Expression and Immunogenicity of Hemagglutinin A from Porphyromonas gingivalis in an Avirulent Salmonella enterica Serovar Typhimurium Vaccine Strain

Porphyromonas gingivalis is a major etiologic agent of periodontitis, a chronic inflammatory disease that ultimately results in the loss of the supporting tissues of the teeth. Previous work has demonstrated the usefulness of avirulentSalmonella enterica serovar Typhimurium strains as antigen delivery systems for protective antigens of pathogens that colonize or cross mucosal surfaces. In this study, we constructed and characterized a recombinantS. enterica serovar Typhimurium avirulent vaccine strain which expresses hemagglutinin A and carries no antibiotic resistance markers. HagA, a major virulence-associated surface protein, is a potentially useful immunogen that contains an antigenic epitope which, in humans, elicits an immune response that is protective against subsequent colonization byP. gingivalis . ThehagA gene, including its promoter, was cloned into a balanced-lethalSalmonella vector and transferred to the vaccine strain. Heterologous expression of HagA was demonstrated in bothEscherichia coli JM109 andS. enterica serovar Typhimurium vaccine strain χ4072. The HagA epitope was present in its native configuration as determined by immunochemistry and immunoelectron microscopy. Purified recombinant HagA was recognized by sera from mice immunized with theS. enterica serovar Typhimurium vaccine strain. The HagA-specific antigen of the vaccine was also found to be recognized by serum from a periodontal patient. This vaccine strain, which expresses the functional hemagglutinin protein, induces a humoral immune response against HagA and may be useful for developing a protective vaccine against periodontal diseases associated withP. gingivalis .