Free radical mechanisms in immune reactions associated with alcoholic liver disease

Immune reactions toward the liver have been implicated in the pathogenesis of alcoholic liver disease (ALD), however the antigens involved are still poorly characterized. The contribution of free radical mechanisms to the immune reactions associated with ALD first emerged from the observation that the binding of hydroxyethyl free radicals (HER) to hepatic proteins, including cytochrome P4502E1 (CYP2E1), stimulates the production of specific antibodies in both alcohol-fed rats and alcoholic patients. We have subsequently observed that ALD patients have increased titers of antibodies directed against protein adducts with different lipid peroxidation products and antigens derived from the combination of malonildialdehyde and acetaldehyde. Free radical mechanisms can also contribute in promoting the autoimmune reactions often associated with ALD. Indeed, we have observed that antiphospholipid antibodies present in more than 50% of ALD patients recognize oxidized cardiolipin complexed with β₂-glycoprotein 1. Furthermore, a strict association between anti-HER IgG and the development of autoantibodies against CYP2E1 indicates that CYP2E1 modification by HER might promote anti-CYP2E1 autoreactivity in subjects with alcoholic cirrhosis. Altogether, these observations suggest the importance of ethanol-induced oxidative stress in stimulating immune reactions towards both liver allo-and self-antigens.