STUDY OF THE B-CELL RESPONSE TO CYTOCHROME P450IID6 IN SERA FROM CHRONIC HEPATITIS-C PATIENTS

Some patients with chronic hepatitis C develop liver/kidney microsome type 1 antibodies. Some of these autoantibodies are directed against t he cytochrome P450IID6. The aim of this study was to characterize the immunogenic sites on the P450IID6 molecule recognized by autoantibodie s from individuals infected with the hepatitis C virus. Serum from 24 patients with markers of hepatitis C infection and liver/kidney micros ome type I antibodies were tested by immunoblotting with human liver m icrosomal proteins. Eight of them with anti-P450IID6 antibodies were t ested with synthetic peptides representing P450IID6 putative immunogen ic sites and for their capacity to inhibit in vitro P450IID6 enzymatic activity. Anti-P450IID6 antibodies in the sera of chronic hepatitis C patients were of IgG subclass 1 and in one patient also of IgM type. These sera recognized different P450IID6 peptide sequences consisting of amino acids (aa) 200-214 and aa 271-339. The synthetic peptide betw een aa 321 and 339 appears to represent the main antigenic site. Five out of eight anti-P450IID6 positive sera were also able to inhibit P45 0IID6 enzymatic activity in vitro at a dilution of 1:100. The anti-P45 0IID6 autoimmune response in chronic hepatitis C patients is polyclona l, probably inducible, and maintained by the liberation of P450IID6 by hepatocyte lysis. The characterization of the P450IID6 immunogenic si te recognized by patients with hepatitis C infection may enable a spec ific test to be designed to identify those patients with autoimmune he patitis type 2.