The live vaccine strain of Francisella tularensis replicates in human and murine macrophages but induces only the human cells to secrete proinflammatory cytokines.

Francisella tularensis is the highly infectious agent of tularemia, a disease that can prove fatal in humans. An attenuated live vaccine strain (LVS) of this bacterium is avirulent in man but produces lethal illness in mice. As a step toward understanding the species specificity of the LVS, we compared its interactions with murine and human leukocytes.