Establishment and structural analysis of human mAb to the E2 component of the 2-oxoglutarate dehydrogenase complex generated from a patient with primary biliary cirrhosis.

We established one Epstein-Barr virus-transformed B cell hybrid clone producing human mAb of the IgG class to the 2-oxoglutarate dehydrogenase complex (OGDC) for the first time from the peripheral B lymphocytes of a patient with primary biliary cirrhosis (PBC). This mAb, designated mAbM37GO37, specifically bound to OGDC and its dissociation constant with OGDC was calculated to be 3.70 x 10(-10) mol/l. mAbM37GO37 stained murine stomach/kidney cryostat sections in a typical immunofluorescence pattern of antimitochondrial antibody (AMA). Western blotting analysis revealed that mAbM37GO37 reacted with an E2 component of OGDC but not with other components of OGDC nor pyruvate dehydrogenase complex (PDC). Furthermore, mAbM37GO37 completely inhibited the enzymatic activity of OGDC. In order to determine the structure and genetic origin of anti-OGDC autoantibody, we cloned and sequenced the Ig heavy and light chain variable regions of mAbM37GO37. This mAb used the VHIII family member, V3-7, and the V kappa IV family member. The amino acid difference between the expressed V genes of this mAb and respective putative germline genes was concentrated within the complementarity determining regions (CDR) rather than the framework regions (FR). The R:S mutation ratio was high in the CDR and low in the FR. These features suggested that the immune response to OGDC is similar to that to exogenous antigen, and that the heavy and light chain variable regions of the anti-OGDC antibody undergo somatic hypermutation through antigen-driven clonal selection. This human mAb to OGDC, which was established for the first time from a patient with PBC and characterized at the molecular level, would be a valuable tool to study the B cell autoepitopes of OGDC, to clone as yet undetermined full length cDNA encoding OGDC and to dissect the autoimmune response to mitochondrial antigens in PBC.