Immune response against protein epitopes modified with acetaldehyde and its clinical significance in alcoholoic liver diseases

Acetaldehyde, the first metabolite of ethanol, is capable to bind various proteins followed by the formation of acetaldehyde adducts. This condensate is supposed to act as a neoantigen. We have recently demonstrated the appearance of acetaldehyde adducts in liver of experimental animals after chronic ethanol treatment, and we produced an experimental hepatitis in guinea pig by immunization with acetaldehyde adducts and treatment with free access to ethanol. However the structure of acetaldehyde adducts and its characteristics are still vague. To elucidate the binding site of anti-adducts antibody against the epitope on adducts, we established a cell line of hybridoma producing monoclonal antibody. This monoclonal antibody recognized condensate modified with high concentration of acetaldehyde (1-10 mM) but not those modified with low concentration of it (20-200 μM), whereas the polyclonal antibody produced by conventional method recognized both of them. Using the affinity-purified adducts by monoclonal or polyclonal antibody-liganded column, we examined the antibody titeres by ELISA. The elevation of antibody titer was more specific in chronic alcoholics, especially in patients with hepatic inflammatory change, when antibody was measured against the adducts purified by monoclonal antibody than against the adduct purified by polyclonal antibody. Namely, there exist different types of antibody according to the concentration of acetaldehyde to form the adducts. The concentration of acetaldehyde is thought to be much greater in the liver of alcoholics compared to the patient with non alcoholic liver disease. Actually we have immunohistochemically detected the adduct related to high concentration of acetaldehyde in the liver specimens of alcoholics. In conclusion, the appearance of adduct related to high concentration of acetaldehyde and the acquisition of immunity against it appear to be a characteristic feature in alcoholics with hepatic inflammation. Therefore, evaluation of circulating antibodies against protein epitope related to high concentration of acetaldehyde is helpful to know conditions of such types of liver disease seen in alcoholics.