Fig. 1. Flow cytometric analysis illustrating DNA and protein content at indicated time points in primary human T lymphocytes from a representative experiment. Top, cell cycle distributions of quiescent (Day 0 Untreated) and PHA-treated (Day 3 PHA), IL-2-treated (Day 6 IL-2), and IL-2-/IFN--treated (Day 6 IL-2+IFN-) cells, determined by plotting the intensity of 4',6-diamidino-2-phenylindole propidium iodide fluorescence as a function of the cell number. Bottom, DNA and protein content in quiescent and PHA-, IL-2-, and IL-2-/IFN--treated cells, determined by plotting the intensity of 4',6-diamidino-2-phenylindole and SR101 fluorescence, respectively. Cells appearing in G2 in the quiescent (Day 0 Untreated), PHA-treated (Day 3 PHA), and IL-2-/IFN--treated (Day 6 IL-2+IFN-) groups probably represent aggregated cells from G1 because no G2 cells were detected at these time points (top).