SiMA: A simplified migration assay for analyzing neutrophil migration

In vitro neutrophil migration is associated with inhaled corticosteroid treatment and serum cytokines in pediatric asthma

Background: Different asthma phenotypes are driven by molecular endotypes. A Th1-high phenotype is linked to severe, therapy-refractory asthma, subclinical infections and neutrophil inflammation. Previously, we found neutrophil granulocytes (NGs) from asthmatics exhibit decreased chemotaxis towards leukotriene B4 (LTB₄), a chemoattractant involved in inflammation response. We hypothesized that this pattern is driven by asthma in general and aggravated in a Th1-high phenotype.

Methods: NGs from asthmatic nd healthy children were stimulated with 10 nM LTB₄/100 nM N-formylmethionine-leucyl-phenylalanine and neutrophil migration was documented following our prior SiMA (simplified migration assay) workflow, capturing morphologic and dynamic parameters from single-cell tracking in the images. Demographic, clinical and serum cytokine data were determined in the ALLIANCE cohort.

Results: A reduced chemotactic response towards LTB₄ was confirmed in asthmatic donors regardless of inhaled corticosteroid (ICS) treatment. By contrast, only NGs from ICS-treated asthmatic children migrate similarly to controls with the exception of Th1-high donors, whose NGs presented a reduced and less directed migration towards the chemokines. ICS-treated and Th1-high asthmatic donors present an altered surface receptor profile, which partly correlates with migration.

Conclusions: Neutrophil migration in vitro may be affected by ICS-therapy or a Th1-high phenotype. This may be explained by alteration of receptor expression and could be used as a tool to monitor asthma treatment.

Method for simultaneous tracking of thousands of unlabeled cells within a transparent 3D matrix

Three-dimensional tracking of cells is one of the most powerful methods to investigate multicellular phenomena, such as ontogenesis, tumor formation or wound healing. However, 3D tracking in a biological environment usually requires fluorescent labeling of the cells and elaborate equipment, such as automated light sheet or confocal microscopy. Here we present a simple method for 3D tracking large numbers of unlabeled cells in a collagen matrix. Using a small lensless imaging setup, consisting of an LED and a photo sensor only, we were able to simultaneously track ~3000 human neutrophil granulocytes in a collagen droplet within an unusually large field of view (>50 mm²) at a time resolution of 4 seconds and a spatial resolution of ~1.5 μm in xy- and ~30 μm in z-direction. The setup, which is small enough to fit into any conventional incubator, was used to investigate chemotaxis towards interleukin-8 (IL-8 or CXCL8) and N-formylmethionyl-leucyl-phenylalanine (fMLP). The influence of varying stiffness and pore size of the embedding collagen matrix could also be quantified. Furthermore, we demonstrate our setup to be capable of telling apart healthy neutrophils from those where a condition of inflammation was (I) induced by exposure to lipopolysaccharide (LPS) and (II) caused by a pre-existing asthma condition. Over the course of our experiments we have tracked more than 420.000 cells. The large cell numbers increase statistical relevance to not only quantify cellular behavior in research, but to make it suitable for future diagnostic applications, too.

Neutrophils-From Bone Marrow to First-Line Defense of the Innate Immune System

Neutrophils (polymorphonuclear cells; PMNs) form a first line of defense against pathogens and are therefore an important component of the innate immune response. As a result of poorly controlled activation, however, PMNs can also mediate tissue damage in numerous diseases, often by increasing tissue inflammation and injury. According to current knowledge, PMNs are not only part of the pathogenesis of infectious and autoimmune diseases but also of conditions with disturbed tissue homeostasis such as trauma and shock. Scientific advances in the past two decades have changed the role of neutrophils from that of solely immune defense cells to cells that are responsible for the general integrity of the body, even in the absence of pathogens. To better understand PMN function in the human organism, our review outlines the role of PMNs within the innate immune system. This review provides an overview of the migration of PMNs from the vascular compartment to the target tissue as well as their chemotactic processes and illuminates crucial neutrophil immune properties at the site of the lesion. The review is focused on the formation of chemotactic gradients in interaction with the extracellular matrix (ECM) and the influence of the ECM on PMN function. In addition, our review summarizes current knowledge about the phenomenon of bidirectional and reverse PMN migration, neutrophil microtubules, and the microtubule organizing center in PMN migration. As a conclusive feature, we review and discuss new findings about neutrophil behavior in cancer environment and tumor tissue.

