Identifying and quantifying apoptosis: navigating technical pitfalls

Apoptosis or programmed cell death is often altered in malignancies and is frequently determined by the terminal transferase-mediated nick end labeling technique (TUNEL). However, commercially available protocols can produce high background and false-positive staining, which renders the distinction between apoptosis and necrosis difficult. In an attempt to develop a rapid and reproducible method for detecting and quantifying apoptosis, we coupled optimization of the Apoptag Plus Peroxidase In Situ Apoptosis Detection kit with quantitative histomorphometric computer imaging software using the Bacus Laboratories Incorporated Slide Scanner (BLISS). Multiple (200-350) unique 40x images were scanned using the BLISS system and downloaded into the WebSlide Browser program, creating a permanent, scanned record of the area assessed. The stored images were counted, with the final analysis simultaneously taking into account cells that were immunohistochemically positive and the histology of the surrounding cells to reduce the possibility of false positive and negative staining. In addition, cells with equivocal staining can be simultaneously reviewed by other technologists with networked WebSlide Browser access to the same images. Our data show that the advantages offered by the BLISS imaging software greatly reduce the potential drawbacks of using the TUNEL method as a sole means of quantification.