Effect of GM-CSF and LPS on the surface expression of HB-EGF molecule in PMN. PMN were cultured in the absence (A) or presence of 25 ng/mL GM-CSF (B) or 100 ng/mL LPS (C) for 21 hours. Only GM-CSF–treated PMN acquired membrane expression of the HB-EGF molecule (B). Membrane-bound HB-EGF expression was examined by indirect immunofluorescence analysis using the polyclonal H6 antibody (kindly provided by Dr S. Higashiyama), followed by a human-IgG preadsorbed biotinylated second antibody and by PE-conjugated streptavidin. Cells were also stained with irrelevant antibodies as controls. The expression patterns presented in this figure were reproduced in 5 independent experiments.