Induction of BLP tolerance protects TLR4 deficient mice against gram negative sepsis via enhanced bacterial clearance, in a process independent of the neutrophil.

摘要

INTRODUCTION: Toll like receptors (TLR's) are highly conserved pathogen pattern recognition receptors. As a result, TLR4 deficient mice are highly susceptible to Gram Negative (G-ve) sepsis. We assessed whether pretreatment of TLR4 deficient mice with BLP, a TLR2 ligand, could induce tolerance to a subsequent G-ve Salmonella Typhimurium (S.Typhi) challenge. METHODS: In three separate experiments C3H/HeN, C3H/HeJ and BLP pre-treated C3H/HeJ mice (each n = 10) were exposed to 0.25 x 10(6) CFU S.Typhi. Firstly, mortality was observed. Secondly, animals were divided and harvested at 24 and 48 hours. Blood, lungs, liver and spleen were harvested and homogenized in 2mls sterile PBS. Following serial dilution, samples were incubated on trypticase soy agar for 24 hrs at 37 degrees C for determination of bacterial CFU. Thirdly, all animals were depleted of neutrophils by pretreatment with cyclophosphamide (250mg/kg I.P.) and bacterial CFU were determined in a similar manner. RESULTS: Pre-treatment with BLP results in a significant survival benefit in C3H/HeJ mice (p < 0.0001) following challenge with 0.25 x 10(6) CFU S.Typhi. This phenomenon is partially explained by the differences seen with bacterial clearance rates. BLP pre-treatment results in significantly increased rates of bacterial clearance from the bloodstream and significant attenuation of bacterial colonization of the lung, liver and spleen. Neutrophil depletion did not reduce the beneficial differences observed in bacterial clearance rates. CONCLUSION: BLP, a ligand for TLR2, induces tolerance in C3H/HeJ mice to a G-ve S.Typhi challenge. This phenomenon appears to be mediated by greatly enhanced bacterial clearance from both the bloodstream and the solid organs in a process independent of the neutrophil.