TSP-1 enhances apoptotic monocyte interaction with iDCs, and inhibits DC maturation. (A) TSP-1 enhances apoptotic monocyte interaction with iDCs. Apoptotic monocytes were stained with DiI and offered to iDCs, at a 4:1 ratio. The iDCs acquired apoptotic cell-derived DiI. A control group of iDCs was not exposed to apoptotic monocytes. Addition of 2 μg/mL exogenous TSP-1 significantly increased (60%, P < .001), with median fluorescence from 601 (in the absence of TSP-1) to 960 (in the presence of TSP-1). Apo monocytes indicates apoptotic monocytes. Results are representative of 5 experiments. (B) iDC maturation is inhibited by TSP-1 in the presence of apoptotic monocytes. Expression of CD86 and HLA-DR on iDCs following exposure to 5 ng/mL LPS. In the presence of apoptotic monocytes, marked down-regulation of CD86 and DR was documented (P < .001). Addition of 2 μg/mL TSP-1 even further inhibited DR and CD86 expression (P < .001). Anti-DR-FITC (top panel) and anti-CD86-FITC (bottom panel) are presented. Numbers indicating the median fluorescence are presented in each histogram. Isotype controls are shown as gray-filled curves.