Background
Dendritic cells (DC) comprise a heterogeneous network of professional antigen-presenting cells, directly linking innate and adaptive immunity. While implicated in the pathogenesis of different chronic inflammatory arthritides, the analysis of DC subsets has been hampered by a lack of specific DC markers and reliable quantitation. Previously, we have described the significant reduction of circulating peripheral blood (PB) myeloid DC (mDC) in rheumatoid arthritis (RA) patients and the significant reduction of circulating PB plasmacytoid DC (pDC) in both RA and psoriatic arthritis patients. Furthermore, we have shown that both of these DC subsets are present in synovial fluid (SF) from RA and psoriatic arthritis patients, although mDC significantly exceed pDC.