Effects of endotoxin tolerance on Propionibacterium acnes-primed lipopolysaccharide hepatic injury

Prolonged hepatomegaly in mice that cannot inactivate bacterial endotoxin

Transient hepatomegaly often accompanies acute bacterial infections. Reversible, dose-dependent hepatomegaly also occurs when animals are given intravenous infusions of bacterial lipopolysaccharide (LPS). We found that recovery from LPS-induced hepatomegaly requires a host enzyme, acyloxyacyl hydrolase (AOAH), that inactivates LPS. When we challenged Aoah(-/-) mice with low doses of LPS or gram-negative bacteria, their livers remained enlarged (as much as 80% above normal) many weeks longer than did the livers of Aoah(+/+) animals. When compared with livers from LPS-primed Aoah(+/+) mice, LPS-primed Aoah(-/-) livers had (1) more numerous and larger Kupffer cells, (2) intrasinusoidal leukocyte aggregates and activated sinusoidal endothelial cells, and (3) sustained production of interleukin (IL)-10 and messenger RNAs (mRNAs) for tumor necrosis factor (TNF), IL-10, and IRAK-M. Depleting Kupffer cells decreased the liver enlargement by ≈40%, whereas depletion of neutrophils, dendritic cells, natural killer (NK) cells, NK-T cells, or B cells had no effect. Pretreatment with dexamethasone almost completely prevented prolonged hepatomegaly in Aoah(-/-) mice, whereas neutralizing TNF or interleukin-1β was only partially effective. In contrast, an antagonistic antibody to the IL-10 receptor increased LPS-induced hepatomegaly by as much as 50%.

CONCLUSION

our findings suggest that persistently active LPS induces Kupffer cells to elaborate mediators that promote the accumulation of leukocytes within enlarged sinusoids. Large increases in IL-10 and several other modulatory molecules are unable to prevent prolonged hepatomegaly in mice that cannot inactivate LPS. The striking findings in this mouse model should encourage studies to find out how AOAH contributes to human liver physiology and disease.

Lipopolysaccharide sensing an important factor in the innate immune response to Gram-negative bacterial infections: benefits and hazards of LPS hypersensitivity

In this review, we summarize our investigations concerning the differential importance of CD14 and LBP in toll-like receptor 4 (TLR4)/myeloid differentiation protein-2 (MD-2)-mediated signaling by smooth and rough-form lipopolysaccharide (LPS) chemotypes and include the results obtained in studies with murine and human TLR4-transgenic mice. Furthermore, we present more recent data on the mechanisms involved in the induction of LPS hypersensitivity by bacterial and viral infections and on the reactivity of the hypersensitive host to non-LPS microbial ligands and endogenous mediators. Finally, the effects of pre-existing hypersensitivity on the course and outcome of a super-infection with Salmonella typhimurium or Listeria monocytogenes are summarized.

Down-regulation of TGFbeta1 and leptin ameliorates thioacetamide-induced liver injury in lipopolysaccharide-primed rats

Pretreatment with a low dose of bacterial endotoxin (lipopolysaccharide, LPS) caused the reduction of cytochrome P450 (CYP) enzymes and inflammatory factors which are capable of protecting the liver from a lethal LPS challenge. However, the effects of LPS pretreatment on the expression of transforming growth factor beta1 (TGFbeta1) and leptin in thioacetamide (TAA)-induced liver fibrosis remain unknown. In this study, Sprague-Dawley rats were pretreated intraperitoneally with LPS (5 mg/kg body weight) for 24 h, and subsequently treated with TAA (200 mg/kg body weight/ 3 days) for 1 month to examine the effects of LPS on TAA-injured rats. LPS pretreatment was associated with lower granulation and lower (P < 0.05) GOT/GPT than in TAA-injured rats. The LPS-pretreated group had less collagen (Sirius red histochemical staining). Semiquantitative RT-PCR showed that the levels of collagen 3 and TGFbeta1 mRNAs were lower (P < 0.05) in the liver of LPS-pretreated rats than in TAA-injured rats. TGFbetaRI mRNA in the liver of LPS-pretreated rats exceeded (P < 0.05) that in TAA-injured rats. LPS pretreatment reduced the leptin content (Western blot) below that of TAA-injured rats. These results imply that LPS pretreatment (endotoxin tolerance) alleviates the TAA-induced liver fibrosis of rats by reducing TGFbeta1 and leptin content.

Pivotal advance: alpha-galactosylceramide induces protection against lipopolysaccharide-induced shock

alpha-galactosylceramide, a natural killer T cell ligand, and its synthetic homolog, KRN7000, consistently influence IFN-gamma and TNF-alpha release, both mediators of LPS-induced shock. To modify the course of endotoxin shock, we injected KRN7000 at different time points of experimental systemic Shwartzman reaction. Mice treated with KRN7000 survived when it was injected within 2 h before and after LPS challenge. Mice survival was associated with low levels of T helper 1 (Th1) cytokines, such as IFN-gamma and TNF-alpha. By contrast, protection from endotoxin shock was associated with an increase of T helper 2 (Th2) cytokines, like IL-4 and IL-10. A role of Th2 cytokines in counteracting LPS-induced shock was supported by experiments in which the protection against Shwartzman reaction by KRN7000 was abrogated by in vivo coadministration of anti-Th2 cytokines antibodies. In addition, cytofluorimetric analysis showed that surviving animals have higher percentages of NKT-IL-10-positive cells and lower percentages of NKT-IFN-gamma and macrophages/TNF-alpha-stained cells than nonprotected mice. Taken together, our data demonstrate that KRN7000 treatment given at times near LPS challenge is protective for endotoxin shock inhibiting IFN-gamma and TNF-alpha release. Moreover, KRN7000-mediated protection occurs through an increased production of IL-4 and IL-10, which are mainly secreted by NKT cells. Since IFN-gamma release by NKT requires a longer TCR stimulation than that required for Th2 cytokines production, we demonstrate that timing of KRN7000 in vivo exposure affect the pattern of cytokines expression protecting animals by endotoxin shock.

Requirement for TLR9 in the Immunomodulatory Activity ofPropionibacterium acnes

Propionibacterium acnes (formerly Corynebacterium parvum) is part of the human flora and, as such, is associated with several human pathologies. It possesses strong immunomodulatory activities, which makes this bacterium interesting for prophylactic and therapeutic vaccination. The bacterial component(s) and the host receptor(s) involved in the induction of these activities are poorly understood. We show in this study that TLR9 is crucial in generating the characteristic effects of killed P. acnes priming in the spleen, such as extramedullary hemopoiesis and organ enlargement, and granuloma formation in the liver. Furthermore, the ability to overproduce TNF-alpha and IFN-gamma in response to LPS, lipid A, synthetic lipopeptide Pam(3)CysK(4), or whole killed bacteria was present in P. acnes-primed wild-type, but not TLR9(-/-), mice. Finally, P. acnes priming failed to induce enhanced resistance to murine typhoid fever in TLR9(-/-) mice. Thus, TLR9 plays an essential role in the induction of immunomodulatory effects by P. acnes. Because IFN-gamma is a key mediator of these effects, and enhanced IFN-gamma mRNA expression was absent in spleen and liver of P. acnes-primed TLR9(-/-) mice, we conclude that TLR9 is required for the induction of IFN-gamma by P. acnes.