Download Pertussis is a highly contagious infectious disease of the respiratory

English summary
Pertussis is a highly contagious infectious disease of the respiratory tract which is caused by
Bordetella pertussis. Before widespread introduction of vaccination against pertussis, almost
every child contracted pertussis. The disease is most severe in neonates and children under the
age of 1. Introduction of mass vaccination reduced the number of pertussis cases significantly
and resulted in a 10-fold decrease in pertussis mortality in the Netherlands in the late 1950s.
Despite vaccination, pertussis remained endemic. A major epidemic occurred in the
Netherlands in 1996. Since the 1996 outbreak, the Netherlands now has an epidemic pertussis
cycle with peaks every 2 to 3 years during the last decade. Also in several other European
countries, as well as Canada, The United States and Australia, a re-emergence of pertussis
was observed. Several explanations were proposed for the sudden increase of pertussis in the
Netherlands including waning immunity in adolescents and adults, increased reporting,
improved diagnosis of the disease and the adaptation of the B. pertussis population. In the
Netherlands, pathogen adaptation has probably played an important role in the resurgence of
pertussis. Vaccine adapted strains showed polymorphisms in two proteins implicated in
protective immunity: P.69 Prn and Ptx. The role of P.69 Prn in protective immunity has been
well documented in both humans and in animal models. Furthermore, P.69 Prn is present in
several of the currently most used ACVs.
Until recently, relatively little was known about the antibody response to P.69 Prn, the
location of epitopes on P.69 Prn and the role of variation in Prn on immune evasion. Variation
in the variable region1 was described to affect the Ab response to this region, but no direct
evidence or a feasible mechanism for immune evasion was described. The goal of this thesis
was to identify the location of (protective) epitopes to which human Abs are directed, and to
investigate the role of variation in P.69 Prn and the implications for the anti-P.69 Prn Ab
response.
Our results clearly indicate that Prn has evolved several ways to escape antibody and possibly
phage binding. We showed that the N-terminus of P.69 Prn harbors important epitopes.
Furthermore, our data suggests that the variable region1 has evolved to hide those important
epitopes from immune recognition and possibly phage binding. In addition, Prn has several
other flexible (and variable) loops that are employed to hide adjacent epitopes from the
immune system (epitope masking). The N- and C-termini of P.69 Prn interact physically,
which results in the masking of a part of Prn. Since the C-terminus has a linear structure that
folds towards the N-terminus, it is likely that the Ab response to this region is less efficient
then an Ab response directed to the conformational epitopes located in parts of the molecule
that are covered by the C-terminus (conformational masking). The loops that are exposed, e.g.
region1, region2, and several other loops, were shown to be highly variable (antigenic
variation). We showed that deletion of the variable regions does not improve protection
against infection. Apparently deletion of the decoy regions does not automatically skew the
Ab response towards the conserved protective epitopes. However, we have shown that it is
possible to employ synthetic peptides to induce a protective response towards conserved and
protective epitopes.
The results presented in this thesis have shed new light on the mechanisms employed by
bacteria, and B. pertussis in particular, to evade immune recognition. These results will
facilitate the development of new, possibly synthetic, but mainly more effective vaccines.
English keywords
Bordetella pertussis
P.69 Pertactin
Immune evasion
Epitope mapping
Conformational epitopes
Peptide loops
Synthetic peptide vaccines
Protein expression
Epitope polymorphism
Antibody responses