Received on August 27, 2004
Accepted on March 1, 2005

Cancer Diagnostics

Complement Factor H as a Marker for Detection of Bladder Cancer

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

^* To whom correspondence should be addressed. E-mail: sakari.jokiranta{at}helsinki.fi.

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 and to identify the target sites of X13.2 and X52.1 by use of recombinant FH constructs. To analyze whether natural ligands of FH could compete with its recognition by the capturing 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 patient's 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.