Specificity of TUNEL method depends on duration of fixation

Recent evidence has suggested that apoptosis plays an important role in var ious diseases, but concerns about the specificity of the TUNEL method for d etecting apoptosis have been raised, The purpose of the present study was t o investigate the specificity of the TUNEL method by using immersion and pe rfusion fixed tissues from both normal rats and rats with heart failure. Al though a few positive cells were observed in perfusion fixed tissues, a sig nificant number of positive cells were observed in immersion fixed tissues, especially when fixed tissues were kept for an extended time before the TU NEL assay was applied. The results of TUNEL staining should be interpreted with caution. When immersion fixation is used, fixed tissues should be assa yed by the TUNEL method before the DNA degenerates.