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Cancer Diagnostics |
1 Department of Bacteriology and Immunology, Haartman Institute and HUSLAB, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland.
2 CellExSys, Seattle, WA.
3 Molecular Immunobiology Group and Department for Infection Biology, Hans Knöll Institute for Natural Products Research, Jena, Germany.
4 CuraGen Corporation, Branford, CT.
5 Division of Urology, Clinic of Surgery, Seinäjoki Central Hospital, Seinäjoki, Finland.
aAddress correspondence to this author at: Haartman Institute, University of Helsinki, PO Box 21, Helsinki FIN-00014, Finland. Fax 358-9-1912-6382; e-mail sakari.jokiranta{at}helsinki.fi.
Background: The BTA TRAKTM and BTA statTM tests for bladder cancer use monoclonal antibodies (mAbs) X13.2 and X52.1 to detect factor H (FH)-related material in urine. The exact ligands remain unknown.
Methods: Western blot analyses of purified FH, recombinant factor H-related protein 1 (FHR-1), and serum and urine samples were used to identify the ligands of X13.2 and X52.1. Recombinant FH constructs were used to identify the target sites of X13.2 and X52.1. To analyze whether natural ligands of FH could compete with its recognition by the capture mAb X52.1, we used surface plasmon resonance analysis. The role of the ligands of X52.1 in the BTA TRAK assay was tested with use of purified proteins and FH-depleted samples.
Results: X13.2 bound to domain 3 of FH and FH-like protein 1, whereas X52.1 bound to domain 18 of FH and to FHR-1. Using specific FH depletion from a bladder cancer patients urine and purified FH, we demonstrated that FH is the ligand recognized by the BTA TRAK test. By contrast, FHR-1 in urine reduced the FH-dependent test signal.
Conclusions: FH is a tumor marker for bladder cancer. To reveal the presence of bladder cancer, the BTA TRAK assay detects FH, whereas FHR-1 is able to partly inhibit this detection. This indicates a special mechanism for a diagnostic immunoassay based on the combined effect of simultaneous positive and negative signals in a single sample.
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