Dataset Information

Immobilized IL-8 Triggers Phagocytosis and Dynamic Changes in Membrane Microtopology in Human Neutrophils.

ABSTRACT: The interaction of leukocytes with surface bound ligands can be limited by the location of the molecules relative to the surface topology of the cell. In this report, we examine the dynamic response of neutrophils to IL-8-fractalkine chimera immobilized on bead surfaces, taking into account changes in receptor occupancy resulting from changes in surface topography. As a readout for receptor signaling, we observe the dynamics of calcium release in neutrophils following contact with the IL-8 coated surface. After a delay that depended on the initial area of contact and the surface density of IL-8, the cell began to phagocytose the IL-8 coated bead. This appeared to be a pre-requisite for release of calcium, which typically followed shortly after the initiation of phagocytosis. In separate experiments, effective kinetic coefficients for the formation of bonds between immobilized IL-8 and receptors on the cell surface were determined. Using these coefficients, we were able to estimate the number of bound receptors in the nascent contact zone. Kinetic modeling of the signaling response predicted that cell spreading and a concomitant increase in the density of occupied receptors would be required for the experimentally observed calcium dynamics. Postulating that there is an increase in receptor occupancy resulting from smoothing of the cell surface as it is stretched over the bead enabled us to obtain model predictions consistent with experimental observations. This study reveals the likely importance of membrane microtopology as a rate-limiting property and potential means of regulation of cell responses stimulated by two-dimensional surface interactions.

SUBMITTER: Beste MT

PROVIDER: S-EPMC4500759 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature

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Immobilized IL-8 Triggers Phagocytosis and Dynamic Changes in Membrane Microtopology in Human Neutrophils.

Beste Michael T MT Lomakina Elena B EB Hammer Daniel A DA Waugh Richard E RE

Annals of biomedical engineering 20150113 9

The interaction of leukocytes with surface bound ligands can be limited by the location of the molecules relative to the surface topology of the cell. In this report, we examine the dynamic response of neutrophils to IL-8-fractalkine chimera immobilized on bead surfaces, taking into account changes in receptor occupancy resulting from changes in surface topography. As a readout for receptor signaling, we observe the dynamics of calcium release in neutrophils following contact with the IL-8 coate ...[more]

PMID: 25582838

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Project description:Targeted drug carriers are attractive for the delivery of therapeutics directly to the site of a disease, reducing systemic side effects and enhancing the efficacy of therapeutic molecules. However, the use of particulate carriers for drug delivery comes with its own set of challenges and barriers. Among these, a great deal of research effort has focused on protecting carriers from clearance by phagocytes via altering carrier surface chemistry, mostly with the use of polyethylene glycol (PEG) chain coatings. However, few papers have explored the effects of PEGylation on uptake by freshly-obtained primary human phagocytes in physiological conditions. In this work, we investigate the effect of PEGylation on particle uptake by primary human neutrophils in vitro and compare these effects to several cell lines and other model phagocytic cells systems. We find that human neutrophils in whole blood preferentially phagocytose PEGylated particles (e.g., ∼40% particle positive neutrophils for PEGylated versus ∼20% for carboxylated polystyrene microspheres) and that this effect is linked to factors present in human plasma. Model phagocytes internalized PEGylated particles less efficiently or equivalently to carboxylated particles in culture medium but preferentially phagocytosed PEGylated particles in the human plasma (e.g., ∼86% versus ∼63% PEGylated versus carboxylated particle positive cells, respectively). These findings have significant implications for the efficacy of PEGylation in designing long-circulating drug carriers, as well as the need for thorough characterization of drug carrier platforms in a wide array of in vitro and in vivo assays.Statement of significanceThe work in this manuscript is highly significant to the field of drug delivery, as it explores in-depth the effects of polyethylene glycol (PEG) coatings, which are frequently used to prevent phagocytic clearance of particulate drug carriers, on the phagocytosis of such carriers by neutrophils, the most abundant leukocyte in blood circulation. Surprisingly, we find that PEGylation enhances uptake by primary human neutrophils, specifically in the presence of human plasma. This result suggests that PEGylation may not confer the benefits in humans once thought, and may help to explain why PEG has not become the "magic bullet" it was once thought to be in the field of particulate drug delivery.

Dataset Information

Immobilized IL-8 Triggers Phagocytosis and Dynamic Changes in Membrane Microtopology in Human Neutrophils.

Publications

Immobilized IL-8 Triggers Phagocytosis and Dynamic Changes in Membrane Microtopology in Human Neutrophils.

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