That peptides Ap1–17 and Ap17–30 represent the immunodominant epitopes targeted by
anti-CENP-A antibodies was confirmed by us in a series of 75 SSc patients who screened
positive for ACA on a commercially available ELISA kit: 66 (88.0%) had antibodies reacting to
Ap1–17 and 62 (82.6%) were seropositive to Ap17–30, while only three (4%) were negative for
both [116]. Because the antigen in the ELISA kit was recombinant CENP-B, which is not homologous to CENP-A, our findings show that most patients with ACA have antibodies to both
CENPs. Additionally, by receiver operating characteristic analysis in an extended number of 85
SSc patients with ACA and 65 healthy blood donors as a comparison group, we showed that the
serum titer to both peptides (chemically conjugated with glutaraldehyde) discriminated the two
groups (SSc vs. control) better than one or the other peptide alone (Fig. 1). These results indicate
that almost all ACA-positive sera react with both epitopes of CENP-A. Therefore, the conjugated
peptides can substitute the use of commercial recombinant CENP-B for diagnostic purposes (e.g.
in ELISAs).