Lupus PBMCs fail to form mature EC monolayers. (A) Control PBMCs were plated into fibronectin-coated wells in complete EC media. On day 15, cells were stained with anti–VWF-FITC, UEA-1–Texas red, and Hoechst 33342 and analyzed by fluorescent microscopy. Images are from 1 representative healthy control and show single fluorophores and a merged image (bottom; × 20 objective magnification). (B) On day 15, wells were examined for EC monolayer development. Representative images of PBMC-derived cells from a healthy control and a lupus patient (× 5 objective magnification). See “In vitro differentiation into mature ECs” for more image acquisition information. (C) The y-axis represents the percentage of controls (13/14) or lupus patients (7/33) that formed an EC monolayer.