Immunoreactivity of recombinant human oxo-glutarate dehydrogenase complex (OGDC)-E2 protein in primary biliary cirrhosis

Abstract

The E2 component of the oxo-glutarate dehydrogenase complex (OGDC), which is a member of the 2-oxo acid dehydrogenase multienzyme complex (2-ODC) family, is one of the autoantigens eliciting anti-mitochondrial antibodies in primary biliary cirrhosis (PBC). In this study, the author investigated the specific reactivity of recombinant human OGDC-E2 protein with sera from patients with PBC. Using the amplified cDNA of HeLa cells as a template, OGDC-E2 cDNA (258 bp), including the inner lipoyl-binding domain which constitutes the major epitope in OGDC-E2, was amplified by polymerase chain reaction (PCR). This product was inserted into the pET28 vector digested with NcoI and XhoI, resulting in a plasmid which allowed the expression of the recombinant protein in Escherichia coli. Using this recombinant protein as the antigen, an enzyme-linked immunosorbent assay (ELISA) for anti-OGDC-E2 antibody was developed. The antigen-specific reactivity was confirmed by inhibition tests. No sera from normal controls or patients with chronic liver diseases other than PBC reacted with the recombinant OGDC-E2. In contrast, 24% of the sera from 136 patients with PBC reacted with the recombinant OGDC-E2, and the reactivity was independent of other 2-oxo acid dehydrogenase complexes, i.e. pyruvate dehydrogenase complex (PDC)-E2 and branched chain 2-oxo acid dehydrogenase complex (BCOADC)-E2. Specific reactivity with OGDC-E2 alone was found in four of 15 anti-mitochondrial antibody (AMA)-negative patients with PBC.