| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Letters |
1
Dept. of Pathol. & Lab. Med., Mount Sinai Hosp., 600 University Ave., Toronto, Ontario, M5G 1X5 Canada,
2
Dept. of Lab. Med. and Pathobiol., Univ. of Toronto, Toronto, Ontario, M5G 1L5 Canada
a Author for correspondence. Fax (416) 586-8628; e-mail ediamandis{at}mtsinai.on.ca.
To the Editor:
Prostate-specific antigen (PSA) is a tumor marker widely used for the diagnosis and management of patients with prostate cancer. Despite the original notion that PSA was a prostatic tissue-specific marker, it is now well accepted that PSA can be found in many nonprostatic tissues and fluids (1). With the advent of highly sensitive methods for measuring trace amounts of PSA, it became possible to show that female sera demonstrate PSA immunoreactivity (2)(3)(4). If PSA immunoassays with detection limits of ~1 ng/L are used, then ~50% of female sera are positive for PSA. However, because of very low concentrations of PSA in female serum, it is impossible to characterize the immunoreactivity in detail and prove that it indeed represents PSA and not immunoassay noise (cross-reactivity or nonspecific effects) (5). Here, we describe a method that demonstrates that the immunoreactivity in female serum is not due to nonspecific effects of the immunoassay used.
We first developed a method that is capable of recognizing
purified seminal plasma PSA down to 0.25 ng/L. This assay is
essentially identical to the one described by us previously
(6), but we replaced the final time-resolved
fluorometric measurement of alkaline phosphatase with a
chemiluminescence detection method using the substrate
CDP-StarTM from Tropix, Inc. Substrate incubation was for
15 min at room temperature. The monoclonal antibodies used in this
assay are the same as in our previous assays (6). This PSA
assay uses a mouse monoclonal capture antibody encoded 8301 and a
biotinylated mouse monoclonal detection antibody encoded 8311 (both
from Diagnostic Systems Laboratories). For nonspecificity studies, we
used another mouse monoclonal antibody— against
-fetoprotein (AFP)—from the same manufacturer.
The detection limit of this assay, defined as the concentration of PSA that corresponds to the signal of the zero calibrator plus 2 SD, was 0.25 ng/L. Currently, no commercial assay measures PSA concentrations <10 ng/L.
To study whether the PSA immunoreactivity in female serum is indeed specific, we followed this method. We selected 12 female sera that were tested by the PSA assay reported previously (6) and had immunoreactivity of 0–550 ng/L. We then prepared two 400-µL aliquots per sample. To the first aliquot we added 1 µL (1 µg) of the 8301 PSA antibody, and to the second aliquot we added 1 µL (1 µg) of the AFP antibody. We then incubated both aliquots for 4 h at room temperature. All aliquots were assayed in triplicate, and PSA concentrations were determined from the calibration curve (data not shown).
Table 1
summarizes the PSA concentrations in antibody-supplemented
female sera. Clearly, PSA immunoreactivity was detected in all sera
supplemented with the AFP antibody (control), but it essentially
disappeared when the sera were supplemented with the 8301 antibody,
which is identical to theimmobilized capture antibody.
Immunoreactive amounts of unsup-plemented sera were identical
to the concentrations in the sera to which the anti-AFP antibody was
added (data not shown). These data support the view that the measured
immunoreactivity is PSA specific, because the matrices of the two
aliquots of each sample were essentially identical and contained the
same amounts of the added mouse monoclonal antibodies. The PSA
immunoreactivity from the one aliquot disappeared because it reacted
with the 8301 antibody and thus became incapable of binding to the same
antibody in the solid phase.
|
These data support the view that PSA is a normal constituent of female serum. Possible diagnostic applications of PSA measurements in female serum have been proposed recently (7)(8)(9)(10).
References
The following articles in journals at HighWire Press have cited this article:
|
|
 |
|
  E. Elkord, P. E. Williams, H. Kynaston, and A. W. Rowbottom Differential CTLs specific for prostate-specific antigen in healthy donors and patients with prostate cancer Int. Immunol., October 1, 2005; 17(10): 1315 - 1325. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. H. Black, M. Giai, R. Ponzone, P. Sismondi, H. Yu, and E. P. Diamandis Serum Total and Free Prostate-specific Antigen for Breast Cancer Diagnosis in Women Clin. Cancer Res., February 1, 2000; 6(2): 467 - 473. [Abstract] [Full Text]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
