Journal
JOURNAL OF CELL BIOLOGY
Volume 191, Issue 6, Pages 1205-1218Publisher
ROCKEFELLER UNIV PRESS
DOI: 10.1083/jcb.201007056
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Funding
- Canadian Institutes of Health Research (CIHR) [7075]
- CIHR [PRG-80174]
- NIH [P50 GM068762, U01 GM067230]
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Binding of ligands by immunoreceptors is thought to be a passive, stochastic process. Contrary to this notion, we found that binding of IgG-opsonized particles by Fc gamma receptors was inhibited in macrophages, dendritic and microglial cells by agents that interfere with actin assembly or disassembly. Changes in the lateral mobility of the receptors-assessed by single-particle tracking-or in the microelasticity of the membrane-determined by atomic-force microscopy-could not account for the effects of actin disruption on particle binding. Instead, we found that the macrophages contact their targets by actively extending actin-rich structures. Formation of these protrusions is driven by Rac and requires phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate. Capture of C3bi-opsonized as well as unopsonized targets by macrophages was also dependent on actin. Thus, phagocytes continuously probe their environment for foreign particles in a manner akin to the constitutive sampling of the fluid milieu by dendritic cells. Active probing by phagocytes is most important when confronted by scarcely opsonized and/or highly mobile targets.
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