In several countries pertussis is re-emerging, despite a high vaccination coverage. It is suggested that antigenic divergence between Bordetella pertussis vaccine strains and circulating strains, in particular with respect to pertactin, has contributed to pertussis re-emergence. Polymorphism in pertactin is essentially limited to region 1, which is composed of repeats and is located adjacent to an Arg-Gly-Asp motif implicated in adherence. Evidence is provided for the immunological relevance of polymorphism in region 1. Region 1 was found to contain a B-cell epitope recognized in both humans and mice. Furthermore, variation in region 1 affected antibody binding and, in a mouse respiratory infection model, the efficacy of a whole-cell vaccine. Moreover, passive and active immunization indicated that region 1 confers protective immunity. An mAb directed against a linear conserved epitope conferred crossimmunity against isolates with distinct pertactin variants. The results indicate an important role of region 1 of pertactin in immunity.

In the absence of opsonizing antibodies, Bordetella pertussis, the causative agent of pertussis, readily binds to phagocytes via complement receptor 3 (CR3). After opsonization with antibodies, binding is mediated by IgG receptors (FcgammaR). The effect of targeting B. pertussis to either FcgammaR or CR3 was studied. The fate of unopsonized B. pertussis, IgG-opsonized B. pertussis, and B. pertussis opsonized with bispecific antibodies (BsAbs) directed to CR3 or FcgammaRII/-III was compared. IgG antibodies mediated binding and phagocytosis of B. pertussis via FcgammaR by polymorphonuclear leukocytes (PMNL) in vitro. Opsonization of B. pertussis with BsAbs directed against either CR3 or FcgammaRII/-III facilitated PMNL phagocytosis; however, in vivo studies with BsAb revealed that FcgammaR-mediated uptake facilitates B. pertussis clearance, in contrast to uptake via CR3. Targeting of B. pertussis to FcgammaRII/-III in mice deficient in FcgammaRII or FcgammaRIII indicated that the protective effect is attributable to FcgammaRIII. Competition between uptake via CR3 or FcgammaR may determine the outcome of natural infection.