Vaccinia-specific CD4 and CD8 amplification leads to an increase in the frequency of effector–memory cells. (a) Percentage of BrdU+ cells in CD8 and CD4 T cells of five vaccinated individuals and two unvaccinated individuals after fresh PBMCs infected with either 1 pfu/cell vaccinia strain or medium alone were cultured for 3 d in the presence of BrdU (background subtracted). The number of IL-2–producing cells in the CD4 population was estimated by flow cytometric analysis at 48 h after antigenic stimulation (0–80 IL-2–producing cells/million CD4+ cells). (b) Representative flow cytometric analyses show IFN-γ production in vaccinia-specific T cells expanded for 7 d and restimulated on day 7 by monocytes infected with vaccinia for an additional 18 h at 1 pfu/cell (unvaccinated and long-term vaccinated individuals).
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