Background
Rheumatoid arthritis (RA) is an autoimmune disease that is characterized by chronic inflammation of the joints leading to destruction of cartilage and bone. RA is characterized by synovial lining hyperplasia and chronic infiltration by T and B cells, monocyte/macrophages, dendritic cells (DC) and other cells. DC are the only antigen-presenting cells that can prime naïve Th cells and initiate immune responses. In peripheral blood two major DC subsets can be found: BDCA1+CD11c+CD123low (myeloid), with the ability to produce IL-12; and BDCA4+CD11c-CD123high (plasmacytoid), which produce large amounts of type I interferons (IFN-α/β).