Figure 2. SCARF1 is a non-redundant efferocytosis receptor on BDCA1⁺ DCs.

(A) SCARF1 is internalized after interacting with apoptotic cells. PBMCs (1x10⁶ cells/mL) from healthy controls (n=5) were stimulated with apoptotic cells (2x10⁶ cells/mL) for 1 hour. After 1 hour, media was removed, and new media was added. Cells were incubated for 3 hours, and PBMCs were surface stained for flow cytometry. Data represent the mean (±SEM) of three independent experiments with 1–2 independent donors. Percent reduction is shown on the graph. ***P<0.001. (B) SCARF1 is a phagocytic receptor for apoptotic cells in conventional DCs. MUTZ-3 DC line confocal images of SCARF1 (green), DNA (blue, DAPI), and apoptotic cells (red) 2 hours post-stimulation. Representative images from 2 independent experiments with 3 replicates. Scale=40x (left and middle), 20x (right). Arrows show the colocalization of apoptotic cells and SCARF1. (C-D) Blocking SCARF1 reduces apoptotic cell uptake. PBMCs (1x10⁶/mL) were incubated with anti-SCARF1 for 30 minutes, then stimulated with pHrodo red-labeled apoptotic cells (2x10⁶/mL). Cells were incubated for 3 hours and then stained and analyzed by flow cytometry against CD45⁺CD11c⁺BDCA1⁺ (BDCA1⁺ DCs) or CD45⁺CD11c^intCD11b⁺CD14⁺ (CD14⁺ monocytes). (C) Representative histogram of 3 independent experiments. (D) MFI quantification of internalization by pHrodo. BDCA1⁺ DCs (red), CD14⁺ monocytes (blue). Data represents the mean (±SEM) of 3 independent experiments, P< *(0.05) ***(0.0001) ns (not significant) by two-way ANOVA.