DEMONSTRATION OF REVERSIBLE PRIMING OF HUMAN NEUTROPHILS USING PLATELET-ACTIVATING-FACTOR

Exposure of neutrophils to agents such as lipopolysaccharide, tumor ne crosis factor-alpha (TNF-alpha), and the granulocyte-macrophage colony -stimulating factor causes a major upregulation of subsequent agonist- induced NADPH oxidase activation. This priming effect is a prerequisit e for neutrophil-mediated tissue damage and has been widely considered to be an irreversible process. We have investigated the potential for neutrophils to recover from a priming stimulus by studying the effect s of platelet-activating factor (PAF). PAF did not stimulate respirato ry burst activity directly, but caused a rapid (maximal at 10 minutes) and concentration-dependent (EC (50) 50.2 nmol/L) increase in N-formy l-methionyl-leucyl-phenylalanine (fMLP)-stimulated superoxide anion re lease. At time-points >10 minutes, this priming effect spontaneously d eclined, with return to basal levels of fMLP-stimulated superoxide ani on generation by 120 minutes. An identical priming timecourse was obse rved with N-methyl carbamyl PAF, a nonmetabolizable analogue of PAF, i ndicating that the transient nature of PAF-induced priming was not sec ondary to PAF metabolism. Two structurally diverse PAF receptor antago nists (UK-74,505 and WEB 2086), added 10 minutes after PAF addition, i ncreased the rate of decay of the priming effect. In contrast, TNF-alp ha-induced priming, which was of a similar magnitude to that observed for PAF, was slower to evolve (maximal at 30 minutes) and remained con stant for at least 120 minutes. The reversible nature of PAF-induced p riming was confirmed by demonstrating that PAF-, but not TNF-alpha-, i nduced cell polarization (shape change) and CD11b-dependent neutrophil binding of albumin-coated latex beads was also transient, with return to basal, unstimulated levels by 120 minutes. Furthermore, cells that had spontaneously deprimed following PAF exposure retained their capa city to be fully reprimed by a subsequent addition of either PAF or TN F-alpha. These data imply that neutrophil priming is not an irreversib le event: the demonstration of a cycle of complete priming, depriming, and repriming offers the potential for functional recycling of neutro phils at sites of inflammation. (C) 1996 by The American Society of He matology.