Proliferation, apoptosis and p53 protein expression in adult T-cell leukemia (ATL) cells were investigated. Twenty peripheral blood tissue specimens (PBTS) comprising 7 cases of acute type ATL, 7 cases of chronic type ATL and 6 other leukemias were examined by means of antigen retrieval and the polymer method employing anti-Ki67 antigen (MIB-1), anti-cleaved caspase-3, anti-single stranded DNA and three kinds of anti-p53 protein antibodies including DO7. Most acute and chronic cases of ATL

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... ded more than 10% MIB-1-positive proliferating leukemia cells and more than 1% cleaved caspase-3positive apoptotic cells. Some cells which were positive for both MIB-1 and anti-cleaved caspase-3 antibody were observed in acute type ATL. Nuclear deposition of p53 protein labeled by DO7 was often found in acute type (p < 0.05). Within the medium-sized population of ATL cell nuclei, DO7-positive ATL cells had a smaller nuclear area factor (long axis x short axis) than DO7-negative ATL cells. A few proliferating ATL cells entered apoptosis, and the appearance of a subclone of ATL cells with nuclear deposition of p53 protein labeled by DO7 characterized acute type. 〔J Clin Exp Hematopathol 48(1) : 1-10, 2008〕 Keywords: adult T-cell leukemia (ATL), peripheral blood tissue specimen (PBTS), proliferation, apoptosis, double immunostaining MATERIALS AND METHODS Twenty specimens were examined in this study. Specimens were formalin-fixed and paraffin-embedded PBTS from patients with ATL acute type (n = 7), ATL chronic type 1