VWF and glioblastoma: Similarly, double-label immunofluorescence analysis for integrin α3 and the EC marker, von Willebrand factor (vwf), on tissue obtained from the Cleveland Clinic Brain Tumor Bank and the Department of Pathology showed significantly higher mean fluorescence intensity of the integrin α3 subunit in TECs in eight GBM as compared to NECs in nine normal brains (Fig. 2g and Supplementary Fig. 6).