Identification of new autoantigens by protein array indicates a role for IL4 neutralization in Autoimmune Hepatitis

Autoimmune Hepatitis (AIH) is an unresolving inflammation of the liver of unknown cause. Diagnosis requires the exclusion of other conditions and the presence of characteristic features such as specific autoantibodies. Presently, these autoantibodies have relatively low sensitivity and specificity and are identified by immunostaining of cells or tissues, therefore there is a diagnostic need for better and easy to assess markers. To identify new AIH-specific autoantigens, we developed a protein microarray comprising 1626 human recombinant proteins, selected in silico for being secreted or membrane-associated. We screened sera from AIH patients on this microarray and compared their reactivity with sera from healthy donors and patients with chronic viral hepatitis C. We identified six human proteins that are specifically recognized by AIH sera. Serum reactivity to combination of these six autoantigens allows identification of AIH patients with high sensitivity (77%+/-4) and specificity (91%+/-8). Of the six autoantigens, the IL4 Receptor (CD124), which is expressed on the surface of both lymphocytes and hepatocytes, showed the highest individual sensitivity and specificity for AIH. Remarkably, sera of patients inhibited STAT6 phosphorylation induced by IL4 binding to CD124, demonstrating these autoantibodies are functional and suggesting IL4 neutralisation has a pathogenetic role in AIH.