I n multiple sclerosis (MS) patients who carry the Class II major histocompatibility (MHC) type HLA-DR2, T cells specific for amino acids 95-116 in the proteolipid protein (PLP) are activated and clonally expanded. However, it remains unclear whether these autoreactive T cells play a pathogenic role or, rather, protect against the central nervous system (CNS) damage. We have addressed this issue, using mice transgenic for the human MHC class II region carrying the HLA-DR2 (DRB1*1502) haplotype. After stimulating cultured lymph node cells repeatedly with PLP95-116, we generated 2 HLA-DR2–restricted, PLP95-116–specific T-cell lines (TCLs) from the transgenic mice immunized with this portion of PLP. The TCLs were CD4⁺ and produced T-helper 1 (Th1) cytokines in response to the peptide. These TCLs were adoptively transferred into RAG-2^–/– mice expressing HLA-DR2 (DRB1*1502) molecules. Mice receiving 1 of the TCLs developed a neurological disorder manifested ataxic movement without apparent paresis on day 3, 4, or 5 after cell transfer. Histological examination revealed inflammatory foci primarily restricted to the cerebrum and cerebellum, in association with scattered demyelinating lesions in the deep cerebral cortex. These results support a pathogenic role for PLP95-116–specific T cells in HLA-DR2⁺ MS patients, and shed light on the possible correlation between autoimmune target epitope and disease phenotype in human CNS autoimmune diseases.