Cytometry. Part A : the journal of the International Society for Analytical Cytology
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Stat5(1) (Signal Transducer and Activator of Transcription 5) is normally phosphorylated and activated by Janus kinases. In cells transformed with BCR/ABL, Stat5 is constitutively activated by promiscuous phosphorylation. Cytometry of intracellular antigens can be used to evaluate cell treatments affecting gene expression, because it precisely provides the fraction of affected cells and the quantitative change in expression. Here, we asked whether we could measure a phosphorylated epitope on Stat5 by cytometry, and whether that measurement would respond to Bcr/Abl inhibition. ⋯ We have developed a sensitive cytometric assay for Bcr/Abl kinase activity in human hematopoietic cell lines.