CD209 and rheumatoid arthritis: Flow cytometric analysis of HC, PsA and RA monocytes (representative histograms Figure 1B), show similar marked and statistically significant increases in the expression of the differentiation marker CD209 for all groups following 7 days stimulation with GM-CSF/IL-4 (p < 0.001) (Figure 1B), paralleled by a reduction in CD14 expression (Figure 1C).