Whether the parameters we evaluated are the only ones that differ after administration of the two vaccine types, we do not know. Other parameters within the T cell compartment could be involved, GDC0199 like TH17 cells. Their role in protection was suggested from murine studies, in which aP vaccination induces TH2 and TH17 responses, but only the latter seem necessary for protection . However, the situation in humans is quite
different, as after aP vaccination a mixed TH1–TH2 phenotype is observed, therefore not excluding a role for TH1 in protection . Moreover, B cell memory might also be influenced by vaccine type. Dutch studies show that wP vaccinated children have detectable B cell memory responses up to 5 years after MEK inhibitor drugs the last booster dose  and . However, up to 2 years after a booster vaccine, children who received aP vaccines at infancy induced better B cell memory responses compared to those primed with a wP vaccine  and . As protection appears to be better for wP vaccinated children , ,  and , this supports the hypothesis
that B cell memory is not the limiting factor for protection for the currently used vaccines. Even though the cohorts included here are relatively small, an important strength of this study was that we obtained the precise records of all the vaccine data for all the children. However, we cannot rule out that some of the children may have boosted their immune responses by natural exposure to Bp, even if none of the children declared having suffered from whooping cough or having been in contact with a whooping cough patient. Serum levels of Bp-specific antibodies that were measured as part of a study on memory B cell responses and will be published separately, indicated that out of the 23 children in
this study, only one had an elevated anti-PT Metalloexopeptidase IgG serum level, a marker for recent infection (>125 IU/mL, data not shown)  and . This subject belonged to the group of wP-vaccinated children, but sensitivity analysis revealed that this did not impact the described differences between wP- and aP-vaccinated children. It is therefore unlikely that the results in this study have been confounded by natural boosting of pertussis-specific immune responses. We also found antigen-dependent differences in the memory immune responses. More children responded by proliferation or cytokine production to stimulation with FHA compared to PT. It should be noted that only PT is specific for Bp, while responses to FHA might also be the result of exposure to other Bordetella species or cross-reactivity with other bacteria, including Haemophilus influenza . The observed difference may thus potentially be due to non-specific boosting.