Structural and genetic characterisation of human autoantibodies encoded by the V4-34 gene

The project has been to elucidate the diverse means by which a subset of human autoantibodies interact with target antigen. By using monoclonal antibody technology and immunogenetics, the sites in the variable regions through which autoantibodies recognise red cell antigen, or DNA, have been delineated.Cold agglutinins are autoantibodies, usually of the IgM class, produced by B cell tumours, the majority of which bind to the Ii carbohydrate antigen on red blood cells at low temperatures. In 1986, we raised a monoclonal anti-idiotypic antibody, 9G4, which recognised all antibodies with this specificity. By using 6G4 it has been possible to identify, isolate and immortalise the tumour cells from twelve patients with cold agglutinin disease and to investigate the immunoglobulin (Ig) heavy and light chain gene usage. This analysis revealed that the same heavy chain gene, V4-34, was used to encode all the pathological IgMs. This apparently mandatory association of a single VH gene segment with an autoantibody activity is unprecedented in the human autoimmune response and suggested this interaction of antibody with antigen could be through the conserved framework region of the gene. Reactivity with red blood cells and with 9G4 was independent of the light chain gene used. Polyclonal cold agglutinins are also produced by normal B-cells in certain infections with organisms such as EBV and Mycoplasma pneumoniae. By establishing hybridomas from several EBV-infected patients we found that these antibodies were also encoded by the V4-34 gene.Further studies revealed that the 9G4 monoclonal antibody was specific for the products of V4-34 gene. We were therefore able to use this Ig marker (idiotope) to examine sera from patients with infections as well as with a wide range of autoimmune diseases. Significantly elevated levels of idiotope positive immunoglobulin were found in many patients with EBV and Mycoplasma infections and also in patients with systemic lupus erythematosus (SLE).