CERAMIDE SELECTIVELY INHIBITS EARLY EVENTS IN THE RESPONSE OF HUMAN NEUTROPHILS TO TUMOR-NECROSIS-FACTOR

Cell spreading and the respiratory burst of neutrophils responding to soluble, physiological agents and adherent to model biological surface s are typically delayed in onset by 15 min or more, The lag period may be a physiologically important feature of the action of such agents o n neutrophils in that it may allow for migration before secretion, How ever, the mechanism that interposes such a long delay between stimulus and response is unknown. Tumor necrosis factor alpha (TNF-alpha) medi ates some of its actions by triggering sphingomyelinase to generate ce ramide, In adherent human neutrophils, however, exogenous ceramide did not mimic TNF-alpha's ability to stimulate cell spreading, paxillin t yrosine phosphorylation, or the respiratory burst. On the contrary, ce ramide suppressed each such response, Ceramide did so by extending the lag period in the cells' response to TNF-alpha. Ceramide extended the lag period whether it was added exogenously or generated endogenously by sphingomyelinase, and the effect was reversible, Remarkably, howev er, ceramide inhibited cell spreading or the respiratory burst only if added together with TNF-alpha or within the next few minutes, Neutrop hils ignored ceramide if it was added later, even if the TNF-alpha-tri ggered respiratory burst had not yet commenced, These features suggest that an early, brief elevation of ceramide in response to TNF-alpha c ould mediate the lag period, By temporarily inhibiting tyrosine phosph orylation, cell spreading, acid the respiratory burst, ceramide or a f unctionally similar mediator could serve as a phase coordinator of the neutrophil's response to soluble agonists.