Intracellular expression of green fluorescent protein (ZsGreen) fused with TNF-α in HEK293A cells determined by flow cytometry. ZsGreen fused with common (a) and Arg8His (b) TNF-α is visualized using histogram plots, representing two of 36 samples analyzed 72 h post-transfection. The M marker indicates the region for positive cells, determined separately in each flow cytometry experiment, in relation to the fluorescence signal from negative controls. Signals from cells regarded as negative, that is, transfected with a nonfluorescence vector, are due to autofluorescence, which increased with the lipofectamine treatment. Histogram statistics: A/Sn: 2497 mean fluorescence units within M, 39% positive cells of a total of 12 260 cells; I/St: 2342 mean fluorescence units within M, 31% positive cells of a total of 11 861 cells.