodies that target this fragment. As most of the samples were positive for fragment 2 and only some for fragments 4 or 5, which partially overlap fragment 2, it seems that the target epitope is localized in the middle of fragment 2 or in the area between fragments 4 and 5. No antibody against a single epitope or a combination of epitopes was linked to any of the single SARDs.

Induction of autoimmune response to the extracellular loop of the HERG channel pore induces QTc prolongation in guinea‐pigs

“…; Infantino et al . ). Notably, the C‐terminal B30.2 domain contains the amino acid sequence (amino acids 302–321) that overlaps with HERG.…”

“…; Infantino et al . ), others did not confirm these findings, demonstrating a prevalent reactivity towards sequences included in the N‐terminal (RING‐B‐box domain) and C‐terminal parts (B30.2. domain) of the antigen (Fritsch et al .…”

“…Hennig et al (2008) found that in patients with Sjogren's syndrome, a native autoantigenic epitope is located in the zinc-binding region of the RING-B-box domain. Other studies reported a significant immunogenicity also in the B30.2 domain able to generate high antibody titres in patients with autoimmune diseases, particularly when affected by Sjögren's syndrome (Bozic et al 1993;Burbelo et al 2010;Infantino et al 2015). Notably, the C-terminal B30.2 domain contains the amino acid sequence (amino acids 302-321) that overlaps with HERG.…”

“…In fact, although some groups identified the central part of the antigen (i.e. the coiled-coil domain), particularly the p200 peptide (amino acids 200-239), as the main immunogenic region (Bozic et al 1993;Salomonsson et al 2002;Strandberg et al 2008;Burbelo et al 2010;Infantino et al 2015), others did not confirm these findings, demonstrating a prevalent reactivity towards sequences included in the N-terminal (RING-B-box domain) and C-terminal parts (B30.2. domain) of the antigen (Fritsch et al 2006).…”

Unexpected Cause of Rhabdomyolysis and Proximal Muscle Weakness

“…Due to the patient's prior diagnoses of NHL and ITP, and the presence of anti‐SSA/Ro antibody, a working diagnosis of PM seemed initially plausible. Anti‐SSA/Ro antibodies are known to be found in several conditions, including patients with systemic lupus erythematosus, subacute cutaneous lupus erythematosus, inflammatory myositis, and autoimmune hepatitis . This is especially true for antibodies against the Ro52, as opposed to the Ro60 fraction of anti‐SSA/Ro.…”