134 REACTIVITY TO NATIVE ASIALOGLYCOPROTEIN RECEPTOR AND ITS SUBUNITS IN AUTOIMMUNE LIVER DISEASE

Abstract

Asialoglycoprotein receptor (ASGPR) is a component of the hepatocyte membrane and the suggested target of tissue-damaging immune responses in autoimmune liver disease, nearly 90% of patients with autoimmune hepatitis having circulating autoantibodies against this receptor at titres that correlate closely with the histological severity of the disease. Native human ASGPR is a dimer or a trimer composed of two subunits: H1 of 46 kD and H2 of 50 kD with 60% homology. We have introduced the cDNAs of human ASGPR H1 and H2 subunits individually into NIH 3T3, a murine fibroblast cell line. Using a technique of indirect immunofluorescence, anti-native ASGPR antibodies demonstrated membrane expression of either subunit by UV-microscopy and cytofluorimetry. Immunoblot analysis also showed presence of the proteins in the cytoplasm of the transfected cells. We also assessed whether sera from patients with autoimmune liver disease react with the individually expressed ASGPR subunits and to what extent this reactivity is related to that against native ASGPR. Reactivity to H1 and H2 was investigated by indirect immunofluorescence and compared to that against native ASGPR assessed by radioimmunoassay (RIA). Sera from 20 patients, age range 4-20 yrs (median 12 yrs), with autoimmune liver disease (14 autoimmune hepatitis, 6 autoimmune sclerosing cholangitis) and 9 age matched healthy controls were tested. Anti-native ASGPR antibodies were detected in 11 patients (titre 1/200 - 1/2000 by RIA). Of these 11 sera, 2 were positive for anti-H1 antibodies alone, 3 were positive for both anti-H1 and anti-H2, and 6 showed no reaction. Of the 9 sera unreactive to native ASGPR, none reacted with the individual subunits. None of the 9 control sera reacted with H1 or H2 subunits or with the native ASGPR. The reactivity to native ASGPR was significantly correlated to that against subunits (p < 0.05). Our findings demonstrate that some epitopes target of autoimmunity are conserved when ASGPR is expressed in a monomeric form while others are present only on the full receptor.