ULBP1 and central nervous system cancer: First, we monitored by flow cytometry the cell surface expression of the NKG2D ligand MICA, MICB, ULBP1, ULBP2, ULBP3, ULBP4 and MHC class I on untreated and SR141716-treated U251 glioma cells at 24 h to exclude that the possibility of observed effects are linked to the stress of dying cells.