Adenoviral infection decreases mortality from lipopolysaccharide-induced liver failure via induction of TNF-alpha tolerance

TNF Tolerance in Monocytes and Macrophages: Characteristics and Molecular Mechanisms

Tumor necrosis factor (TNF) tolerance in monocytes and macrophages means that preexposure to TNF reduces the sensitivity in these cells to a subsequent restimulation with this cytokine. Differential effects arise following preincubation with both low and high doses of TNF resulting in absolute as well as induction tolerance affecting specific immunologically relevant gene sets. In this review article, we summarize the relevance of TNF tolerance in vivo and the molecular mechanisms underlying these forms of tolerance including the role of transcription factors and signaling systems. In addition, the characteristics of cross-tolerance between TNF and lipopolysaccharide (LPS) as well as pathophysiological aspects of TNF tolerance are discussed. We conclude that TNF tolerance may represent a protective mechanism involved in the termination of inflammation and preventing excessive or prolonged inflammation. Otherwise, tolerance may also be a trigger of immune paralysis thus contributing to severe inflammatory diseases such as sepsis. An improved understanding of TNF tolerance will presumably facilitate the implementation of diagnostic or therapeutic approaches to more precisely assess and treat inflammation-related diseases.

Agonistic Antibody to TLR4/MD-2 Protects Mice from Acute Lethal Hepatitis Induced by TNF-α

LPS is recognized by a heterodimer consisting of TLR4 and its coreceptor MD-2. LPS signal causes excessive inflammation and tissue damage. In this study, we show that a mAb to TLR4/MD-2 protected mice from acute lethal hepatitis caused by LPS/d-galactosamine. The protective effect of the mAb was not due to inhibition of LPS response, because serum TNF-alpha, which was induced by LPS and caused lethal hepatitis, was 10 times up-regulated by the mAb pretreatment. Moreover, this mAb induced antiapoptotic genes in liver in a TLR4/MD-2-dependent manner. These results demonstrated that an agonistic mAb to TLR4/MD-2 protected mice from LPS/d-galactosamine-induced acute lethal hepatitis by delivering a protective signal activating NF-kappaB through TLR4/MD-2.

Adenovirus Infection Dramatically Augments Lipopolysaccharide-Induced TNF Production and Sensitizes to Lethal Shock

We observed a remarkable synergism of adenoviruses and LPS in triggering the production of TNF in intact animals. We found that in mice pre-exposed to adenoviruses, LPS injections generated extremely high levels of TNF with altered kinetics. The elevated TNF synthesis stemmed mostly from posttranscriptional up-regulation of TNF production, although transcription of the TNF gene was also induced. Adenoviruses and LPS exhibited a significant but less dramatic synergism in the induction of IL-6, IFN-gamma, and NO. Only marginal changes were detected in the synthesis of a panel of other cytokines. Different serotypes of the virus showed practically identical effects. As deletion mutants lacking indispensable viral genes or UV inactivated virions exhibited similar activities as the infectious, wild-type virus, it seems unlikely that the viral genome plays any significant role in the phenomenon. Published data indicate that other viruses also show some kind of synergism with LPS, although by different cellular mechanisms. T cells and their IFN-gamma production--crucial in the synergism of influenza viruses and LPS--were dispensable in our experiments. We suggest that the phenomenon is probably a general one: an overlap between different molecular mechanisms detecting bacterial and viral pathogens and inducing mediators of nonspecific cell-mediated host defense. The synergism of viruses and LPS (bacteria) could be a concern in medical practice as well as in gene therapy experiments with high doses of recombinant adenoviruses.

Increased sensitivity to staphylococcal enterotoxin B following adenoviral infection

Staphylococcal enterotoxin B induces toxic shock and is a major virulence factor of staphylococcal diseases. We examined the effects of systemic adenoviral infection on responses to staphylococcal enterotoxin B in a murine model. We found that adenoviral infection markedly increases the severity of liver injury following exposure to staphylococcal enterotoxin B without d-galactosamine sensitization. In adenovirus-infected mice, staphylococcal enterotoxin B triggered a more profound hypothermia and increased apoptosis in the liver. Consistent with these observations, we also found that adenoviral infection primed for an increased production of gamma interferon in vivo and in vitro following stimulation with staphylococcal enterotoxin B. Gamma-interferon-knockout mice did not show increased sensitivity to staphylococcal enterotoxin B following adenoviral infection. These data suggest that a preexisting viral infection primes mice for subsequent staphylococcal enterotoxin B exposure, possibly via a gamma-interferon-mediated mechanism.

