Predominance of mononuclear cells expressing the chemokine receptor CCR5 in synovial effusions of patients with different forms of arthritis

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Abstract
Objective To study the role of the chemokine receptors CCR5 and CCR2 in patients with arthritis. Methods CCR5 expression on peripheral blood leukocytes was compared with the expression on leukocytes isolated from the synovial fluid of 20 patients with different rheumatic joint diseases. Three additional samples were studied for CCR2 expression. The expression of chemokine receptors on blood and synovial fluid leukocytes was determined by 3‐color flow cytometry analysis. To test CCR5 receptor down‐modulation from the cell surface, leukocytes were incubated in vitro with a RANTES (regulated on activation, normal T cell expressed and secreted) derivative, aminooxypentane (AOP)–RANTES. Patients were genotyped for the Δ32 CCR5 deletion by polymerase chain reaction. Results A high percentage of CCR5‐expressing CD4+ and CD8+ T cells (74% and 81%, respectively), monocytes (51%), and natural killer cells (35%) was found in the synovial fluid of all patients, whereas in the peripheral blood, only a small percentage of these cells expressed CCR5 (13%, 32%, 7.8%, and 4%, respectively). Infiltration of CCR5‐positive leukocytes was not reduced in CCR5‐heterozygous patients. A similar, but less pronounced, distribution was observed for CCR2‐positive T cells. In vitro, CCR5 was completely down‐modulated on synovial fluid leukocytes by AOP‐RANTES. Conclusion The predominance of CCR5‐positive mononuclear cells in the synovial effusions of patients with arthritis suggests an important role for CCR5 in the process of joint inflammation, and identifies CCR5 as a possible new target for therapeutic intervention.