D6 expression is dynamic and regulated by lymphangiogenic and inflammatory cytokines. (Ai) Lymphatic endothelia in human psoriatic skin stained for D6 (green) and the lymphatic marker podoplanin (red). 4,6 diamidino-2-phenylindole (DAPI; blue) stains the nuclei. Some vessels stain strongly for D6 (top right inset), whereas others are negative for D6 expression (bottom left inset). (Aii) In vitro cultured lymphatic endothelial cells display D6 immunoreactivity (green) in punctate intracellular vesicles. DAPI (blue) stains the nuclei. (B) D6 is expressed by cultured HDLECs and is downregulated with repeat passage during continuous culture, as determined by QPCR. D6 transcript levels in HDLECs were assessed by QPCR and shown to be regulated by (C) lymphangiogenic factors, (D) anti-inflammatory cytokines, (E) type I interferons, and (F) pro-inflammatory cytokines. Cytokines were used at the following concentrations: transforming growth factor (TGF)-β and IL-1α (10 ng/mL); TNF-α (20 ng/mL); CCL2 (30 ng/mL); IL-3 and IL-10 (50 ng/mL); TNF-β and vascular endothelial growth factors (VEGF; 100 ng/mL); vitamin D3 (10 μM); and IFN-α/β (100 μ/mL). *P < .05.