The N-terminal (heparin-binding) domain and CD36 mediate engulfment capacity for apoptotic monocytes, and multiple domains mediate the immunosuppressive effect. iDCs were exposed to several blocking antibodies directed against various potential TSP-1 receptors, washed, and then offered DiI-stained apoptotic monocytes in the presence of 2 μg/mL TSP-1. (A) TSP-1-dependent apoptotic monocyte engulfment is mediated mainly through the HBD. Striking (90%) inhibition of apoptotic monocyte uptake is seen upon inhibition of binding through the HBD (P < .001). Significant uptake inhibition is seen upon inhibition of CD36 (64%, P < .001), whereas slight uptake inhibition is observed upon neutralizing CD51 (24%, P < .05). No significant engulfment inhibition is seen when CD47 and β1-integrin domains (CD29) are inhibited. Inhibition is presented as a percentage of TSP-1-dependent engulfment. Data are mean ± SEM of 3 experiments. (B-C) TSP-1-induced maturation inhibition involves multiple domains. Expression of DR (B) and CD86 (C) was indicative of the level of DC maturation. iDCs were treated with inhibiting antibodies as described under “Inhibition assays,” and were then exposed to TSP-1 with or without the addition of apoptotic monocytes. LPS (5 ng/mL) was added 5 hours later, and expression of DR and CD86 was examined 20 hours later. As shown, the main effect was achieved by blocking HBD (P < .001), but other binding sites, such as CD36, CD29 (β1 integrins), CD51, and CD47, also had important immunosuppressive effects (P < .001 for each site). The relative inhibition effects on maturation are expressed as the relative changes in DR and CD86 median fluorescence of DCs, compared with DCs treated with isotype control and exposed to LPS. Data are mean ± SEM of 4 experiments.