AbstractObjectivePreviously, we showed that 15‐20% of patients with rheumatoid arthritis (RA) have oligoclonal expansions of peripheral blood CD8+ T cells expressing T cell receptors encoded by the Vα12 (AV12S1) gene. To better understand the significance of these expansions, the present study was undertaken to determine their specificity.MethodsWe cloned and characterized Vα12+,CD8+ T cells from the peripheral blood of 1 RA patient with a clonal expansion of these T cells.ResultsThe T cell clones were autoreactive since they recognized autologous, but not allogeneic, antigen‐presenting cells. Upon activation, these T cells secreted interleukin‐4 and interleukin‐10. The autoreactive T cell clones were class I major histocompatibility complex (MHC) restricted, by either HLA‐B60 or HLA‐Cw3.ConclusionA large population of class I MHC‐restricted CD8+ T cells in a patient with RA is clonally expanded and autoreactive. These cells define a novel immune aberration in RA and provide a tool for defining the autoantigens that activate expanded T cell popu
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