Morphologic features of PMN cultured with GM-CSF in the presence or absence of DT. Only after GM-CSF treatment, PMN acquired sensitivity to DT, which induced typical apoptotic features. Cytospin preparations of PMN were stained using the May-Grünwald-Giemsa method after incubation in vitro for 21 hours in the presence or absence of 0.5 ng/mL GM-CSF with or without 10⁻⁸ mol/L DT. The experiment depicted is representative of 2.