EBNA1-specific CD4⁺ T-cell responses among 40 healthy volunteers. (A) IFNγ secretion of PBMCs in response to all EBNA1 peptides (Master mix) and subpools I-V by ELISPOT assays after stimulation for 1 week with autologous dendritic cells pulsed with all EBNA1 peptides. Ten of 20 representative PBMC stimulations from leukocyte concentrates are shown. (B) Each data point represents the frequency of IFNγ-expressing CD4⁺ T cells from each volunteer to one of 3 stimuli. The stimuli are indicated along the x-axis: medium (no stimulus), CMV (HCMV-derived CD8⁺ T-cell epitopes; Table S1), and EBNA1 (the master mix of all 51 overlapping peptides of EBNA1; Table S1). The frequency of IFNγ-positive CD4⁺ T cells of each individual is indicated by a diamond. The average frequency of IFNγ-positive CD4⁺ T cells for each of the 3 stimuli is indicated by the black bars.