Complement factor H as a marker for detection of bladder cancer.
BACKGROUND
The BTA TRAK and BTA stat 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 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.
Cheng
Zhu-Zhu
ZZ
Department of Bacteriology and Immunology, Haartman Institute and HUSLAB, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland.
Corey
Michael J
MJ
Pärepalo
Maria
M
Majno
Sandra
S
Hellwage
Jens
J
Zipfel
Peter F
PF
Kinders
Robert J
RJ
Raitanen
Mika
M
Meri
Seppo
S
Jokiranta
T Sakari
TS
D000911:Antibodies, Monoclonal / Q000378:metabolism; D000951:Antigens, Neoplasm / Q000652:urine; D001666:Binding Sites, Antibody; D014408:Biomarkers, Tumor / Q000652:urine; D001798:Blood Proteins / Q000378:metabolism / Q000652:urine; D002295:Carcinoma, Transitional Cell / Q000175:diagnosis*; D003180:Complement C3b Inactivator Proteins; D017242:Complement Factor H / Q000276:immunology / Q000378:metabolism / Q000652:urine*; D006801:Humans; D008024:Ligands; D008297:Male; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020349:Surface Plasmon Resonance; D001749:Urinary Bladder Neoplasms / Q000175:diagnosis*
D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D001798:Blood Proteins; C493495:CFH protein, human; C517621:CFHR1 protein, human; D003180:Complement C3b Inactivator Proteins; D008024:Ligands; C112999:bladder tumor-associated antigen; C100631:factor H-related protein 1; D017242:Complement Factor H