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 the cytochrome P450IID6. The aim of this study was to characterize the immunogenic sites on the P450IID6 molecule recognized by autoantibodies from individuals infected with the hepatitis C virus. Serum from 24 patients with markers of hepatitis C infection and liver/kidney microsome type 1 antibodies were tested by immunoblotting with human liver microsomal proteins. Eight of them with anti-P450IID6 antibodies were tested with synthetic peptides representing P450IID6 putative immunogenic 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 between aa 321 and 339 appears to represent the main antigenic site. Five out of eight anti-P450IID6 positive sera were also able to inhibit P450IID6 enzymatic activity in vitro at a dilution of 1:100. The anti-P450IID6 autoimmune response in chronic hepatitis C patients is polyclonal, probably inducible, and maintained by the liberation of P450IID6 by hepatocyte lysis. The characterization of the P450IID6 immunogenic site recognized by patients with hepatitis C infection may enable a specific test to be designed to identify those patients with autoimmune hepatitis type 2.