Immunofluorescence staining of FLT-4 and FLK-1 in TrHBMEC. TrHBMEC were cultured in chamber slides and fixed with 4% paraformaldehyde. After blocking, the cells were immunostained with antibodies to FLT-4 (A) or FLK-1 (B), followed by secondary antibodies conjugated with FITC. Normal rabbit IgG was used as a negative control (C). HUVEC were used as a positive control for FLK-1 expression (data not shown).