Ex vivo observation of granulocyte activity during thrombus formation

Background

The process of thrombus formation is thought to involve interactions between platelets and leukocytes. Leukocyte incorporation into growing thrombi has been well established in vivo, and a number of properties of platelet-leukocyte interactions critical for thrombus formation have been characterized in vitro in thromboinflammatory settings and have clinical relevance. Leukocyte activity can be impaired in distinct hereditary and acquired disorders of immunological nature, among which is Wiskott-Aldrich Syndrome (WAS). However, a more quantitative characterization of leukocyte behavior in thromboinflammatory conditions has been hampered by lack of approaches for its study ex vivo. Here, we aimed to develop an ex vivo model of thromboinflammation, and compared granulocyte behavior of WAS patients and healthy donors.

Results

Thrombus formation in anticoagulated whole blood from healthy volunteers and patients was visualized by fluorescent microscopy in parallel-plate flow chambers with fibrillar collagen type I coverslips. Moving granulocytes were observed in hirudinated or sodium citrate-recalcified blood under low wall shear rate conditions (100 s⁻¹). These cells crawled around thrombi in a step-wise manner with an average velocity of 90–120 nm/s. Pre-incubation of blood with granulocyte priming agents lead to a significant decrease in mean-velocity of the cells and increase in the number of adherent cells. The leukocytes from patients with WAS demonstrated a 1.5-fold lower mean velocity, in line with their impaired actin polymerization. It is noteworthy that in an experimental setting where patients’ platelets were replaced with healthy donor’s platelets the granulocytes’ crawling velocity did not change, thus proving that WASP (WAS protein) deficiency causes disruption of granulocytes’ behavior. Thereby, the observed features of granulocytes crawling are consistent with the neutrophil chemotaxis phenomenon. As most of the crawling granulocytes carried procoagulant platelets teared from thrombi, we propose that the role of granulocytes in thrombus formation is that of platelet scavengers.

Conclusions

We have developed an ex vivo experimental model applicable for observation of granulocyte activity in thrombus formation. Using the proposed setting, we observed a reduction of motility of granulocytes of patients with WAS. We suggest that our ex vivo approach should be useful both for basic and for clinical research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01238-x.

Gα13 Mediates Transendothelial Migration of Neutrophils by Promoting Integrin-Dependent Motility without Affecting Directionality

Neutrophil migration requires β₂ integrins and chemoattractant receptor signaling for motility and directionality. G protein subunit Gα₁₃ can facilitate cell migration by mediating RhoA activation induced by G protein-coupled receptors. However, the possible role of Gα₁₃-integrin interaction in migration is unclear. In this study, we show that Gα₁₃ ^-/- neutrophils are deficient in transendothelial migration and migration on β₂ integrin ligand ICAM-1. However, unlike G protein-coupled receptors and integrin inside-out signaling pathways, Gα₁₃ is important in migration velocity and neutrophil spreading but not in directionality nor cell adhesion. Importantly, neutrophil recruitment in vivo was also inhibited in Gα₁₃ ^-/- mice, suggesting the importance of Gα₁₃ in transendothelial migration of neutrophils in vitro and in vivo. Furthermore, a synthetic peptide (MB2mP6) derived from the Gα₁₃ binding site of β₂ inhibited Gα₁₃-β₂ interaction and Gα₁₃-mediated transient RhoA inhibition in neutrophils, suggesting that this peptide inhibited integrin outside-in signaling. MB2mP6 inhibited migration of control neutrophils through endothelial cell monolayers or ICAM-1-coated filters, but was without further effect on Gα₁₃ ^-/- neutrophils. It also inhibited integrin-dependent neutrophil migration velocity without affecting directionality. In vivo, MB2mP6 markedly inhibited neutrophil infiltration into the cardiac tissues induced by ischemia/reperfusion injury. Thus, Gα₁₃-dependent outside-in signaling enables integrin-dependent neutrophil motility without affecting directionality and may be a new therapeutic target for inhibiting neutrophil trafficking but not adhesion.

The influence of extracellular tissue on neutrophil function and its possible linkage to inflammatory diseases

BACKGROUND

Migration, production of reactive oxygen species (ROS), release of myeloperoxidase (MPO), and NETosis are functional immunological reactions of elementary importance for polymorphonuclear neutrophils (PMN). Unregulated inflammatory response of PMN within tissues plays a key role in the pathophysiology of several diseases. However, little is known about the behavior of PMN after migration through blood vessel walls. Therefore, we investigated the influence of the extracellular matrix (ECM) on PMN function.

