IL-6, IFN-gamma and TNF-alpha production by liver-associated T cells and acute liver injury in rats administered concanavalin A

Lymphocyte-mediated liver injury in alcohol-related hepatitis

The pathogenesis of alcohol-related liver disease (ALD) remains inadequately explained. Increasing alcohol intake is associated with an increased risk of ALD, but many heavy drinkers develop no liver damage. An explanation for ALD susceptibility requires theories that extend beyond a biochemical understanding of alcohol metabolism. Several hepatic cell populations are involved in the pathogenesis of liver injury. The liver-associated lymphocyte (LAL) response to alcohol intake plus immune stimulation may determine susceptibility to liver damage. We have isolated rat LALs and demonstrated the following: (1) Liver-associated lymphocytes differ from the peripheral blood lymphocyte pool; the CD8:CD4 ratio is higher in the LAL population than in peripheral blood. (2) Tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 production by these cells is suppressed by regular alcohol intake. (3) Tumor necrosis factor-alpha and interleukin-6 production by LALs is increased after parenteral administration of concanavalin A (Con A) and by Con A in in vitro LAL cultures obtained from healthy (control) and ethanol-consuming rats. (4) In vivo stimuli that lead to increased cytokine production by LALs lead, within 12-24 h, to increased hepatocyte necrosis [elevated alanine aminotransferase (ALT) levels] and apoptosis. (5) Liver-associated lymphocytes isolated from ethanol-consuming rats, transferred to non-ethanol-consuming rats, confer on the latter animals an ethanol-consuming response to Con A. (6) Cytokine release by LALs is quantitatively as significant as that from Kupffer cells after exposure to lipopolysaccharide. (7) In co-culture studies inhibition of TNF-alpha activity reduces hepatocyte apoptosis induced in the presence of activated LALs. (8) Finally, nuclear factor-kappa B inhibition decreases production of nitric oxide and TNF-alpha, with an associated reduction in hepatocyte apoptosis. In summary, our study findings support the suggestion that a role for LALs exists in the pathogenesis of alcohol and Con A-mediated liver disease.

CD44-deficient mice exhibit enhanced hepatitis after concanavalin A injection: evidence for involvement of CD44 in activation-induced cell death

Administration of Con A induces severe injury to hepatocytes in mice and is considered to be a model for human hepatitis. In the current study, we investigated the role of CD44 in Con A-induced hepatitis. Intravenous administration of Con A (20 mg/kg) caused 100% mortality in C57BL/6 CD44-knockout (KO) mice, although it was not lethal in C57BL/6 CD44 wild-type (WT) mice. Administration of lower doses of Con A (12 mg/kg body weight) into CD44 WT mice induced hepatitis as evident from increased plasma aspartate aminotransferase levels accompanied by active infiltration of mononuclear cells and neutrophils, and significant induction of apoptosis in the liver. Interestingly, CD44 KO mice injected with similar doses of Con A exhibited more severe acute suppurative hepatitis. Transfer of spleen cells from Con A-injected CD44 KO mice into CD44 WT mice induced higher levels of hepatitis when compared with transfer of similar cells from CD44 WT mice into CD44 WT mice. The increased hepatitis seen in CD44 KO mice was accompanied by increased production of cytokines such as TNF-alpha, IL-2 and IFN-gamma, but not Fas or Fas ligand. The increased susceptibility of CD44 KO mice to hepatitis correlated with the observation that T cells from CD44 KO mice were more resistant to activation-induced cell death when compared with the CD44 WT mice. Together, these data demonstrate that activated T cells use CD44 to undergo apoptosis, and dysregulation in this pathway could lead to increased pathogenesis in a number of diseases, including hepatitis.

A broad-spectrum caspase inhibitor blocks concanavalin A-induced hepatitis in mice

Fulminant hepatic failure (FHF) is a clinical syndrome resulting from massive death of liver cells or sudden and severe impairment of liver function. The causes of FHF are diverse and the overall mortality is very high. Recently, it became clear that apoptosis of hepatocytes is the critical cause of acute hepatic failure in FHF. It is well known that a family of cysteine proteases called caspase is one of the key mediators of the apoptotic pathway. Thus, caspases are attractive potential targets for the treatment of disorders resulting from excessive apoptosis. In this report, we examined the activity of a new caspase inhibitor, Xyz 033 mp. This nonpeptide inhibitor showed broad-spectrum caspase-inhibiting activity and protected primary rat hepatocytes from apoptotic death. In a mouse model of FHF induced by concavalin A (Con A), Xyz 033 mp suppressed elevated AST and ALT and specifically reduced IL-1 beta concentration. Also, Xyz 033 mp rescued mice from lethal experimental hepatitis induced by Con A. In addition, histological examinations indicated that Xyz 033 mp protected hepatocytes from the fatal apoptogenic effect of Con A. These results suggest that Xyz 033 mp may be a candidate therapeutic agent for FHF caused by massive apoptotic death of hepatocytes.

