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Demonstration of PDC‐E1 subunits as major antigens in the complement‐fixing fraction M4 and re‐evaluation of PDC‐E1‐specific antibodies in PBC patients
Author(s) -
Berg Christoph P.,
Stein Gerburg M.,
Klein Reinhild,
Pascu Maria,
Berg Thomas,
Kammer Winfried,
Priemer Martin,
Nordheim Alfred,
SchulzeOsthoff Klaus,
Gregor Michael,
Wesselborg Sebastian,
Berg Peter A.
Publication year - 2006
Publication title -
liver international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.873
H-Index - 110
eISSN - 1478-3231
pISSN - 1478-3223
DOI - 10.1111/j.1478-3231.2006.01303.x
Subject(s) - antibody , complement (music) , antigen , protein subunit , fraction (chemistry) , computational biology , chemistry , biology , immunology , biochemistry , gene , phenotype , chromatography , complementation
Background: Primary biliary cirrhosis (PBC) is characterized by the presence of antimitochondrial antibodies (AMA). Autoantibodies specific for the mitochondrial M4 antigen can be detected by a complement fixation test (CFT) but not by immunoblotting. The aim of this study was to elucidate the identity of the M4 antigen. Patients and methods: M4 proteins were purified by affinity chromatography using IgG fractions of PBC marker sera being CFT positive ( n =5) or negative ( n =5) and identified by Western blotting, silver staining and sequence analysis. Further, a cohort of 57 PBC patients was tested for the reactivity to M4 and pyruvate dehydrogenase complex (PDC). Results: Two AMA patterns of the marker sera were visualized: CFT‐positive sera were defined as PDC‐E2 + /E1 + and the CFT‐negative sera as PDC‐E2 + /E1 − . The major proteins in the M4 fraction could be related to the PDC‐E1 subunits. A clear‐cut association between anti‐M4 reactivity in the CFT and the reactivity to both PDC subunits could also be documented in the cohort of 57 PBC patients showing anti‐PDC‐E1α and E1β antibodies at a frequency of 74% and 67%. Conclusions: CFT reactivity against M4 antigens could be preferentially identified as a reaction against PDC‐E1. As PDC‐E1 subunits as compared with PDC‐E2 lack lipoyl‐binding sites, they probably have to be considered as an independent and important target.