Abstract
Francisella tularensis can cause fatal respiratory tularemia in humans and animals and is increasingly being isolated in the United States and several European countries. The correlates of protective immunity against this intracellular bacterium are not known, and currently there are no licensed vaccines available for human use. Cell-mediated immunity has long been believed to be critical for protection, and the importance of humoral immunity is also now recognized. Furthermore, synergy between antibodies, T cell-derived cytokines, and phagocytes appears to be critical to achieve sterilizing immunity against F. tularensis. Thus, novel vaccine approaches should be designed to induce robust antibody and cell-mediated immune responses to this pathogen.