In the nonobese diabetic mouse, a predominant component of the autoreactive CD4+ T cell repertoire is directed against the B: 9-23 segment of the insulin B chain. Previous studies established that the majority of insulin-reactive T cells specifically recognize a weak peptide-MHC binding register within the B: 9-23 segment, that to the 12–20 register. These T cells are uniquely stimulated when the B: 9-23 peptide, but not the insulin protein, is offered to antigen presenting cells (APCs). Here, we report on a T cell receptor (TCR) transgenic mouse (8F10) that offers important new insights into the biology of these unconventional T cells. Many of the 8F10 CD4+ T cells escaped negative selection and were highly pathogenic. The T cells were directly recruited into islets of Langerhans, where they established contact with resident intra-islet APCs. Immunogenic insulin had to be presented in order for the T cells to localize and cause disease. These T cells bypassed an initial priming stage in the pancreatic lymph node thought to precede islet T cell entry. 8F10 T cells induced the production of antiinsulin antibodies and islets contained immunoglobulin (IgG) deposited on ß cells and along the vessel walls.

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