Objective: To study CD69+ synovial fluid (SF) T cells and the mechanisms regulating CD69 expression in rheumatoid arthritis (RA).
Methods: One or 2 color flow cytometry was used to determine CD69 and other surface markers. Cultures of SF T cells alone or mixed with autologous SF non-T cells were used for CD69 maintenance assays.
Results: SF T cells were enriched in CD69+. These cells were mainly CD3+, CD8+ and CD25-. CD69 was maintained on SF T cells cultured with SF non-T cells but not when the former were cultured alone or in the presence of different supernatants from RA SF T and non-T cells cultures with sustained CD69 expression. Pretreatment of T and non-T cells with anti-CD18 monoclonal antibody inhibited CD69 expression, while paraformaldehyde-"fixed" non-T cells effectively maintained it.
Conclusion: SF T cells exhibit a phenotype with evidence of past and recent activation. Our studies demonstrate that most of the recently activated SF T cells are CD8+. We also found that continuous cell-to-cell interaction between T and non-T cells are responsible for the maintenance of this particular state of activation of SF T cells.