Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency that manifests as increased susceptibility to many pathogens. Although the spectrum of infections suffered by WAS patients is consistent with defects in neutrophil (PMN) function, the consequences of WAS protein (WASp) deficiency on this innate immune cell have been unclear. We report that deficiency of WASp in both human and murine PMNs resulted in profound defects in clustering of beta2 integrins, leading to defective adhesion and transendothelial migration under conditions of physiologic shear flow. Wild-type PMNs redistributed clustered beta2 integrins to the uropod of the cell during active migration, whereas WASp-deficient cells remain unpolarized. The WASp-deficient PMNs also showed reduced integrin-dependent activation of degranulation and respiratory burst. PMNs from a WAS patient manifested similar defects in integrin clustering and signaling. These results suggest that impaired beta2 integrin function in WASp-deficient PMNs may contribute substantially to the clinical immunodeficiency suffered by WAS patients.

Abstract-Intracellular calcium flux is an early step in the signaling cascade that bridges ligation of selectin and chemokine receptors to activation of adhesive and motile functions during recruitment on inflamed endothelium. Calcium flux was imaged in real time and provided a means of correlating signaling events in neutrophils rolling on E-selectin and stimulated by chemokine in a microfluidic chamber. Integrin dependent neutrophil arrest was triggered by E-selectin tethering and ligation of IL-8 seconds before a rapid rise in intracellular calcium, which was followed by the onset of pseudopod formation. Calcium flux on rolling neutrophils increased in a shear dependent manner, and served to link integrin adhesion and signaling of cytoskeletally driven cell polarization. Abolishing calcium influx through membrane expressed store operated calcium channels inhibited activation of high affinity b 2 integrin and subsequent cell arrest. We conclude that calcium influx at the plasma membrane integrates chemotactic and adhesive signals, and functions to synchronize signaling of neutrophil arrest and migration in a shear stress dependent manner.

Orai1 was reported to function as a calcium channel subunit that facilitates store operated calcium entry (SOCE) in T cells and is necessary for formation of the immune synapse. We reasoned that SOCE via Orai1 might regulate PMNs activation during recruitment to inflamed endothelium.

We describe the development, validation, and application of a novel PDMS-based microfluidic device for imaging leukocyte interaction with a biological substrate at defined shear force employing a parallel plate geometry that optimizes experimental throughput while decreasing reagent consumption. The device is vacuum bonded above a standard 6-well tissue culture plate that accommodates a monolayer of endothelial cells, thereby providing a channel to directly observe the kinetics of leukocyte adhesion under defined shear flow. Computational fluid dynamics (CFD) was applied to model the shear stress and the trajectory of leukocytes within the flow channels at a micron length scale. In order to test this model, neutrophil capture, rolling, and deceleration to arrest as a function of time and position was imaged in the transparent channels. Neutrophil recruitment to the substrate proved to be highly sensitive to disturbances in flow streamlines, which enhanced the rate of neutrophil-surface collisions at the entrance to the channels. Downstream from these disturbances, the relationship between receptor mediated deceleration of rolling neutrophils and dose response of stimulation by the chemokine IL-8 was found to provide a functional readout of integrin activation. This microfluidic technique allows detailed kinetic studies of cell adhesion and reveals neutrophil activation within seconds to chemotactic molecules at concentrations in the picoMolar range.

Abstract-High levels of triglyceride-rich lipoproteins (TGRLs) in blood are linked to development of atherosclerosis, yet the mechanisms by which these particles initiate inflammation of endothelium are unknown. TGRL isolated from human plasma during the postprandial state was examined for its capacity to bind to cultured human aortic endothelial cells (HAECs) and alter the acute inflammatory response to tumor necrosis factor-␣. HAECs were repetitively incubated with dietary levels of freshly isolated TGRL for 2 hours per day for 1 to 3 days to mimic postprandial lipidemia. TGRL induced membrane upregulation of the low-density lipoprotein family receptors LRP and LR11, which was inhibited by the low-density lipoprotein receptor-associated protein-1. TGRLs alone did not elicit inflammation in HAECs but enhanced the inflammatory response via a 10-fold increase in sensitivity to cytokine stimulation. This was reflected by increased mitogen-activated protein kinase activation, nuclear translocation of NF-B, amplified expression of endothelial selectin and VCAM-1, and a subsequent increase in monocyte-specific recruitment under shear flow as quantified in a microfabricated vascular mimetic device. (Circ Res. 2007;100:381-390.)

