Protective efficacy of recombinant Yersinia outer proteins against bubonicplague caused by encapsulated and nonencapsulated Yersinia pestis

To evaluate the role of Yersinia outer proteins (Yops) in conferring protec tive immunity against plague, six yap loci from Yersinia pestis were indivi dually amplified by PCR, cloned, and expressed in Escherichia coli. The rec ombinant proteins were purified and injected into mice. Most Yop-vaccinated animals succumbed to infection with either wild-type encapsulated Y. pesti s or a virulent, nonencapsulated isogenic variant. Vaccination with YpkA si gnificantly prolonged mean survival time but did not increase overall survi val of mice infected with the nonencapsulated strain. The only significant protection against death was observed in YopD-vaccinated mice challenged wi th the nonencapsulated strain.