Beneficial or Deleterious Effects of a Preexisting Hypersensitivity to Bacterial Components on the Course and Outcome of Infection

ABSTRACTPriming with heat-killed Propionibacterium acnesenhances the sensitivity of mice to lipopolysaccharide (LPS) and other biologically active bacterial components. We show that P. acnespriming has protective and deleterious effects on a subsequent serovar Typhimurium infection. It may result in a complete protection or prolonged survival, or it may accelerate mortality of the infected mice, depending on the number of serovar Typhimurium bacteria administered and on the degree of LPS hypersensitivity at the time of infection. Both effects of P. acnes-induced hypersensitivity are mediated by gamma interferon (IFN-γ) and are based on a differential activation of the innate immune mechanisms which recognize and react against the LPS present in infecting bacteria. In P. acnes-primed mice null for LPS-binding protein (LBP−/−mice), the impaired LPS recognition, due to the absence of LBP, resulted in a higher resistance to serovar Typhimurium infection. A similar P. acnespriming of mice had a protective, but no deleterious effect on a subsequent L. monocytogenesinfection. This effect was IFN-γ dependent but independent of LBP.