Specificity of T cells in synovial fluid: high frequencies of CD8(+) T cells that are specific for certain viral epitopes

CD8(+) T cells dominate the lymphocyte population in synovial fluid in chro nic inflammatory arthritis. It is known that these CD8(+) T cells are often clonally or oligoclonally expanded, but their specificity and their releva nce to the pathogenesis of joint disease has remained unclear. We found tha t as many as 15.5% of synovial CD8(+) T cells may be specific for a single epitope from an Epstein-Barr virus lytic cycle protein. The virus-specific T cells within the joint showed increased expression of markers of activati on and differentiation compared with those in the periphery, and retained t heir functional capacity to secrete proinflammatory cytokines on stimulatio n. These activated, virus-specific CD8(+) T cells could therefore interact with synoviocytes, either by cell-cell contact or by a cytokine network, an d play a 'bystander' role in the maintenance of inflammation in patients wi th arthritis.