NUCLEOTIDE-SEQUENCE ANALYSIS OF NATURAL AND COMBINATORIAL ANTI-PDC-E2ANTIBODIES IN PATIENTS WITH PRIMARY BILIARY-CIRRHOSIS - RECAPITULATING IMMUNE SELECTION WITH MOLECULAR-BIOLOGY

We have analyzed at the nucleotide level the variable region gene sequ ences of five human mAbs and five recombinant Fab fragments derived fr om the mesenteric lymph nodes of patients with primary biliary cirrhos is. Both mAbs and Fabs were monospecific for dihydrolipoamide acetyltr ansferase, the E2 subunit of the pyruvate dehydrogenase complex, which has been shown to be the major autoantigen of primary biliary cirrhos is. We found that although the mAbs, mainly of the IgM isotype, were e ncoded by a diverse array of V-H and V-L gene segments either as direc t copies of germline genes or somatically mutated, the recombinant IgG Fabs expressed clonally related heavy chains displaying a high number of somatic mutations that very likely occurred in the context of Ag s election. Combinatorial pairing of clonally related heavy chains with highly homologous light chains suggests that the IgG anti-pyruvate deh ydrogenase complex repertoire of primary biliary cirrhosis patients is the result of the clonal expansion of a restricted set of B cells.