Background/Purpose:

Anti-nuclear antibodies (ANA) are present in approximately 90% of sera from systemic sclerosis (SSc) patients and play an important role in the diagnosis and prognosis of SSc. Recently, a novel autoantibody targeting the Cytoskeleton-Like Bicaudal D Protein Homolog 2 (BICD2) has been described in SSc. Studies to date on BICD2 show a significant overlap with anti-centromere antibodies. We aimed to analyze the B-cell epitopes of anti-BICD2 antibodies and to study the clinical associations of this antibody in SSc.

Methods:

Serum pools with (n=2) and without (n=1) anti-BICD2 antibodies, assayed by an addressable laser bead-based immunoassay (ALBIA) with recombinant BICD2, were used for epitope discovery with peptide arrays covering the full-length amino acid sequences of CENP-A, CENP-B and BICD2. The identified candidate sequences were then utilized to synthesize synthetic, biotinylated, soluble peptides for ALBIA. The peptides were tested on five groups of patients [BICD2(+)/CENP-A(+) (n=15), BICD2(-)/CENP-A(+) (n=10), BICD2(+)/CENP-A(-) (n=5), BICD2(-)/CENP-A(-) (n=10), and healthy individuals (n=7)]. A total of 451 well characterized SSc patients were used to establish sero-clinical associations.

Results:

Epitope mapping revealed a serine/proline-rich nonapeptide SPSPGSSLP comprising amino acids 606–614 localized to a non-coiled coil domain of BICD2 as the core epitope. This epitope had 29.6% identity and 55.6% similarity to a peptide in CENP-A (TGTPGPSRRGP) within which PGPSRR was previously identified as a key CENP-A epitope. Among the five groups of patients tested for reactivity with the BICD2 derived epitope, the highest reactivity was observed in BICD2(+)/CENP-A(+) sera followed by the BICD2(-)/CENP-A(+) group. In the BICD2(+)/CENP-A(-) group, one patient showed moderate reactivity. No reactivity was observed in the BICD2(-)/CENP-A(-) group or in HI. Next, we compared the reactivity to recombinant BICD2 (aa 606-821) with the BICD2 and the CENP-A derived peptides using spearman correlation. We observed a significant correlation between antibodies to the BICD2 and the CENP-A derived peptide (r=0.70; p<0.0001), to a lesser extent between CENP-A peptide and recombinant BICD2 (r=0.42; p<0.0001) and between recombinant BICD2 and the BICD2 peptide (r=0.59; p<0.0001). Inhibition experiments demonstrated that the anti-CENP-A peptide reactivity could be abolished with the BICD2 derived peptide and vice versa. However, some sera also had reactivity to the recombinant BICD2 protein that could not be inhibited by CENP-A peptide, indicating that there might be additional BICD2 specific epitopes. Anti-BICD2 antibody positive SSc patients (without other SSc specific antibodies) showed significantly higher prevalence of myositis (p=0.003) and less bacterial overgrowth (p=0.043). Conclusion:

In the present study, we first describe a linear B-cell epitope on BICD2 which shows sequence homology and cross-reactivity with an epitope on CENP-A, which explains the strong serological overlap between anti-BICD2 and anti-centromere antibodies. Anti-BICD2 antibodies may have additional diagnostic and prognostic properties beyond currently known SSc-specific antibodies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/identification-of-a-sub-population-of-autoantibodies-targeting-bicd2-cross-reacting-with-cenp-a-derived-peptides-in-patients-with-systemic-sclerosis/