MATERIALS AND METHODS

We established an in vitro chemotaxis model of type I and III collagen, fibrin, and herbal agarose tissues using µ-slide chemotaxis devices and N-formylmethionine-leucyl-phenylalanine (fMLP). PMN within the matrices were assessed with a fluorescent time-lapse microscope for live-cell imaging.

RESULTS

PMN function was obviously influenced by the ECM. Type III collagen had an inhibitory effect on PMN migration regarding track length, direction, and targeting. Type III collagen also had an accelerating effect on neutrophil ROS production. Agarose had an inhibitory effect on MPO release and fibrin a retarding effect on NETosis.

CONCLUSION

Because of the high abundance of type III collagen in lung and skin matrices, the interaction of PMN with the respective matrix could be an important mechanism in the pathophysiology of acute respiratory distress syndrome and pyoderma gangrenosum.

Microfluidic devices for neutrophil chemotaxis studies

Neutrophil chemotaxis plays a vital role in human immune system. Compared with traditional cell migration assays, the emergence of microfluidics provides a new research platform of cell chemotaxis study due to the advantages of visualization, precise control of chemical gradient, and small consumption of reagents. A series of microfluidic devices have been fabricated to study the behavior of neutrophils exposed on controlled, stable, and complex profiles of chemical concentration gradients. In addition, microfluidic technology offers a promising way to integrate the other functions, such as cell culture, separation and analysis into a single chip. Therefore, an overview of recent developments in microfluidic-based neutrophil chemotaxis studies is presented. Meanwhile, the strength and drawbacks of these devices are compared.

Impact of hydroxyethyl starch and modified fluid gelatin on granulocyte phenotype and function

BACKGROUND

Patients with neutropenia or granulocyte dysfunction may require granulocyte transfusions for adequate immune restoration. High-molecular-weight hydroxyethyl starch (HES) is the most commonly used sedimentation agent to enhance granulocyte collection efficiency. However, authorities recently restricted the use of HES due to its unfavorable risk-benefit profile. As modified fluid gelatin (MFG) is already used as an alternative sedimentation agent, we tested the hypothesis that MFG is not inferior to HES in terms of the functionality and viability of granulocytes.

STUDY DESIGN AND METHODS

Granulocytes from ten healthy donors were isolated, aliquoted and incubated in parallel for 2 hours with either 0% (control), 7.5%, 15%, or 30% MFG (Gelafundin) or HES (Hespan), respectively, and granulocyte migration, chemotaxis, reactive oxygen species (ROS) production, neutrophil extracellular trap formation (NETosis), antigen expression, and viability were subsequently investigated in vitro.

RESULTS

Relative to the controls, all three concentrations of HES compared to only 15% and 30% MFG lowered migration distances, and the 15% and 30% concentrations of both sedimentation agents reduced track straightness. HES resulted in lower CD11b expression and higher CD62L expression compared to MFG and the controls, whereas the differences for CD66b did not reach statistical significance. No significant differences in the timing of ROS production or NETosis, or in neutrophil viability or respiratory burst were observed.

CONCLUSION

These results indicate that MFG is not inferior to HES in terms of granulocyte function in vitro when used at equal concentrations, and that potential impairment of granulocyte function can occur with HES.

Tumstatin fragment selectively inhibits neutrophil infiltration in experimental asthma exacerbation

BACKGROUND

Asthma is a chronic inflammatory disease with structural changes present. Burgess and colleagues recently found tumstatin markedly reduced in adult asthmatic lung tissue compared with nonasthmatics. ECM fragments such as tumstatin are named matrikines and act independently of the parent molecule. The role of Col IV matrikines in neutrophil inflammation (eg. exacerbation in asthma) has not been investigated to date. Severe adult asthma phenotypes are dominated by neutrophilic inflammation and show a high frequency of severe exacerbations.

OBJECTIVE

This study sought to investigate the role of a novel active region within tumstatin (CP17) and its implication in neutrophil inflammatory responses related to asthma exacerbation.

METHODS

For reactive oxygen production, isolated neutrophils were preincubated with peptides or vehicle for 1 hour and stimulated (PMA). Luminescence signal was recorded (integration over 10 seconds) for 1.5 hours. Neutrophil migration was performed according to the SiMA protocol. Mice were sensitized to OVA/Alumn by intraperitoneal (i.p.) injections. Mice were then treated with CP17, vehicle (PBS) or scrambled peptide (SP17) after OVA exposure (days 27 and 28, polyI:C stimulation). All animals were killed on day 29 with lung function measurement, histology and lavage.

