Autoimmune-prone nonobese diabetic mice deficient for B7-2 spontaneously develop an autoimmune peripheral neuropathy mediated by inflammatory CD4(+) T cells that is reminiscent of Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy. To determine the etiology of this disease, CD4(+) T cell hybridomas were generated from inflamed tissue-derived CD4(+) T cells. A majority of T cell hybridomas were specific for myelin protein 0 (P0), which was the principal target of autoantibody responses targeting nerve proteins. To determine whether P0-specific T cell responses were sufficient to mediate disease, we generated a novel myelin P0-specific T cell receptor transgenic (POT) mouse. POT T cells were not tolerized or deleted during thymic development and proliferated in response to P0 in vitro. Importantly, when bred onto a recombination activating gene knockout background, POT mice developed a fulminant form of peripheral neuropathy that affected all mice by weaning age and led to their premature death by 3-5 wk of age. This abrupt disease was associated with the production of interferon gamma by P0-specific T cells and a lack of CD4(+) Foxp3(+) regulatory T cells. Collectively, our data suggest that myelin P0 is a major autoantigen in autoimmune peripheral neuropathy.