Protective effect of NWS from G-CSF–treated donors over aGVHD is abolished in the absence of granulocytes. (C57BL/6 × BALB/c) F1 mice were lethally irradiated and received T cell–depleted BM alone (BMTD only) or together with nylon wool spleen (NWS) cells, NWS cells from G-CSF–treated donor (G-NWS), or NWS cells from G-CSF–treated donor mice after granulocyte depletion (G-NWSD). (A) Percentages of surviving animals. Log rank: P = .05 between G-NWS and G-NWSD and between BMTD and G-NWS. (B) NWS from C57BL/6 control, G-NWS, or G-NWSD were stained with anti-Gr1 FITC, as indicated in “Materials and methods.” Inset: SSC × FSC dot plots of the same histogram samples (note the high SSC cells in G-NWS that are not present in G-NWSD). (C) Histopathology of the small intestine. Moderate inflammatory infiltrate in the lamina propria (asterisk and inset) associated with extensive epithelial cell sloughing (arrows) of NWS (left panel); villous atrophy and mild inflammatory infiltrate in lamina propria of G-NWS (middle panel) and marked mucosal atrophy, luminal cell debris, and accumulation of inflammatory cells in lamina propria (asterisk) of G-NWSD (right panel). Inset: Apoptotic crypt epithelial cell (broad arrow). Original magnification, 100 × (left panel); 200 × (middle and right panels); 1000 × (inset). Data are from 1 of 2 representative experiments (with 4 to 5 animals/group) for panels A and C and 1 of 5 representative experiments for panel B.