Time-resolved fluorescence in immunocytochemical detection of prostate-specific antigen in prostatic tissue sections

Chelates with fluorescent lanthanides such as europium and terbium are widely used in immunofluorometric assays, e.g. for the measurement of different molecular forms of prostate-specific antigen (PSA) in serum for detection and monitoring of prostate cancer. These chelates have also been introduced as non-radioactive labels in immunocytochemistry and in situ hybridization. In the present study, sections of non-malignant prostate were investigated using monoclonal IgGs against PSA. Detection of specific immunostaining employing time-resolved fluorescence with europium-labeled streptavidin was compared with conventional detection by streptavidin conjugated to horse-radish peroxidase. The high PSA concentration in the tissue produced high intensity, specific time-resolved fluorescence signals in the epithelial cells of the prostate gland without disturbance from non-specific tissue autofluorescense. This allowed short exposure times to be used which resulted in insignificant photobleaching. Two of the three europium-chelates evaluated yielded high signal intensities. Counterstaining was found to be optimal with Gill No. 1-Haematoxylin solution and Merckoglas(TM) was the best mounting medium for the europium chelates tested. In conclusion, time-resolved fluorescence imaging is an attractive alternative to conventional detection of streptavidin conjugated to horse-radish peroxidase, as it provides linear, high intensity, specific signals subsequent to the decay of non-specific tissue autofluorescence.