Nuclear autoantigens in patients with SLE or related diseases are generally constituents of large particles. The quaternary structure of a multiprotein complex is a crucial determinant of antigen presentation to T cells, and altering the quaternary structure of a complex could activate autoreactive T cells specific for minor T cell determinants. The binding of autoantibodies to self antigens might similarly activate autoreactive T cells by altering antigen conformation and processing. In preliminary studies, we have identified a murine hybridoma (designated 1140) that secretes an IgM ANA reactive with a 350 kDa DNA-dependent protein kinase (DNA-PK) physically associated with the Ku autoantigen. Injection of the hybridoma into BALB/c mice induced IgG autoantibodies characteristic of SLE, including autoantibodies to the 100 kDa Su autoantigen, the 33 kDa U1-RNP A protein, and an unidentified 70 kDa autoantigen. The induction of IgG autoantibodies characteristic of SLE in nonautoimmune mice by 1140 was of considerable interest in view of biochemical evidence that the Su and 70 kDa antigens are physically associated with DNA-PK in the cell. We hypothesize that 1140 binds to a multiprotein complex consisting of DNA- PK, Ku, Su, and other proteins, inducing a conformational change that leads to more efficient presentation of a self peptide to which the mice are not tolerant. Autoreactive T, cells specific for this minor determinant may induce ANAs to other components of the complex that alter autoantigen processing further, inducing additional autoreactive T cells and ANAs. A similar phenomenon may occur in some patients with monoclonal gammopathies such as a patient with a B cell lymphoma producing a paraprotein specific for DNA-PK. The autoantibodies to Ku detected in the patient's serum along with the monoclonal anti-DNA-PK may have been induced by a mechanism analogous to that in the 1140 model. The proposed studies will examine the mechanism of ANA induction by 1140.
In Specific Aim 1, DNA-PK and the 100, 70, and 33 kDa autoantigens targeted by autoantibodies induced by 1140 will characterized biochemically, and cDNA clones encoding DNA-PK and other autoantigens will be obtained and expressed in bacteria.
In Specific Aim 2, the possible role of 1140- autoantigen immune complexes in triggering autoimmunity will be assessed.
Specific Aim 3 will investigate whether 1140 induces the production of autoreactive T cells specific for DNA-PK or other autoantigens. Alternative models that might explain autoantibody induction by 1140 and the human paraprotein, including an idiotype-antiidiotype mechanism will also be examined. These studies may define a novel positive feedback mechanism of ANA regulation that causes """"""""spreading"""""""" of autoimmunity in patients with SLE and monoclonal gammopathies.
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