Expression of membrane-bound TRAIL in freshly isolated and IFNα-stimulated leukocytes. Neutrophils and PBMCs, purified from the same donor, were analyzed by flow cytometry immediately after isolation or after incubation for 24 hours in the absence or in the presence of 100 U/mL IFNα. Monocytes and lymphocytes were identified in the total PBMC population according to forward light scatter and side scatter parameters. Staining with anti-TRAIL mAb are indicated with normal and bold histograms for cells cultured in the absence or in the presence of IFNα, respectively. Dotted histograms represent staining with isotype control IgG1 mAbs. These profiles are representative of analyses performed in 5 healthy donors.