Two-color flow cytometric analysis of intracellular IFNγ and IL-4 expression by EBV-specific CD8⁺ T cells. T cells were unstimulated (A, C, and E) or stimulated for 6 hours with PMA and ionomycin (B, D, and F), as described in Materials and Methods. T-cell lines from three healthy adult donors were tested: JTC (A and B), KR (C and D), and MJC (E and F).