Figure 11.

In vitro model suggests that expression of myeloid markers in tumor lymphatic vessels might result from fusion. Red fluorescent protein (RFP)–tagged rat lymphatic endothelial cells (RLECs) were cocultured for 4 to 6 days with the green fluorescent protein (GFP)–tagged macrophage cell line RAW264.7 in the presence of 3 nmol/L lipopolysaccharide or vehicle. Cells were monitored daily using a fluorescent microscope. A: Contact between the two cell types was observed on days 2 to 3 when most cells contained a single nucleus. B: Fusion between the two cell types was observed on days 4 to 5, as indicated by colocalization of RFP and GFP and the presence of two nuclei in the cell with overlapping colors (white asterisk). C: On days 4 to 6, multinucleated RFP⁺/GFP⁺ cells containing up to nine nuclei in a single cell were observed, as highlighted by the white boxed area. The latter image was acquired at a higher magnification (inset) to highlight the numerous nuclei present in the single cell. White arrowheads point to double-positive cells for GFP and RFP indicating fusion. Scale bar = 20 μm (A–C). Original magnification: ×600 (A–C); ×1200 (C, inset).