Release of the soluble form of HB-EGF by PMN and PBMC. GM-CSF treatment induces release of the HB-EGF molecule into the culture medium (P < .05). (A) PMN and PBMC were cultured alone or in the presence of either 0.5 ng/mL GM-CSF or 100 ng/mL LPS. Cell-free SN were collected after 21 hours, and the levels of soluble HB-EGF protein were measured by a specific ELISA. The levels of soluble HB-EGF spontaneously released by the U937 cell line were also determined for comparison. (B) In selected experiments, PMN-derived SN were concentrated approximately 80-fold before ELISA detection. Values represent means (±SD) of duplicate determinations calculated from 3 independent experiments.