A new approach to cytochrome CYP2D6 antibody detection in autoimmune hepatitis type‐2 (AIH‐2) and chronic hepatitis C virus (HCV) infection: a sensitive and quantitative radioligand assay

Antibodies specific for cytochrome CYP2D6, formally known as liver‐kidney‐microsome type‐1 antibodies (LKM‐1), are characteristically found in a subgroup of patients presenting autoimmune hepatitis. They are also found in some patients with chronic HCV infection. These autoantibodies are usually detected by indirect immunofluorescence, immunoblotting and ELISA tests. In an attempt to set up a more sensitive detection assay we developed a quantitative immunoprecipitation radioligand assay using a 35S‐methionine‐labelled CYP2D6 antigen obtained by in vitro transcription and translation synthesis. All 16 sera from AIH‐2 patients strongly bound to this CYP2D6 antigen. Two of the nine sera (22%) from AIH‐2 patients that presented only liver cytosol‐1 antibodies also bound to CYP2D6. All 24 sera from HCV patients that were positive for LKM‐1 antibodies by indirect immunofluorescence were also positive using this CYP2D6 radioligand assay. Lastly, all 15 sera from HCV patients negative for LKM‐1 antibodies were negative by this test. The present results support the view that this quantitative radioligand assay is more sensitive than immunoblotting and ELISA CYP2D6 assays, and that it could be used in combination with indirect immunofluorescence assay.