TIENILIC ACID-INDUCED AUTOIMMUNE HEPATITIS - ANTI-LIVER AND ANTI-KIDNEY MICROSOMAL TYPE-2 AUTOANTIBODIES RECOGNIZE A 3-SITE CONFORMATIONAL EPITOPE ON CYTOCHROME-P4502C9

Tienilic acid-induced hepatitis is characterized by the presence of an ti-liver and -kidney microsomal (anti-LKM2) autoantibodies in patient sera. Cytochrome P4502C9 (CYP2C9), involved in the metabolism of tieni lic acid, was shown to be a target for tienilic acid-reactive metaboli tes and for autoantibodies. To further investigate the relationship be tween drug metabolism and the pathogenesis of this drug-induced autoim mune disease, the specificity of anti-LKM2 autoantibodies toward CYP2C 9 was first determined, and the antigenic sites on CYP2C9 were localiz ed. By constructing several deletion mutants derived from CYP2C9 cDNA and by probing the corresponding proteins with different anti-LKM2 ser a, we defined three regions (amino acids 314-322, 345-356, and 439-455 ); they interacted to form a major conformational autoantibody binding site. This binding site was immunoreactive with 100% of sera and allo wed removal of the entire reactivity of the sera tested by immunoblott ing. Epitope mapping studies have been performed for CYP2D6, CYP17, CY P21A2, and, recently, CYP3A. Those data were compared with the results obtained in the current study with CYP2C9 in an attempt to elucidate one of the mechanisms by which CYP becomes immunogenic.