Epitope mapping of cytochrome P4502D6 autoantigen in patients with chronic hepatitis C during alpha-interferon treatment.
OBJECTIVE
Cytochrome P450 2D6 (CYP2D6) has been documented as the major target antigen of liver kidney microsomal autoantibodies type-1 (anti-LKM-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 (alpha-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-positive and -negative patients and the alterations in these autoantibody titers by the indirect immunofluorescence and a novel radioligand assay. Epitope mapping was also performed to screen for a potential shift in anti-LKM-1 binding towards small linear epitopes, which are more often detected in AIH-2 patients.


METHODS
Twenty-one patients with HCV infection received alpha-IFN. Seven patients were anti-LKM-1 positive (study group) and 14 patients were anti-LKM-1 negative (disease control group). Anti-CYP2D6 detection was based on immunoprecipitation of [35S]-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 relapsed. During follow-up, alanine aminotransferase significantly increased in the study group compared to the disease control group (p<0.01). A slight increase, followed by a plateau of autoantibody titers was recorded by the radioligand assay and by indirect immunofluorescence during therapy and follow-up in most cases. In one patient, however, gamma-globulins and anti-LKM-1 titers increased, reaching very high levels (1:40 960). alpha-IFN was interrupted and immunosuppression was started. HCV/anti-CYP2D6 positive sera recognized 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 linear epitope of aa 257-269 (one of which also reacted with a C-terminal domain of aa 350-494).


CONCLUSIONS
A rather mild deterioration in liver disease was observed in only 1/7 HCV/anti-LKM-1-positive patients during alpha-IFN treatment. This patient showed high anti-CYP2D6 titers before the initiation of therapy, a sharp increase in anti-LKM-1 titers during treatment, and reactivities to a small linear epitope and an infrequently recognized C-terminal domain of CYP2D6. After switching to immunosuppressive treatment, a complete and sustained response was recorded. Further prospective studies from many centers are needed to define whether these features have general, clinical significance or not.
Dalekos
G N
GN
Department of Gastroenterology and Hepatology, Medizinische Hochschule Hannover, Germany.
Wedemeyer
H
H
Obermayer-Straub
P
P
Kayser
A
A
Barut
A
A
Frank
H
H
Manns
M P
MP
D000293:Adolescent; D000328:Adult; D000998:Antiviral Agents / Q000276:immunology / Q000627:therapeutic use*; D001324:Autoantigens / Q000276:immunology*; D019389:Cytochrome P-450 CYP2D6 / Q000276:immunology*; D018604:Epitope Mapping; D005260:Female; D019698:Hepatitis C, Chronic / Q000188:drug therapy / Q000276:immunology*; D006801:Humans; D007165:Immunosuppression Therapy; D016898:Interferon-alpha / Q000276:immunology / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged
D000998:Antiviral Agents; D001324:Autoantigens; D016898:Interferon-alpha; D019389:Cytochrome P-450 CYP2D6