Am. J. Respir. Cell Mol. Biol.,
Volume 22, Number 3, March, 2000 344-351
B-Cell Epitope Mapping of DNA Topoisomerase I Defines Epitopes
Strongly Associated with Pulmonary Fibrosis in Systemic Sclerosis
Catherine
Rizou,
John P. A.
Ioannidis,
Evgenia
Panou-Pomonis,
Maria
Sakarellos-Daitsiotis,
Constantinos
Sakarellos,
Haralampos M.
Moutsopoulos,
and
Panayiotis G.
Vlachoyiannopoulos
Department of Organic Chemistry and Biochemistry, School of Natural Sciences, University of Ioannina; Clinical and
Molecular Epidemiology Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine,
Ioannina; Department of Pathophysiology, Medical School, National University of Athens, Athens, Greece;
and Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts
We hypothesized that B-cell epitope mapping of DNA Topoisomerase I (type-I topoisomerase, or Topo I)
may define epitopes strongly associated with pulmonary interstitial fibrosis (PIF) in systemic sclerosis
(SSc). B-cell epitope mapping of Topo I was performed using 63 20-mer peptides overlapping by eight residues and spanning the entire length of the Topo I sequence. These peptides, coupled to polystyrene pins,
were tested for antibody binding by enzyme-linked immunosorbent assays (ELISAs) using immunoglobulin
G fractions from anti-Topo I, anticentromere, anti-U3RNP-positive, and normal sera. Four major epitopes
were recognized by anti-Topo I sera, but not from the control sera: WWEEERYPEGIKWKFLEHKG
(205-224, epitope I), RIANFKIEPPGLFRGRGNHP (349-368, epitope II), PGHKWKEVRHDNKVTWLVSW (397-416, epitope III), and ELDGQEYVVEFDFLGKDSIR (517-536, epitope IV). Peptide-epitopes were then synthesized in their soluble forms and ELISA systems were developed. Epitopes II to IV
are localized at highly exposed sites of the Topo I tertiary structure, whereas epitope I is localized at a less
accessible site. In a cohort of 81 patients with SSc with clinical data on the evolution of their disease, patients with antibodies in their sera recognizing at least three of the four epitopes had 3.1 times (P = 0.02) the hazard of developing PIF compared with patients whose sera recognized no epitopes or only one or two of
the four epitopes. The discrimination was much stronger than that achieved by the simple determination of
Topo I antibodies by counterimmunoelectrophoresis and immunoblot (hazard ratio 1.7, P = 0.30) in the
same patients. B-cell epitope mapping of the anti-Topo I response has identified four major epitopes which
cumulatively show a strong association with the development of PIF in SSc.
