Antigenic variants in Bordetella pertussis strains isolated from vaccinated and unvaccinated children

Bordetella pertussis shows polymorphism in two proteins, pertactin (Prn) an d 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 b y vaccination. The recent Italian clinical trial provided the opportunity t o compare the frequencies of Prn and PT S1 subunit variants in strains isol ated from unvaccinated children, and from children vaccinated with two acel lular 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 strain s. The B. pertussis strains used to produce the vaccines administered in th e 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 l owest in the strains isolated from vaccinated groups, suggesting that Prn1 strains are more affected by vaccine-induced immunity than Prn2 and Prn3 st rains. Only one PT 51 type (S1A) was observed in the examined strains, whic h 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 DN A fingerprinting revealed that three fingerprint types predominate, represe nting more than 70% of the strains. Prn2 strains showed a greater variety o f fingerprint types compared to Prn3, suggesting that Prn3 has emerged more recently. The results are discussed in the light of vaccine-driven evoluti on.