Detection and epitope analysis of autoantigen-reactive T cells to the U1-small nuclear ribonucleoprotein A protein in autoimmune disease patients.

T cells that recognize autoantigens might play an important role in autoimmune diseases. To analyze "autoantigen-reactive T cell" in patients with an autoimmune disease, a human lymphocyte proliferation assay using soluble recombinant autoantigens has been conducted. PBMC from mixed connective tissue disease and SLE patients who possessed anti-U1-small nuclear ribonucleoprotein (snRNP) A autoantibodies responded to a recombinant U1-snRNP A protein. In contrast, PBMC from healthy subjects or autoimmune disease patients not possessing anti-U1-snRNP A autoantibodies did not show such responses. In addition, this proliferative response was inhibited by anti-CD4 mAb. Limiting dilution analyses revealed that the autoantigen-reactive T cells exist in relatively high frequency (1 of 4,065 to 1 of 23,256) in the mixed connective tissue disease patients. Moreover, by T cell epitope mapping, the T cell epitope area was found to be located in the C-terminus of the U1-snRNP A protein, overlapping the B cell epitope area that has been reported. These findings suggest the presence of autoantigen-reactive T cells in such patients, and when these T cells are activated, they may play a central role in the autoantibody generation.