Extracellular signal-regulated kinase and p38 have been shown to be cleaved in human neutrophils undergoing apoptosis induced by tumor necrosis factor-alpha and cycloheximide. However, the cleavage products of these molecules were undetected when apoptotic neutrophils were pretreated with phenylmethylsulfonyl fluoride OF disrupted by nitrogen cavitation before preparation of cell lysates. The electron Microscopy revealed that granules in apoptotic neutrophils were significantly swollen than those in control cells. These findings Suggest that granule membrane may become destabilized during neutrophil apoptosis, leading to rapid proteolysis of these molecules by granule-derived serine proteases during preparation of cell lysates with the conventional lysis buffer. (C) 2009 Elsevier Inc. All rights reserved