Immunogenetic analysis of anti-mitochondrial antibodies in primary biliary cirrhosis

Thomson, Richard Kerr (1999) Immunogenetic analysis of anti-mitochondrial antibodies in primary biliary cirrhosis. University of Southampton, Doctoral Thesis.

Abstract

The aims of this study were:

1. To isolate the specific autoantibody secreting B cells, by generating human anti-PDC-E2 monoclonal antibodies and precisely defining their specificities and functional properties.

2. To evaluate the immunoglubulin genes that encode these autoantibody structures, in order to explore the genetic basis of antigen recognition, and to further understand their origins in primary biliary cirrhosis.

Five heterohybridomas secreting PDC-E2 specific monoclonal antibodies, closely resembling the hallmark autoantibodies of PBC, were generated from the peripheral lymphocytes of two female patients.

Genetic analysis revealed no evidence of restricted immunoglobulin variable region gene usage, and therefore argued against the operation of a superantigen in the induction of antimitochondrial antibodies. Moreover, the pattern of heavy chain variable region (V_H) gene mutations suggested an antigen-driven selection of high affinity IgG autoantibodies, supporting a possible role for exogenous antigen in the pathogenesis of PBC. This may be an important determination of antigen recognition.

In further experiments, the precise structure-activity relationship of a single PDC-E2 specific monoclonal antibody (PD2) was explored. The results showed that antigen recognition required co-operative recognition by the heavy and light chains and that the heavy chain CDR3 was pivotal. Somatic mutations made only a slight difference to recognition of whole PDC. Reactivity to recombinant antigens, by contrast, was dramatically altered, resulting in a complete shift in antigen specificity from the E1/E3 binding domain to the inner lipoyl domain. This novel finding may be significant to the pathogenesis of primary biliary cirrhosis.

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