Systemic lupus erythematosus (SLE) is an autoimmune disease characterized, in part, by the production of antinuclear antibodies, which appear to play a role in the pathogenesis of the disease. The origin of antinuclear antibodies in SLE is unknown, but there is increasing evidence that their production by B cells is driven by antigen. While there is considerable indirect evidence that T cells are also involved in this process, T cells reacting with nuclear autoantigens have never been demonstrated convincingly. We previously characterized a DNA-binding protein complex termed p7O/p8O (Ku) which is one of the targets of antinuclear antibodies in SLE. Like most lupus autoantigens, Ku is a large macromolecular complex, and antibodies to each component of the complex are generated simultaneously. We hypothesize that the """"""""linked"""""""" production of autoantibodies to p7O, p8O, and DNA might result from T cells reacting with a single component of the Ku complex which provide help for B cells specific for other components (""""""""intermolecular help""""""""). Our recent observation that Ku forms complexes with viral proteins in EpsteinBarr virus and adenovirus infected cells raises the possibility that T cells reacting with viral polypeptides complexed to Ku might provide intermolecular help for Ku autoantibody production. To test the intermolecular help hypothesis, we will first characterize B cell epitopes of Ku using monoclonal antibodies (MAb) to conformational or discontinuous epitopes, and mutant Ku antigens expressed in mammalian cells or bacteria. These studies are a direct extension of our previous work. Second, the viral and cellular proteins complexed to Ku in EBV and adenovirus infected cells will be identified by coimmunoprecipitation from sucrose gradients using Ku MAb, followed by their purification and N-terminal amino acid sequencing. Finally, T-B cell interactions involved in generating antibodies to Ku complexes will be examined in mice. In particular, the role on intermolecular help in producing antibodies to Ku will be tested in murine models to assess whether antiviral T cells might provide help to B cells specific for p7O, p8O, or DNA. Subsequent exploratory studies will be aimed at extending the findings in mice to human autoimmune diseases.
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