Importance of Kupffer cells for T-cell-dependent liver injury in mice

T cells seem to be responsible for liver damage in any type of acute hepatitis. Nevertheless, the importance of Kupffer cells (KCs) for T-cell-dependent liver failure is unclear. Here we focus on the role of KCs and tumor necrosis factor (TNF) production after T cell stimulation in mice. T-cell- and TNF-dependent liver injury were induced either by Pseudomonas exotoxin A (PEA), by concanavalin A (Con A), or by the combination of subtoxic doses of PEA and the superantigen Staphylococcus enterotoxin B (SEB). KCs were depleted by clodronate liposomes. Although livers of PEA-treated mice contained foci of confluent necrosis and numerous apoptotic cells, hardly any apoptotic cells were observed in the livers of Con A-treated mice. Instead, large bridging necroses were visible. Elimination of KCs protected mice from PEA-, Con A-, or PEA/SEB-induced liver injury. In the absence of KCs, liver damage was restricted to a few small necrotic areas. KCs were the main source of TNF. Hepatic TNF mRNA and protein production were strongly attenuated because of KC-depletion whereas plasma TNF levels were unaltered. Our results suggest that KCs play an important role in T cell activation-induced liver injury by contributing TNF. Plasma TNF levels are poor diagnostic markers for the severity of TNF-dependent liver inflammation.

Exaggerated hepatic injury due to acetaminophen challenge in mice lacking C-C chemokine receptor 2

Monocyte chemoattractant protein-1 is one of the major C-C chemokines that has been implicated in liver injury. The C-C chemokine receptor, CCR2, has been identified as the primary receptor that mediates monocyte chemoattractant protein-1 (MCP-1) responses in the mouse. Accordingly, the present study addressed the role of CCR2 in mice acutely challenged with acetaminophen (APAP). Mice genetically deficient in CCR2 (CCR2(-/-)) and their wild-type counterparts (CCR2(+/+)) were fasted for 10 hours before receiving an intraperitoneal injection of APAP (300 mg/kg). Liver and serum samples were removed from both groups of mice before and at 24 and 48 hours post APAP. Significantly elevated levels of MCP-1 were detected in liver samples from CCR2(+/+) and CCR2(-/-) mice at 24 hours post-APAP. Although CCR2(+/+) mice exhibited no liver injury at any time after receiving APAP, CCR2(-/-) mice exhibited marked evidence of necrotic and TUNEL-positive cells in the liver, particularly at 24 hours post-APAP. Enzyme-linked immunosorbent assay analysis of liver homogenates from both groups of mice at the 24 hours time point revealed that liver tissue from CCR2(-/-) mice contained significantly greater amounts of immunoreactive IFN-gamma and TNF-alpha. The in vivo immunoneutralization of IFN-gamma or TNF-alpha significantly attenuated APAP-induced liver injury in CCR2(-/-) mice and increased hepatic IL-13 levels. Taken together, these findings demonstrate that CCR2 expression in the liver provides a hepatoprotective effect through its regulation of cytokine generation during APAP challenge.

Ethanol-altered liver-associated T cells mediate liver injury in rats administered Concanavalin A (Con A) or lipopolysaccharide (LPS)

BACKGROUND

Recent work from our laboratory implicates T cells in the pathogenesis of alcoholic liver disease. We have studied the role of liver-associated T cells in acute hepatitis produced in control rats administered Concanavalin A (Con A) after adoptive transfer of T cells from alcohol-consuming animals.

METHODS

Liver-associated T cells from ethanol-consuming rats were transferred via tail vein to nonethanol-consuming rats. They then received Con A (20 mg/kg body weight) intravenously. This produced a severe hepatitis. Serum was collected for the assay of alanine aminotransferase (ALT) and cytokines.

RESULTS

Hepatic necrosis was accompanied by an increase in plasma levels of ALT, interleukin-6, and tumor necrosis factor-alpha. These increases correlated with increased production of interleukin-6 and tumor necrosis factor-alpha in culture of liver-associated T cells stimulated or unstimulated with Con A. Immunohistology staining showed increased infiltration of inflammatory cells comprised of neutrophils and mononuclear cells, which included greater numbers of CD4+ T cells in the portal tract areas and around the central vein. Focal and lobular necrosis was seen with inflammatory cells in the necrotic area. Hepatocytes isolated from the liver showed increased apoptosis compared with rats that received liver-associated T cells from nonethanol-consuming rats. Injection of endotoxin LPS, in the same model, was associated with less hepatocyte injury indicating a distinct role for T cells as opposed to Kupffer cells in this model of liver disease.

CONCLUSIONS

Chronic ethanol consumption induces a lesion in a pool of liver-associated T cells which can mediate liver injury after polyclonal mitogen activation.

Lectin-induced nitric oxide production

Considering that nitric oxide (NO) may be involved in anti-tumoral and anti-parasite lectin effects, in this report we investigated whether lectin induces NO production. Lectins from Canavalia brasiliensis, Dioclea grandiflora, Pisum arvense (PAA), and concanavalin A induced murine peritoneal cells to produce NO in vitro. PAA induced similar levels to that obtained with lipopolysaccharide plus interferon-gamma. NO production by adherent cells was significantly lower than that of unfractionated cells, suggesting a combination of lectin stimuli directly on macrophages and via lymphocyte stimulation. Ex vivo experiments showed that cells stimulated in vivo could maintain NO production in vitro without further stimuli. NO synthesis blockage in vivo can significantly increase cell numbers in draining lymph nodes after lectin injection compared to unblocked controls, suggesting an in vivo association of lectin stimuli and NO production. Taken together these data show that lectins can induce NO production both in vitro and in vivo.