Resting CD4+ effector memory T cells are precursors of bystander-activated effectors:: a surrogate model of rheumatoid arthritis synovial T-cell function

Background Previously we described a system whereby human peripheral blood T cells stimulated for 8 days in a cytokine cocktail acquired effector function for contact-dependent induction of proinflammatory cytokines from monocytes. We termed these cells cytokine-activated (Tck) cells and found that the signalling pathways elicited in the responding monocytes were identical whether they were placed in contact with Tck cells or with T cells isolated from rheumatoid arthritis (RA) synovial tissue. Methods Here, using magnetic beads and fluorescence-activated cell sorting, we extensively phenotype the Tck effector cells and conclude that effector function resides within the CD4(+)CD45RO(+), CCR7(-), CD49d(high) population, and that these cells are derived from the effector memory CD4(+) T cells in resting blood. Results After stimulation in culture, these cells produce a wide range of T-cell cytokines, undergo proliferation and differentiate to acquire an extensively activated phenotype resembling RA synovial T cells. Blocking antibodies against CD69, CD18, or CD49d resulted in a reduction of tumour necrosis factor-alpha production from monocytes stimulated with CD4(+)CD45RO(+) Tck cells in the co-culture assay. Moreover, blockade of these ligands also resulted in inhibition of spontaneous tumour necrosis factor-alpha production in RA synovial mononuclear cell cultures. Conclusion Taken together, these data strengthen our understanding of T-cell effector function, highlight the multiple involvement of different cell surface ligands in cell-cell contact and, provide novel insights into the pathogenesis of inflammatory RA disease.