Increase in neutral sphingomyelinase activity in FMLP-activated and phagocytosing PMNs. Control, FMLP-activated, and phagocytosing FMLP-activated cells were fractionated as described in Experimental Procedures and in the legend to Fig 3. The bars show fold increase (+SEM) above control (set to 1) of total measured activity of neutral sphingomyelinase (SMase) and the various marker proteins after FMLP activation and phagocytosis. The total amount is calculated as the sum of measured amount in fractions 1 through 25, in nuclei and unbroken cells, and in exocytosed material (cell supernatant after activation). Data are the average of five experiments. *P < .05 compared with the control by paired t-test. None of the marker proteins differed significantly between control, FMLP, or phagocytosing cells.