Cellular memory: Neutrophil orientation reverses during temporally decreasing chemoattractant concentrations

Abstract

Cell directional orientation or shape polarization is the first cellular step in neutrophil locomotion. To better understand how chemoattractants interact with cells, we studied neutrophil polarization (or shape changes) during exposure to a temporally decreasing chemoattractant signal of N-formyl-methionyl-leucyl-phenylalanine (FMLP) in the absence of a spatial concentration gradient. To accomplish this objective, we used a manifold of differing FMLP concentrations attached to a stopped-f low microscope chamber. Spatial gradients of a f luorescent chemotactic peptide could not be detected in the chamber by using microf luorometry. When FMLP was injected at continually increasing concentrations at 10-s intervals, the shape and relative direction of the neutrophil persisted. However, when temporally decreasing FMLP concentrations were injected, Ϸ80% of the cells changed their direction with 44% of the total cells swinging about to 180°؎ 15°. Most of these directional changes involved dissolution of both the lamellipodium and uropod and reformation of these structures 180°from their original positions. This research suggests that neutrophils reverse their morphological polarity when exposed to temporally decreasing ligand concentrations by ''remembering'' their ligand exposure history and relative direction.Neutrophils participate in inflammatory responses, such as host resistance to infectious disease, and in deleterious host inflammatory reactions, including arthritis, septic shock, and ischemia͞reperfusion injury of tissues during heart attack, stroke, and transplantation. To reach inflammatory sites, neutrophils must first recognize adhesion molecules of endothelial cells lining the circulatory system. Subsequently, neutrophils efficiently cross tissue planes, basement membranes, and interstitial tissues to reach inflammatory foci. Spontaneous neutrophil locomotion involves a series of coordinated cellular processes including oscillatory changes in integrin adhesiveness, signaling, pericellular proteolysis, oxidant production, and actin assembly (1-9). Directed locomotion or chemotaxis additionally involves the ligation of specific chemotaxin receptors, such as the formyl peptide receptors (10). For example, ligation of the formyl peptide receptor leads to the activation of cellular G protein-coupled signaling pathways (11). However, how the activation of G protein pathways promotes chemotaxis and how cells process chemoattractant information during locomotion are uncertain (12, 13).To begin to dissect the problem of neutrophil chemoattractant signal processing, in contrast to simple transmembrane chemical reactions, we have studied cell polarization, the first cellular step in neutrophil locomotion. During polarization for locomotion, neutrophils generate well defined morphological features, including a lamellipodium at the leading edge and a uropod at the trailing end. To focus on the temporal component of signal processing, we used a stopped-flow microscopy chamber to remove the spatial component or...

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Selective Localization of Recognition Complexes for Leukotriene B4 and Formyl-Met-Leu-Phe within Lipid Raft Microdomains of Human Polymorphonuclear Neutrophils

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Modeling emergent tissue organization involving high-speed migrating cells in a flow equilibrium

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