Ratios of DC subsets in tissue compartments. Myeloid dendritic cell/plasmacytoid dendritic cell (mDC:pDC) ratios in synovial fluid (SF) are significantly increased when compared with matched peripheral blood (PB). (a) The mDC:pDC ratio in PB from rheumatoid arthritis (RA) subjects (n = 12), psoriatic arthritis (PsA) subjects (n = 13) and osteoarthritis (OA) subjects (n = 11) was not significantly altered compared with healthy control subjects (n = 12); median and interquartile range are shown. (b) The mDC:pDC ratio in SF from RA subjects (n = 6) and PsA subjects (n = 6) was significantly increased compared with matched PB samples. Squares indicate individual matched samples. The ratio was calculated from total number of cells per millilitre. *P < 0.05, **P < 0.01.