Abstract
The actin-related protein (ARP) 2/3 complex, essential for organizing and nucleating branched actin filaments, is required for several cellular immune processes, including cell migration and granule exocytosis. Recently, genetic defects in ARPC1B, a subunit of this complex, were reported. Mutations in ARPC1B result in defective ARP2/3-dependent actin filament branching, leading to a combined immunodeficiency with severe inflammation. In vitro, neutrophils of these patients showed defects in actin polymerization and chemotaxis, whereas adhesion was not altered under static conditions. Here we show that under physiological flow conditions human ARPC1B-deficient neutrophils were able to transmigrate through TNF-α-pre-activated endothelial cells with a decreased efficiency and, once transmigrated, showed definite impairment in subendothelial crawling. Furthermore, severe locomotion and migration defects were observed in a 3D collagen matrix and a perfusable vessel-on-a-chip model. These data illustrate that neutrophils employ ARP2/3-independent steps of adhesion strengthening for transmigration but rely on ARP2/3-dependent modes of migration in a more complex multidimensional environment.
Highlights
Neutrophils are the most abundant type of leukocytes in the human circulation and important effector cells in the innate immune system
We investigated the capacity of neutrophils to transmigrate through an endothelial monolayer under physiological flow conditions
HUVECs were grown on fibronectin, and stimulated with tumor necrosis factor-alpha (TNF-a) which leads to the upregulation of cell adhesion molecules such as ICAM-1 and VCAM-1, as well as the production of important chemoattractants for neutrophils like platelet-activating factor and interleukin-8 [9, 10]
Summary
Neutrophils are the most abundant type of leukocytes in the human circulation and important effector cells in the innate immune system They are the first cells recruited to sites of infection or inflammation, where they extravasate through the blood vessel into the tissue. Once neutrophils cross the endothelial cell layer they encounter a second barrier, the vascular basement membrane (BM) This BM provides structural support for endothelial cells and is composed of a network of multiple extracellular matrix (ECM) proteins, including laminins and collagen type IV [2]. After crossing these layers, neutrophils continue to migrate and enter the tissue to reach and fight infection
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