T-CELL SPECIFICITY IN IMMUNITY AND AUTOIMMUNITY TO DNA

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Antibodies to a variety of cellular antigens, mostly nuclear in origin, have been detected in sera from mice and humans with systemic lupus erythematosus. There is compelling evidence that these autoantibodies, particularly autoantibody to DNA, are responsible at least in part for the pathological manifestations of lupus. The immunological basis for the generation of anti-DNA autoantibody in mice and humans has been difficult to elucidate. Previous attempts to stimulate antibody with the same specificity for binding to DNA as anti-DNA antibody in lupus have been unsuccessful. This fact coupled with the presence of a generalized abnormality in lymphoid cell development in mouse models for lupus has led to the proposal that lupus autoantibodies arise by antigen independent, polyclonal B cell activation. However, recent results from our molecular analyses of the structure and ontogeny of autoimmune anti-DNA antibodies have indicated that autoimmunity to DNA is both initiated and sustained as a clonally selected, specific immune response to DNA or DNA complexes. The secondary-immune characteristics of autoimmune anti-DNA antibody implicates the participation of antigen-specific helper T cells in the generation of this autoantibody, and experimental data support this hypothesis. However, little is known about the specificity and function of such T cells. We have recently established an experimental immunization model for the induction of antibody to DNA in mice not genetically predisposed to autoimmune disease. The immunogen used in this experimental system is DNA in a complex with a DNA-binding peptide. The induced anti- DNA antibody has structural and specificity characteristics identical to those of autoimmune anti-DNA antibody in lupus. Moreover, mice producing this antibody develop symptoms of early stage lupus-nephritis. The research proposed in this application will exploit the new experimental immunization system to generate T cell clones and hybrids specific for DNA-binding peptides. T cell clones and hybrids will be generated from normal, nonautoimmune-prone and autoimmune-prone mice immunized with DNA-peptide complexes. These clones and hybrids will then be used to determine the specificity and function of helper T cells that can induce in vitro anti-DNA antibody production when stimulated with specific DNA-peptide. In particular these experiments will determine whether the MHC-restricted T cell epitope for such T cells is formed by the peptide alone or a combination of DNA and peptide. The experiments will also determine how changes in the amino acid sequence of specific peptides affect their recognition by specific T cells. T-cell receptor variable-region structures from T cells specific for different peptide- or DNA-peptide complexes will be compared with T-cell receptor variable- region structures from autoimmune T cells that stimulate in vitro anti-DNA antibody production.