Autoantibodies against topoisomerase I detected with the natural enzyme and overlapping recombinant peptides.

Antibodies against topoisomerase I (anti-topo I, anti-Scl-70) are regarded as a marker of systemic sclerosis. The various frequencies of anti-topo I detected in those patients depends at least in part on the test design and the kind of the antigen used. We therefore analyzed three overlapping recombinant topo I fragments (N-terminal, center and C-terminal part of the molecule) covering the full length of the enzyme for substitution of highly purified natural antigens (n-topo I) in ELISA for antibody screening. 49 of 50 sera reacting with n-topo I in ELISA also recognized the recombinant C-terminal topo I fragment under identical test conditions, 37 sera recognized the recombinant center and two sera the recombinant N-terminal peptide. All sera reactive with the N-terminal and center peptide reacted with the recombinant C-terminus which therefore may substitute for the natural antigen. In immunoblot assays 92% (46/50) of the sera reacted with n-topo I and 86% (43/50) with the recombinant C-terminal peptide. Immunoblots therefore seem to be less sensitive for detecting anti-topo I antibodies than ELISA regardless the source of the antigen used. In a screening of 696 sera submitted for routine antibody tests the recombinant peptide ELISA on the other hand detected two sera which did not react with n-topo I in ELISA. Because of the high rate of agreement within the results obtained with the two antigens, n-topo I can be substituted by the recombinant peptide ELISA allowing better standardization and interlaboratory comparison of results.