Vaccine-specific and bystander cytokine production in 12 individuals following booster vaccination with TT. Responses are shown at the week of maximal TT (Wk Max TT) response and are compared with the prevaccine (Wk 0) response. Cytokine responses were measured by ELISPOT assay after 40 hours of in vitro culture and are reported as the mean number of spots ± SD of triplicate wells of antigen-stimulated cultures after subtracting the corresponding negative control. The mean numbers of spots in the controls were always less than 5 spots per 2 × 10⁵ PBMNCs.