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

Abstract

The activation of the neutrophil respiratory burst is a two-step process involving an initial `priming' phase followed by a `triggering' event. The biochemical mechanisms which underlie these events are yet to be fully elucidated, but the evidence suggests a crucial role for stimulus-induced tyrosine phosphorylation. The enhanced tyrosine phosphorylation observed upon triggering primed cells may reflect an increase in tyrosine kinase activity or a reduction in the levels of the opposing phosphotyrosine phosphatases (PTPases). We have investigated the latter by examining the possibility that lipopolysaccharide (LPS)-induced priming of the neutrophil respiratory burst involves the suppression of cellular PTPase activity. Purified human neutrophils were incubated for 60 min with and without LPS. Priming of the respiratory burst was confirmed by fMet–Leu–Phe-induced cytochrome c reduction. The level of PTPase activity was assessed by dephosphorylation of [ 32P]RR- src peptide as substrate. Pretreatment of human neutrophils with 200 ng/ml LPS 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 not 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 neutrophils with fMet–Leu–Phe or phorbol myristate acetate did not significantly affect the cellular PTPase activity ( P=0.94 and 0.68, respectively). Our results suggest that suppression of PTPase activity is not the mechanism underlying the priming and/or triggering of the neutrophil respiratory burst.