To the ongoing discussion on the presence of "false positive" apoptotic cells in peripheral blood detected by the DNA strand break assays let me add our recent observation. Specifically, we have found that eosinophils' granules nonspecifically bind directly fluorochrome-conjugated triphosphonucleotides in the absence of TdT. The reaction occurs even at 0 degrees centigrade. These cells, thus, without an adequate control, may be erronously classified as apoptotic cells. I am disclosing this information prior to publication (manuscript in preparation) to alert those who may have encountered this problem to prevent mis-interpretation of their data. Interestingly, the two step TdT reactions, utilizing digoxygenin or biotin labels, do not show this reaction. Zbigniew Darzynkiewicz
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