Generation mechanism of RANKL+ effector memory B cells: relevance to the pathogenesis of rheumatoid arthritis
BackgroundThe efficacy of B cell depleting therapies for rheumatoid arthritis underscores antibody independent functions of effector B cells such as cognate T B interactions and production of pro inflammatory cytokines. Receptor activator of nuclear factor kB ligand (RANKL) is a key cytokine involved in bone destruction and is highly expressed in synovial fluid B cells in patients with rheumatoid arthritis. In this study we sought to clarify the generation mechanism of RANKL+ effector B cells and their impacts on osteoclast differentiation.MethodsPeripheral blood and synovial fluid B cells from healthy controls and patients with rheumatoid arthritis were isolated using cell sorter. mRNA expression of RANKL, osteoprotegerin, tumor necrosis factor (TNF) a, and Blimp 1 was analyzed by quantitative real time polymerase chain reaction. Levels of RANKL, CD80, CD86, and CXCR3 were analyzed using flow cytometry. Functional analysis of osteoclastogenesis was carried out in the co culture system using macrophage RAW264 reporter cells.ResultsRANKL expression was accentuated in CD80+CD86+ B cells, a highly activated B cell subset more abundantly observed in patients with rheumatoid arthritis. Upon activation via B cell receptor and CD40, switched memory B cells predominantly expressed RANKL, which was further augmented by interferon g (IFN g) but suppressed by interleukin 21.Strikingly, IFN g also enhanced TNF a expression, while it strongly suppressed osteoprotegerin expression in B cells. IFN g increased the generation of CXCR3+RANKL+ effector B cells, mimicking the synovial B cell phenotype in patients with rheumatoid arthritis. Finally, RANKL+ effector B cells in concert with TNF a facilitated osteoclast differentiation in vitro.ConclusionsOur current findings have shed light on the generation mechanism of pathogenic RANKL+ effector B cells that would be an ideal therapeutic target for rheumatoid arthritis in the future.
Arthritis Research Therapy