APRIL is produced mainly by neutrophils infiltrating DLBCL lesions. Stalk-1 staining (green) was combined to (A) anti-CD15 (1 of 50), (B) antielastase (1 μg/mL), (C) anti-L1 protein (10 μg/mL), and (D) antivimentin (5 μg/mL) stainings (all in red). Single stainings and corresponding merge pictures shown are representative of 2 or more patients with DLBCL. (E) Morphology of Stalk-1–stained cells. (F-H) Intensity of Stalk-1 staining is shown for a cell with a morphology of (F) a neutrophil, (G) a histiocyte, and (H) a mesenchymal cell from the same lesion. The pictures were taken with the same exposure time. (I) The picture shows endothelial cells lining tumor-draining vessels (arrow) and blood neutrophils stained with Stalk-1.(J) Stalk-1 staining (green) was combined to anti-CD20 staining (red, 5 μg/mL) and analyzed by confocal microscopy. Single stainings and corresponding merge picture are representative of 6 patients with DLBCL.