Polymorphonuclear leukocyte (PMN) recruitment to vascular endothelium during acute inflammation involves cooperation between selectins, G-proteins, and ␤ 2 -integrins. LFA-1 (CD11a/CD18) affinity correlates with specific adhesion functions because a shift from low to intermediate affinity supports rolling on ICAM-1, whereas high affinity is associated with shear-resistant leukocyte arrest. We imaged PMN adhesion on cytokine-inflamed endothelium in a parallel-plate flow chamber to define the dynamics of ␤ 2 -integrin function during recruitment and transmigration. After arrest on inflamed endothelium, high-affinity LFA-1 aligned along the uropod-pseudopod major axis, which was essential for efficient neutrophil polarization and subsequent transmigration. IntroductionNeutrophils are recruited at vascular sites of acute inflammation by the sequential binding of selectins, CXC chemokines, and ␤ 2 -integrins that function cooperatively to elicit rolling, arrest, and transmigration. From observations of neutrophil recruitment in the murine microcirculation and on endothelial monolayers grown in tissue culture, a number of rules of engagement have emerged. First, Mac-1 (␣ M ␤ 2 ) and LFA-1 (␣ L ␤ 2 ) are necessary and sufficient for neutrophil arrest and transmigration, with each subunit providing distinct adhesive contributions throughout the process from rolling to transmigration. 1-3 Second, polymorphonuclear leukocyte (PMN) rolling on a monolayer of cells coexpressing E-selectin and intercellular adhesion molecule-1 (ICAM-1) is sufficient to induce selectin ligand clustering (PSGL-1 and L-selectin) and to signal a shift in LFA-1 and Mac-1 from low to high affinity to bind ICAM-1. This process is synergistic with chemokine signaling on rolling PMN to amplify the efficiency of arrest. 4,5 LFA-1 appears to function early in this process in that it participates in tethering to ICAM-1 as it shifts from low to intermediate and high affinity. 6,7 How changes in conformation of the heterodimer result in changes in affinity to interact with ICAM-1 and mediate rolling, arrest, and outside-in signaling is only partially defined. 8 Structural studies of LFA-1 reveal that extension and activation of ICAM-1 binding involves an inserted or I-domain on the ␣-subunit and an I-like domain on the ␤-subunit that exerts a pull on the C-terminal ␣ 7 -helix of the ␣-subunit, leading to the open shape of the heterodimer and high-affinity ligand binding. 9,[10][11][12] This conformational shift to high affinity can be stabilized by binding of Mg 2ϩ or Mn 2ϩ or by inside-out signaling by chemokine receptors. 9,13,14 Once activated by a chemokine such as IL-8 or SDF-1, extension and opening of the LFA-1 heterodimer initiate rapid arrest on ICAM-1, as do activated I-domain mutants. 6,[15][16][17][18] Counteracting a shift to high affinity, small molecule allosteric anti-inflammatory inhibitors of LFA-1 function by effectively stabilizing the low-affinity state and antagonize binding to ICAM-1 and leukocyte adhesion. 19,20 XVA143 is one such ...

Objective-Atherosclerosis is a focal disease that develops at sites of low and oscillatory shear stress in arteries. This study aimed to understand how endothelial cells sense a gradient of fluid shear stress and transduce signals that regulate membrane expression of cell adhesion molecules and monocyte recruitment.Methods-Human aortic endothelial cells were stimulated with TNF-α and simultaneously exposed to a linear gradient of shear stress that increased from 0 to 16 dyne/cm 2 . Cell adhesion molecule expression and activation of NFκB were quantified by immunofluorescence microscopy with resolution at the level of a single endothelial cell. Monocyte recruitment was imaged using custom microfluidic flow chambers.Results-VCAM-1 and E-selectin upregulation was greatest between 2-4 dyne/cm 2 (6 and 4-fold, respectively) and above 8 dyne/cm 2 expression was suppressed below that of untreated endothelial cells. In contrast, ICAM-1 expression and NFκB nuclear translocation increased with shear stress up to a maximum at 9 dyne/cm 2 . Monocyte recruitment was most efficient in regions where E-selectin and VCAM-1 expression was greatest.Conclusions-We found that the endothelium can sense a change in shear stress on the order of 0.25 dyne/cm 2 over a length of ~10 cells, regulating the level of protein transcription, cellular adhesion molecule expression, and leukocyte recruitment during inflammation.

We present an innovative centrifugal microfluidic immunoassay platform (SpinDx) to address the urgent biodefense and public health need for ultrasensitive point-of-care/incident detection of botulinum toxin. The simple, sample-to-answer centrifugal microfluidic immunoassay approach is based on binding of toxins to antibody-laden capture particles followed by sedimentation of the particles through a density-media in a microfluidic disk and quantification by laser-induced fluorescence. A blind, head-to-head comparison study of SpinDx versus the gold-standard mouse bioassay demonstrates 100-fold improvement in sensitivity (limit of detection = 0.09 pg/mL), while achieving total sample-to-answer time of <30 min with 2-μL required volume of the unprocessed sample. We further demonstrate quantification of botulinum toxin in both exogeneous (human blood and serum spiked with toxins) and endogeneous (serum from mice intoxicated via oral, intranasal, and intravenous routes) samples. SpinDx can analyze, without any sample preparation, multiple sample types including whole blood, serum, and food. It is readily expandable to additional analytes as the assay reagents (i.e., the capture beads and detection antibodies) are disconnected from the disk architecture and the reader, facilitating rapid development of new assays. SpinDx can also serve as a general-purpose immunoassay platform applicable to diagnosis of other conditions and diseases.