Histologic sectioning produces TUNEL reactivity - A potential cause of false-positive staining

Objective.-To determine if the DNA strand breaks caused by tissue sectionin g result in terminal deoxynucleotidyl transferase-mediated deoxyuridine tri phosphate nick end-labeling (TUNEL) reactivity. Methods.-The incidence and location of TUNEL-positive nuclei were determine d in 5- and 15-mu m sections of human stomach. Five- and 15-mu m sections o f tonsil were stained as a positive control. Results.-In 5-mu m gastric sections, 69% of nuclei were labeled; in 15-mu m sections, only 30% were labeled. In the latter sections, almost all labele d nuclei were located at the cut surface of sections. Labeled nuclei did no t have apoptotic morphology. Apototic bodies and tingible body macrophages were labeled throughout 15-mu m sections of tonsil. Conclusions.-Tissue sectioning creates TUNEL reactivity. The morphologic fi ndings on routine stains should be considered the gold standard for the det ection of apoptosis on tissue sections.