CD26 Surface Molecule Involvement in T Cell Activation and Lymphokine Synthesis in Rheumatoid and Other Inflammatory Synovitis

T cell surface expression and the functional role of CD26 antigen (Ag), a surface ectoenzyme involved in T cell activation and migration across the extracellular matrix, were analyzed in the peripheral blood (PB) and synovial fluid (SF) from patients with inflammatory arthritides. CD26 membrane expression on T cells was detected by cytofluorometry using two different monoclonal antibodies, anti-Ta1 and anti-1F7, while cell proliferation and both IL-2 and IFN-γ production were evaluated in anti-CD3- or anti-CD2-stimulated cell cultures after Ag surface modulation with anti-1F7. The results showed that Ta1 and 1F7 Ag expression were increased on T cells from PB of patients with active, but not inactive, rheumatoid arthritis (RA). Most SF T cells from RA or other inflammatory arthritides displayed the memory marker CD45R0 and the Ta1 Ag, but lacked the 1F7 molecule. In addition,in vitro1F7 modulation, which enhanced RA PB T cell proliferation and both IL-2 and IFN-γ synthesis, did not synergize with anti-CD3 or anti-CD2 in inducing IL-2-dependent activation of SF T cells, but reduced IFN-γ production. A spontaneous reappearance of 1F7 Ag on the SF T cell surface was seen after 2–5 days in culture. Phorbol myristate acetate, able to accelerate its reexpression, also restored a normal response of SF T cells to anti-1F7 comitogenic effects. These data confirm a role of the CD26 surface molecule in regulating T cell activation and lymphokine synthesis. This observation may have important implications in the regulation of T cell activity at the joint level during chronic inflammatory processes.