Epitope mapping of cytochrome P4502D6 autoantigen in patients with chronichepatitis C during alpha-interferon treatment

Background/Aims: Cytochrome P450 2D6 (CYP2D6) has been documented as the ma jor target antigen of liver kidney microsomal autoantibodies type-1 (anti-L KM-1) in both autoimmune hepatitis type-2 (AIH-2) and hepatitis C (HCV). In HCV/anti-LKM-1-positive patients, the choice between alpha-interferon (alp ha-IFN) or immunosuppression may be difficult. This study was conducted to evaluate the course and outcome of alpha-IFN therapy in HCV/anti-LKM-1-posi tive and -negative patients and the alterations in these autoantibody titer s by the indirect immunofluorescence and a novel radioligand assay. Epitope mapping was also performed to screen for a potential shift in anti-LKM-1 b inding towards small linear epitopes, which are more often detected in AIH- 2 patients. Methods: Twenty-one patients with HCV infection received alpha-IFN. Seven p atients were anti-LKM-1 positive (study group) and 14 patients were anti-LK M-1 negative (disease control group). Anti-CYP2D6 detection was based on im munoprecipitation of [S-35]-methionine-labeled CYP2D6 recombinant protein ( rCYP2D6) produced by in vitro transcription/translation. Results: Four out of seven (57%) patients in the study group and 5/14 (36%) in the disease control group initially responded, but subsequently relapse d. During follow-up, alanine aminotransferase significantly increased in th e study group compared to the disease control group (p<0.01). A slight incr ease, followed by a plateau of autoantibody titers was recorded by the radi oligand assay and by indirect immunofluorescence during therapy and follow- up in most cases. In one patient, however, gamma-globulins and anti-LKM-1 t iters increased, reaching very high levels (1:40 960), (alpha-IFN was inter rupted and immunosuppression was started. HCV/anti-CYP2D6 positive sera rec ognized CYP2D6 expressed in E. coli and two truncated proteins (aa 250-494 and 321-494), Two out of seven sera, in addition reacted with a small linea r epitope of aa 257-269 tone of which also reacted with a C-terminal domain of aa 350-494). Conclusions: A rather mild deterioration in liver disease was observed in o nly 1/7 HCV/anti-LKM-1-positive patients during alpha-IFN treatment. This p atient showed high anti-CYPtD6 titers before the initiation of therapy, a s harp increase in anti-LKM-1 titers during treatment, and reactivities to a small linear epitope and an infrequently recognized C-terminal domain of CY P2D6, After switching to immunosuppressive treatment, a complete and sustai ned response was recorded. Further prospective studies from many centers ar e needed to define whether these features have general, clinical significan ce or not.