Interaction with activated monocytes enhances cytokine expression and suppressive activity of human CD4+CD45ro+CD25+CD127low regulatory T cells

Objective Despite the high frequency of CD4+ T cells with a regulatory phenotype (CD25+CD127low FoxP3+) in the joints of patients with rheumatoid arthritis (RA), inflammation persists. One possible explanation is that human Treg cells are converted into proinflammatory interleukin-17 (IL-17)producing cells by inflammatory mediators and thereby lose their suppressive function. The aim of this study was to investigate whether activated monocytes, which are potent producers of inflammatory cytokines and are abundantly present in the rheumatic joint, induce proinflammatory cytokine expression in human Treg cells and impair their regulatory function. Methods The presence and phenotype of CD4+CD45RO+CD25+CD127low T cells (memory Treg cells) and CD14+ monocytes in the peripheral blood (PB) and synovial fluid (SF) of patients with RA were investigated by flow cytometry. Memory Treg cells obtained from healthy control subjects underwent fluorescence-activated cell sorting and then were cocultured with autologous activated monocytes and stimulated with anti-CD3 monoclonal antibodies. Intracellular cytokine expression, phenotype, and function of cells were determined by flow cytometry, enzyme-linked immunosorbent assay, and proliferation assays. Results In patients with RA, the frequencies of CD4+CD45RO+CD25+CD127low Treg cells and activated CD14+ monocytes were higher in SF compared with PB. In vitroactivated monocytes induced an increase in the percentage of IL-17positive, interferon- (IFN)positive, and tumor necrosis factor (TNF)positive Treg cells as well as IL-10positive Treg cells. The observed increase in IL-17positive and IFN-positive Treg cells was driven by monocyte-derived IL-1, IL-6, and TNF and was mediated by both CD14+CD16 and CD14+CD16+ monocyte subsets. Despite enhanced cytokine expression, cells maintained their CD25+FoxP3+CD39+ Treg cell phenotype and showed an enhanced capacity to suppress T cell proliferation and IL-17 production. Conclusion Treg cells exposed to a proinflammatory environment show increased cytokine expression as well as enhanced suppressive activity.