THU0038 Cytokine and growth factor regulation of ra and oa synovial macrophage differentiation into osteoclasts and dendritic cells
Authors: L Danks, NA Athanasou
Journal: Annals of the Rheumatic Diseases (2001)

<h3>Background</h3> Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease in which an unknown autoantigen is presented to T cells. In RA synovial tissue, fully differentiated dendritic cells (DC) are found in close association with T cells. DC are thought to be the major antigen presenting cells in RA. It has previously been shown that human monocytes differentiate into DC when stimulated with GM-CSF and IL-4 with terminal differentiation promoted by TNFa. We have shown that circulating monocytes and synovial macrophages are stimulated to differentiate into functional osteoclasts in the presence of RANKL, M-CSF and dexamethasone (Dex). <h3>Objectives</h3> We aimed to determine whether synovial macrophages preferentially differentiate into DC or functional osteoclasts in the presence of specific combinations of cytokines/growth factors which are known to be involved in the pathogenesis of RA and other inflammatory bone conditions. <h3>Methods</h3> Synovial macrophages were isolated from the knee and hip of RA and OA patients. The cells were seeded onto dentine slices and coverslips and cultured for 1, 7 and 14 days in the presence/absence of different combinations of the following factors: RANKL (30 ng/ml), Dex (10–8M), MCSF (0–50 ng/ml), GM-CSF (0–50 ng/ml), IL-4 (10 ng/ml), TNFa (10 ng/ml). Macrophage-osteoclast differentiation was quantified by counting the number of multinucleated, tartrate-resistant acid phosphatase (TRAP) cells present, and by measuring their ability to carry out lacunar resorption on dentine slices. Mature DC were identified by the expression of the marker CD83. <h3>Results</h3> In the presence of RANKL, M-CSF and Dex, RA and OA synovial macrophages were maximally stimulated to form osteoclasts; a few cells in these cultures were CD83 positive. The majority were TRAP positive and capable of forming resorption pits on dentine. GM-CSF, IL-4 and TNFa stimulated maximum expression of the mature DC marker CD83 in the cultures; these cultures were TRAP negative and incapable of resorbing dentine. Synovial macrophages cultured in the presence of RANKL and GM-CSF alone resulted in the formation of large multinucleated cells which expressed the marker CD83; a few of these large multinucleated cells were also TRAP positive. Cell cultures treated with GM-CSF were capable of significantly less dentine resorption than cultures treated with RANKL and M-CSF. The addition of RANKL did not modify CD83 expression in any of the above cytokine/growth factor combinations. The presence of Dex significantly inhibited the expression of this DC marker in all cultures. <h3>Conclusion</h3> This study demonstrates that synovial tissue macrophages have the capacity to differentiate into either functional osteoclasts or mature dendritic cells depending on the presence or absence of specific humoral factors. <h3>References</h3> Peters JH, Gieseler R, Thiele B, Steinbach F. Dendritic cells: from ontogenetic orphans to myelomonocytic decendants. Immunol Today 1996;17(6):273–8 Highton J, Kean A, Hessian PA, Thomson J, Rietveld J, Hart D. Cells expressing dendritic cell markers are present in the rheumatoid nodule. J Rheumatol. 2000;27(2):339–46 Thomas R, MacDonald KP, Petit AR, Cavanagh LL, Padmanabha J, Zehntner S. Dendritic cells and the pathogenesis of rheumatoid arthritis. J Leukoc Biol. 1999;66(2):286–92