Kinetics of vaccine-specific and bystander cytokine production by Th_mem cells following booster vaccination (week 0) with TT. Two representative examples are shown. Characteristic Th1 (IFNγ and IL-2) and Th2 (IL-13) cytokines are produced following in vitro restimulation with TT and detected by ELISPOT assay. Parallel changes in the number of cytokine-producing cells are seen against PPD and (to a lesser extent) against C albicans but not against Ctrl1 or Ctrl2. Data for each time point represent the mean number of spots ± SD of triplicate wells of antigen-stimulated cultures after subtracting the mean number of spots in the corresponding negative control. The mean number of spots in the controls was always less than 5 spots per 2 × 10⁵ PBMNCs.