These proteins therefore represent potential vaccine targets. The increase in pertussis outbreaks and the many adaptations observed in B. pertussis populations, including the downregulation of Prn, indicates that more potent pertussis vaccines are warranted. Here, using an integrated ��omics�� approach, we identified OmpP, OmpA, SphB1, Vag8, and BP2497 as in vivo expressed vaccine candidates. Stand-alone immunization with the autotransporters SphB1 and Vag8 induced significant protection against lower respiratory tract infection, at a level which was only 10- and 3-fold lower compared to the reference 3component aP vaccine, respectively. Thus far, four B. pertussis autotransporters have shown to confer protection in the mouse model, Prn, TcfA, SphB1, and Vag8, suggesting that these proteins represent an attractive class of protective Curculigoside antigens. Since aluminum adjuvants typically induce a strong T helper type 2 response and high levels of antibodies, we primarily focused on the contribution of antibodies to protection. Although all five selected vaccine candidates induced significant levels of specific serum IgGs, only rSphB1 and rVag8 conferred significant protection. A potential explanation for this result may be that only antibodies to rSphB1 and rVag8 opsonized B. pertussis. The inability of antibodies specific for rOmpP, rOmpA, and rBP2497 to successfully opsonize bacteria may be due to incorrect folding of the recombinant proteins, which is essential to induce bactericidal antibodies particularly to integral outer membrane proteins like OmpP and OmpA. At present, the exact mechanisms of protection induced by SphB1 and Vag8 remain unknown. Antibodies to these proteins may facilitate phagocytosis and subsequent killing, or result in the deposition of complement factors on the bacterial surface. Alternatively, antibodies may Arbutin neutralize the biological activity of these antigens. For instance, antibodies against Vag8 may enhance the susceptibility of B. pertussis to complement-mediated killing. Interestingly, SphB1 induced similar protection levels compared as Vag8, despite much lower opsonization levels.