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Background & Aims Complement is involved in the development of alcoholic liver disease in mice; however, the mechanisms for complement activation during ethanol exposure have not been identified. C1q, the recognition subunit of the first complement component, binds to apoptotic cells, thereby activating the classical complement pathway. Since ethanol exposure increases hepatocellular apoptosis, we hypothesized that ethanol-induced apoptosis would lead to activation of complement via the classical pathway. Methods Wild-type and C1qa-/- mice were allowed free access to ethanol containing diets or pair-fed control diets for 4 or 25 days. Results Ethanol feeding for 4d increased apoptosis of Kupffer cells in both wild-type and C1qa-/- mice. Ethanol-induced deposition of C1q and C3b/iC3b/C3c was co-localized with apoptotic Kupffer cells in wild-type, but not C1qa-/-, mice. Furthermore, ethanol-induced increases in TNFα and IL-6 expression at this early time point were suppressed in C1q-deficient mice. Chronic ethanol feeding (25d) increased steatosis, hepatocyte apoptosis, and activity of serum alanine and aspartate aminotransferases in wild-type mice. These markers of hepatocyte injury were attenuated in C1qa-/- mice. In contrast, chronic ethanol (25d)-induced increases in CYP2E1 expression and oxidative stress did not differ between wild-type and C1qa-/- mice. Conclusions For the first time, these data indicate that ethanol activates the classical complement pathway via C1q binding to apoptotic cells in the liver and that C1q contributes to the pathogenesis of ethanol-induced liver injury.

The innate immune system has been implicated in the pathogenesis of alcoholic liver disease. Although innate immunity is usually considered an early response to injury, previous work implicating innate immunity in ethanol-induced liver injury focuses primarily on long-term ethanol exposure. We investigated the early period of ethanol exposure to determine whether there were temporal associations between activation of innate immune responses and known correlates of liver injury. Female C57BL/6 mice were allowed free access to an ethanol-containing Lieber-DeCarli diet or were pair-fed a control diet. Within 4 days of ethanol exposure, we observed a striking spike in expression of hepatic proinflammatory cytokines-including tumor necrosis factor ␣ (TNF-␣), interleukin-6, and interferon-␥-prior to hepatic triglyceride accumulation or increased plasma alanine aminotransferase activities, as well as before the induction of cytochrome P450 2E1 or oxidative stress. This early spike in inflammatory cytokines coincided with deposition of C3b-iC3b/C3c (C3b) in the liver. This deposition, resulting from the cleavage of the third component of the complement system (C3), is evidence for activation of complement in response to ethanol. C3 ؊/؊ mice were protected from the early, ethanol-induced increase in hepatic TNF-␣ expression. Ethanol increased C3b deposition in mice deficient in C3a receptor or C5a receptor, as well as in wild-type mice depleted of hepatic macrophages; however, there was no increase in hepatic TNF-␣ in the absence of C3a receptor, C5a receptor, or hepatic macrophages. In contrast, the absence of Toll-like receptor 4 (TLR-4) had no effect on the early, ethanol-induced increase in either C3b or TNF-␣. Conclusion: We have identified a complement-and macrophage-dependent, but TLR-4 independent, phase in the pathogenesis of ethanol-induced liver injury. (HEPATOLOGY 2009;49:1326-1334

MIF, a multi-potent protein that exhibits both cytokine and chemotactic properties, is expressed by many cell types, including hepatocytes and non-parenchymal cells. We hypothesized that MIF is a key contributor to liver injury after ethanol exposure. Female C57BL/6 or MIF−/− mice were fed an ethanol-containing liquid diet or pair-fed control diet for 4 (11% total kcal; early response) or 25 (32% kcal; chronic response) days. Expression of MIF mRNA was induced at both 4d and 25d of ethanol feeding. After chronic ethanol, hepatic triglycerides and plasma ALT and AST were increased in wild-type, but not MIF−/−, mice. In order to understand the role of MIF in chronic ethanol-induced liver injury, we investigated the early response of wild-type and MIF−/− to ethanol. Ethanol feeding for 4d increased apoptosis of hepatic macrophages and activated complement in both wild-type and MIF−/− mice. However, TNFα expression was increased only in wild-type mice. This attenuation of TNF-α expression was associated with fewer F4/80+ macrophages in liver of MIF−/− mice. After 25d of ethanol feeding, chemokine expression was increased in wild-type mice, but not MIF−/− mice. Again, this protection was associated with decreased F4/80+ cells in MIF−/− mice after ethanol feeding. Chronic ethanol feeding also sensitized wild-type, but not MIF−/−, mice to lipopolysaccharide, increasing chemokine expression and monocyte recruitment into the liver. Conclusion Taken together, these data indicate that MIF is an important mediator in the regulation of chemokine production and immune cell infiltration in the liver during ethanol feeding and promotes ethanol-induced steatosis and hepatocyte damage.