CD123 plasmacytoid dendritic cells from Sezary syndrome patients are decreased in numbers but express normal levels of TLR9. (A) PBMCs from SS patients with low (n = 5), medium (n = 4), and high (n = 4) peripheral blood tumor burdens and healthy volunteers (n = 6) were excluded of all lineage-positive cells (Lin 1-FITC cocktail), and lineage-negative cells were analyzed for the co-expression HLADR and CD123. Data represent means (± SD) of tested individuals and are presented as a percentage of all PBMCs gated on live cells. (B) PBMCs from SS patients and healthy volunteers were stained as described in panel A, but lineage-negative cells were analyzed for the co-expression of HLADR, CD123, and TLR9 or isotype control antibody. Control antibody stained 0.1% to 0.3% of PBMCs (data not shown). Data represent means (± SD) of tested individuals and are presented as a percentage of CD123 DCs expressing TLR9. ^*P < .05 compared with healthy volunteers. (C) PBMCs from a representative healthy volunteer (top row) and high tumor burden patient (bottom row) were stained as described in panels A and B. The left upper quadrant numbers of panels on the left represent the percentage of dendritic cells in the healthy volunteer (percentage of all PBMCs gated on forward and side light scatter) and the patient, whereas the right upper quadrant numbers represent the percentage of CD123 DCs stained with isotype control. The right upper quadrant numbers of the panels on the right represent percentage of CD123 DCs positive for TLR9 in the healthy volunteer (top row) and the patient (bottom row).