However, persistence of detectable antibody levels is relatively short, and can therefore not explain long-term protection. More recently it was shown that vaccination induces antigen-specific memory B cells, still detectable several years after vaccination despite waning antibody levels [35] and [36]. Moreover, the induction upon infection or vaccination of distinct T cell populations, TH1, TH17, TH2 and regulatory T cells, has been established in animal models, as well as their role in protection [15], [16], [17], [18], [19], [20] and [21]. We have previously shown this website that in humans, distinct T cell subsets are induced shortly after vaccination

or infection [22], [23], [24] and [25], and

here we show that several years after vaccination, memory T cells with mainly an effector memory phenotype (CD45RA−CCR7−) are detected in a high percentage of 9- to 12-years old children. Upon in vitro stimulation, these cells proliferate (79% of the children) and produce cytokines (65%) in response to at least one of the antigens PT or FHA. In 60% of the children, we could also detect proliferation of CD8+ T cells in response to PT and/or FHA stimulation, supporting a role of CD8+ T cells in Bp-specific immunity, in line with our previous finding that FHA-specific CD8+ T cells contribute to IFN-γ production [37]. Recent epidemiological studies in several countries with high vaccination coverage have indicated that teenagers who received an aP vaccine as an infant were Luminespib chemical structure more at risk to develop pertussis than wP primed children [2], [9], [38] and [39]. Other studies suggest that this is due to a more rapid waning of aP compared to wP vaccine-induced immunity and have shown that the rate of vaccine

failure gradually increases as the interval from the last aP vaccine dose increases [10] and [11]. In our study, we demonstrated that the vaccine type used for primary vaccination influences the immune response detected in 9- to 12-year old children. Cytokine response were broader after wP vaccination, with 88% of wP-vaccinated children being positive for PT- or FHA-induced cytokine below responses, while this was the case only for 50% of the aP-vaccinated children. Also, the PBMC from wP-primed children proliferated equally well in response to Bp antigens compared to aP-primed children, although the time since the last booster was longer in the former group. The frequency of children responding with both proliferation and cytokine production is twice as high for wP-compared to aP-vaccinated children. Thus, for the first time, we provide evidence that recently revealed differences in protection may be traced back to differences at the immunological level, both showing that wP-vaccines compare favorably to aP-vaccines.