Lipopolysaccharide-induced priming of the human neutrophil is not associated with a change in phosphotyrosine phosphatase activity

The activation of the neutrophil respiratory burst is a two-step process in volving an initial 'priming' phase followed by a 'triggering' event. The bi ochemical mechanisms which underlie these events are yet to be fully elucid ated, but the evidence suggests a crucial role for stimulus-induced tyrosin e phosphorylation, The enhanced tyrosine phosphorylation observed upon trig gering primed cells may reflect an increase in tyrosine kinase activity or a reduction in the levels of the opposing phosphotyrosine phosphatases (PTP ases). We have investigated the latter by examining the possibility that li popolysaccharide (LPS)-induced priming of the neutrophil respiratory burst involves the suppression of cellular PTPase activity. Purified human neutro phils were incubated for 60 min with and without LPS, Priming of the respir atory burst was confirmed by fMet-Leu-Phe-induced cytochrome c reduction. T he level of PTPase activity was assessed by dephosphorylation of [P-32]RR-s rc peptide as substrate. Pretreatment of human neutrophils with 200 ng/ml L PS induced a 2.9 +/- 0.3 (mean +/- SEM, n = 3, P = 0.022) fold increase in the fMet-Leu-Phe-triggered respiratory burst. In the same cells, LPS did no t induce a significant change in the total cellular PTPase activity (1.02 /- 0.02-fold, mean +/- SEM, n = 3, P = 0.63). Similarly, stimulation of neu trophils with Met-Leu-Phe or phorbol myristate acetate did not significantl y affect the cellular PTPase activity (P = 0.94 and 0.68, respectively). Ou r results suggest that suppression of PTPase activity is not the mechanism underlying the priming and or triggering of the neutrophil respiratory burs t. (C) 1999 Elsevier Science Ltd. All rights reserved.