Antigenic variants in Bordetella pertussis strains isolated from
vaccinated and unvaccinated children.
Mastrantonio P, Spigaglia P, van Oirschot H, van der Heide HG, Heuvelman K,
Stefanelli P, Mooi FR.
Department of Bacteriology and Medical Mycology, Istituto Superiore di Sanita,
Rome, Italy. pmastran@iss.it
Bordetella pertussis shows polymorphism in two proteins, pertactin (Prn) and the
pertussis toxin (PT) S1 subunit, which are important for immunity. A previous
study has shown antigenic shifts in these proteins in the Dutch B. pertussis
population, and it was suggested that these shifts were driven by vaccination.
The recent Italian clinical trial provided the opportunity to compare the
frequencies of Prn and PT S1 subunit variants in strains isolated from
unvaccinated children, and from children vaccinated with two acellular and one
whole-cell pertussis vaccine. Four Prn variants (Prn1, Prn2, Prn3 and Prn5) were
found in the 129 strains analysed. Prn1, Prn2 and Prn3 have been described
previously, whereas Prn5 is a novel variant. Prn1, Prn2, Prn3 and Prn5 were
found in, respectively, 6, 41, 51 and 2% of the strains. The B. pertussis
strains used to produce the vaccines administered in the clinical trial were
found to produce Prn1, or a type which differed from Prn1 in one amino acid. The
frequency of the Prn1 variant was found to be lowest in the strains isolated
from vaccinated groups, suggesting that Prn1 strains are more affected by
vaccine-induced immunity than Prn2 and Prn3 strains. Only one PT S1 type (S1A)
was observed in the examined strains, which was distinct from the types produced
by the vaccine strains (S1B and S1D). The S1A type also predominates in the
Dutch B. pertussis population. The genetic relationship among B. pertussis
strains analysed by IS1002-based DNA fingerprinting revealed that three
fingerprint types predominate, representing more than 70% of the strains. Prn2
strains showed a greater variety of fingerprint types compared to Prn3,
suggesting that Prn3 has emerged more recently. The results are discussed in the
light of vaccine-driven evolution.
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