NK cell proliferation in response to HCMV-infected fibroblasts. (A) CFSE-labeled PBLs from an HCMV⁺ donor were cocultured with mock- and Towne-infected (MOI = 1) MRC-5 cells as described in “Materials and methods.” Flow cytometry analysis was carried out at day 7, after staining cells with anti-NKG2C or -NKG2A mAbs; numbers correspond to the proportions of dividing and nondividing cells in NKG2C⁺ and NKG2A⁺ populations, calculated as described in “Materials and methods.” The experiment is representative of 6 performed. (B) PBLs were stimulated with Towne-infected fibroblasts as described in panel A, and flow cytometry analysis was carried out at different time points with anti-CD3-PerCP and anti-CD56-PE, counting the numbers of recovered cells. The percentages and the calculated numbers of NK- and T-cell populations are represented.