Improved detection of apoptotic cells using a modified in situ TUNEL technique.

We are in the process of assessing the response of cancer tissues to chemotherapy, evaluating, among other points, the proportion of cancer cells undergoing apoptosis. However, the apoptotic index obtained with the original TUNEL technique was lower than that obtained by evaluation of apoptosis on H&E-stained sections. Here we describe a small modification of the TUNEL technique that significantly increases the sensitivity of the assay. In the nonmodified TUNEL technique, a digoxigenin-labeled probe is detected using a direct peroxidase-conjugated system, whereas here we report the advantage of using a streptavidin-biotin-immunoperoxidase system. This, in conjunction with pretreatment of tissue sections with proteinase K and microwave irradiation, improved the detection of apoptotic cells.