Maintenance of Mcl-1 expression by GM-CSF and correlation with delayed apoptosis. In (A), Mcl-1 expression was determined by Western blotting and densitometric analysis as described in Materials and Methods after 2-, 4-, 6-, and 12-hour culture in medium alone (control, ○), with GM-CSF (▪), and with GM-CSF added to control incubations after 6-hour incubation of control suspensions (□). (B) shows the relationship between Mcl-1 expression (□) and nonapoptotic neutrophils (▧). Apoptosis was assessed by morphology as described in Materials and Methods, with Mcl-1 expression measured as in (A).