Effects of SNMC on inhibiting hepatocyte apoptosis in mice with fulminant hepatic failure

AIM: To study the effects of SNBC on inhibiting hepatocyte apoptosis in mice with fulminant hepatic failure (FHF).

METHODS: Mice were given lipopolysaccharide (LPS, ip) and D-galactosamine (D-GalN, 1 000 mg/kg, ip) to establish FHF model. Hepatocyte apoptosis was observed by pathological section. After treated with SNMC, the level of serum TNFa were tested by radioimmunoassay. The expression of caspase-3 in liver tissue was determined by in situ hybridization.

RESULTS: The level of serum ALT and total bilirubin (TBiL) remarkably increased in FHF mice. Hepatocyte apoptosis was observed at 6 hours and the level of serum TNFa and caspase-3 expression increased significantly (3.750.50 vs 0.770.08, P<0.01; 3 vs 0, P<0.01) in comparison with those in normal mice. Hepatocyte apoptosis were inhibited and hepatocyte necrosis decreased significantly after SNBC administration. And serum TNFa level and caspase-3 expression was significantly decreased as compared with those in mice of model group (P<0.01). Hepatocyte apoptosis was gradually decreased with the action time of SNMC in mice. However, there was no significant difference between groups with different action time and doses of SNMC (P>0.05).

CONCLUSION: SNMC can protected hepatocytes from apoptosis in mice with FHF and the mechanism was associated with its inhibitory effect on the pathway of hepatocyte apoptosis.

Adenovirus vectors activate survival pathways in lung epithelial cells

Airway epithelial cells are often the sites of targeted adenovirus vector delivery. Activation of the host inflammatory response and modulation of signal transduction pathways by adenovirus vectors have been previously documented, including activation of MAP kinases and phosphatidylinositol 3-kinase (PI3-kinase). The effect of activation of these pathways by adenovirus vectors on cell survival has not been examined. Both the PI3-kinase/Akt and ERK/MAP kinase signaling pathways have been linked to cell survival. Akt has been found to play a role in cell survival and apoptosis through its downstream effects on apoptosis-related proteins. Constitutive activation of either PI3-kinase or Akt blocks apoptosis induced by c-Myc, UV radiation, transforming growth factor-β, Fas, and respiratory syncytial virus infection. We examined the effect of adenovirus vector infection on activation of these prosurvival pathways and its downstream consequences. Airway epithelial cells were transduced with replication-deficient adenoviral vectors containing a nonspecific transgene, green fluorescent protein driven by the cytomegalovirus promoter, or an empty vector with no transgene. They were then exposed to the proapoptotic stimulus actinomycin D plus TNF-α, and evidence of apoptosis was evaluated. Compared with the cells treated with actinomycin/TNF alone, the adenovirus vector-infected cells had a 50% reduction in apoptosis. When we examined induction of the prosurvival pathways, ERK and AKT, in the viral vector-infected cells, we found that there was significant activation of both Akt and ERK.

Blood brain barrier permeability in acute liver necrosis of mice

AIM: To study the permeability of the blood brain barrier (BBB) in a mouse model of acute liver necrosis.

METHODS: Male Balb/c mice were divided into 4 groups. In one group, mice were intraperitoneal of lipopolysaccharide (LPS, 10mg/kg) with D-galactosamine (GalN, 800 mg/kg) to induce acute liver necrosis. Other groups were controls. Serum levels of alanine transaminase (ALT) were determined and the liver tissues were fixed for histopathological analysis. The permeability of BBB in mice was investigated with Evans blue (EB).

RESULTS: The serum levels of ALT were increased mildly in mice, which were administration of LPS or GalN alone. And no animals died. But the levels of ALT began to increase at 6 hours (41.89±14.57 mat/L), and reached a maximal level at 12 hours (170.30±16.13 mat/L) after injection with both LPS and GalN. Mice began to die at 6 hours, and at 9 hours after injection, the rate of lethality reached an extremely high level of 66.6%. The liver became massive or submassive necrosis. The concentration of EB in brain was significantly increased in ALF models compared with other groups.

CONCLUSION: The permeability of BBB is increased in acute liver necrosis model. It may be the mechanism of the brain edema.