Lipopolysaccharide protects polymorphonuclear leukocytes from apoptosis via tyrosine phosphorylation-dependent signal transduction pathways

Background. The present study was undertaken to determine if tyrosine phosphorylation signal transduction pathways, which are known to be activated in polymorphonuclear leukocytes (PMN) by lipopolysaccharide (LPS), play a role in priming of PMN oxidative burst and protection of PMN from apoptosis by LPS, and to determine if an interface between these two signaling pathways exists. Methods. PMN were combined with or without 10-fold serial dilutions (0.1 ng-1 mu g/ml) of LPS and incubated at 37 degrees C/5% CO2. After 24 h PMN apoptosis was assessed using fluorescence microscopy and DNA agarose gel electrophoresis. Additional PMN were pretreated with the tyrosine kinase inhibitors genistein and herbamycin A before addition of LPS. Tyrosine phosphorylation was detected by immunoblotting. Oxidant production was quantitated by following the oxidation of a chromophore to its fluorescent product. Results. LPS delayed the onset of apoptosis and prolonged the survival of PMN in a dose-dependent fash ion. Both tyrosine kinase inhibitors blocked the protective effect of LPS on PMN apoptosis; however, only genistein blocked the priming effect of LPS on PMN oxidative burst. Conclusions. Tyrosine phosphorylation signal transduction pathways are central to protection of PMN from apoptosis by LPS. Although tyrosine phosphorylation pathways also play a role in priming of the oxidative burst in PMN, our data suggest that there is not an interface between these important signaling pathways. (C) 1998 Academic Press.