CD4 and rheumatoid arthritis: For example, the percentage and absolute number of Treg cells (CD4+CD25+/highCD127−/low) in the peripheral blood, synovial fluid, and synovial membranes are similar in RA patients and OA patients, and Treg cells in both cases show greater accumulation in the synovial fluid and synovial membranes than in the peripheral blood (77).