IL-1α and LPS downregulate c-kit receptor expression on the surface of HUVEC and ECV 304 (A through C) but not on CD34⁺ cells (D and E). Cells were stained using direct immunofluorescence with a PE-conjugated anti-CD 117 MoAb (anti–c-kit) (CD34⁺ cells) or indirect immunofluorescence using a PE-labeled secondary antibody (HUVEC, ECV 304). Background fluorescence (control) was measured using an irrelevant isotype FITC-conjugated antibody.