Detection of test cell chimerism using fluorescence cytometry. Venous peripheral blood cells were isolated from the tail veins of C57Bl/6 (CD45.2⁺) and B6.BoyJ (CD45.1⁺) mice. Defined mixtures of nucleated blood cells from each mouse were stained with antibodies to CD45.1 (), CD45.2 (▪), or a nonspecific isotype control (□) and analyzed using fluorescence cytometry. Each histogram represents the staining profile of a single cell mixture. The white peak is the isotype control. The gray and black peaks represent CD45.1 and CD45.2 positive cells, respectively. The numbers in the upper right corner of each histogram show the expected percentages of CD45.1/CD45.2 for each histogram. CD45.1 and CD45.2 chimerism measured using fluorescence cytometry were consistently within 3% of the predicted value over a wide range of cell mixtures.