Mice intradermally-inoculated with the intact lipopolysaccharide, but not the lipid A or O-chain, from Francisella tularensis LVS rapidly acquire varying degrees of enhanced resistance against systemic or aerogenic challenge with virulent strains of the pathogen.

The present study examines the relationship between the structure and important biological effects of the lipopolysaccharide (LPS) of the intracellular bacterial pathogen, Francisella tularensis LVS. It shows that treating mice with sub-immunogenic amounts of intact F. tularensis LPS rapidly induces an enhanced resistance to intradermal or aerogenic challenge with strains of the pathogen of varying virulence. However, neither the free Lipid A nor core-O-chain produced by mild acid hydrolysis of LPS appeared able to elicit this host defense mechanism.