In our ongoing efforts to develop a
vaccine against Streptococcus suis
infection, we tested the potential of S. suis
enolase (SsEno), a recently described S. suis adhesin with
fibronectin-binding activity, as a
vaccine candidate in a mouse model of S. suis-induced
septicemia and
meningitis. Here, we show that SsEno is highly recognized by sera from convalescent pigs and is highly immunogenic in mice. Subcutaneous immunization of mice with SsEno elicited strong
immunoglobulin G (
IgG) antibody responses. All four
IgG subclasses were induced, with
IgG1,
IgG2a and
IgG2b representing the highest titers followed by
IgG3. However, SsEno-vaccinated and nonvaccinated control groups showed similar mortality rates after challenge
infection with the highly virulent S. suis strain 166'. Similar results were obtained upon passive immunization of mice with hyperimmunized rabbit
IgG anti-SsEno. We also showed that anti-SsEno
antibodies did not increase the ability of mouse phagocytes to kill S. suis in vitro. In conclusion, these data demonstrate that although recombinant SsEno formulated with
Quil A triggers a strong antibody response, it does not confer effective protection against
infection with S. suis serotype 2 in mice.