RESULTS

CP17 decreased total ROS production rate to 52.44% (0.5 μmol/L, P < 0.05 vs SP17), reduced the in vitro directionality (vs SP17, P = 1 × 10^-6 ) and migration speed (5 μmol/L, P = 1 × 10^-3 ). In vivo application of CP17 decreased neutrophil inflammation ~1.8-fold (P < 0.001 vs SP17) and reduced numbers of mucus-producing cells (-29%, P < 0.05).

CONCLUSION

CP17 reduced the ROS production rate, migrational speed and selectively inhibited neutrophil accumulation in the lung interstitium and lumen.

CLINICAL RELEVANCE

CP17 may serve as a potential precursor for drug development to combat overwhelming neutrophil inflammation.

Mechanochemical modeling of neutrophil migration based on four signaling layers, integrin dynamics, and substrate stiffness

Directional neutrophil migration during human immune responses is a highly coordinated process regulated by both biochemical and biomechanical environments. In this paper, we developed an integrative mathematical model of neutrophil migration using a lattice Boltzmann-particle method built in-house to solve the moving boundary problem with spatiotemporal regulation of biochemical components. The mechanical features of the cell cortex are modeled by a series of spring-connected nodes representing discrete cell-substrate adhesive sites. The intracellular signaling cascades responsible for cytoskeletal remodeling [e.g., small GTPases, phosphoinositide-3-kinase (PI3K), and phosphatase and tensin homolog] are built based on our previous four-layered signaling model centered on the bidirectional molecular transport mechanism and implemented as reaction-diffusion equations. Focal adhesion dynamics are determined by force-dependent integrin-ligand binding kinetics and integrin recycling and are thus integrated with cell motion. Using numerical simulations, the model reproduces the major features of cell migration in response to uniform and gradient biochemical stimuli based on the quantitative spatiotemporal regulation of signaling molecules, which agree with experimental observations. The existence of multiple types of integrins with different binding kinetics could act as an adaptation mechanism for substrate stiffness. Moreover, cells can perform reversal, U-turn, or lock-on behaviors depending on the steepness of the reversal biochemical signals received. Finally, this model is also applied to predict the responses of mutants in which PTEN is overexpressed or disrupted.

Hypothetical protein Cpn0423 triggers NOD2 activation and contributes to Chlamydia pneumoniae-mediated inflammation

BACKGROUND

Chlamydia pneumoniae (C. pneumoniae) is pathogenic to humans, by causing pulmonary inflammation or bronchitis in both adolescents and young adults. However, the molecular signals linking C. pneumoniae components to inflammation remain elusive. This study was to investigate the effect of Chlamydia-specific Cpn0423 of C. pneumoniae on C. pneumoniae-mediated inflammation.

RESULTS

Cpn0423 was detected outside of C. pneumoniae inclusions, which induced production of several cytokines including macrophage inflammatory protein-2 (MIP-2) and interleukins (ILs). Production of the Cpn0423-induced cytokines was markedly reduced in cells pretreated with NOD2-siRNA, but not with negative control oligonucleotides. Mice treated with Cpn0423 through intranasal administration exhibited pulmonary inflammation as evidenced by infiltration of inflammatory cells, increased inflammatory scores in the lung histology, recruitment of neutrophils and increased cytokines levels in the BALF.

CONCLUSION

Cpn0423 could be sensed by NOD2, which was identified as an essential element in a pathway contributing to the development of C. pneumoniae -mediated inflammation.

Tumstatin regulates the angiogenic and inflammatory potential of airway smooth muscle extracellular matrix

The extracellular matrix (ECM) creates the microenvironment of the tissue; an altered ECM in the asthmatic airway may be central in airway inflammation and remodelling. Tumstatin is a collagen IV‐derived matrikine reduced in the asthmatic airway wall that reverses airway inflammation and remodelling in small and large animal models of asthma. This study hypothesized that the mechanisms underlying the broad asthma‐resolving effects of tumstatin were due to autocrine remodelling of the ECM. Neutrophils and endothelial cells were seeded on decellularized ECM of non‐asthmatic (NA) or asthmatic (A) airway smooth muscle (ASM) cells previously exposed to tumstatin in the presence or absence of a broad matrix metalloproteinase inhibitor, Marimastat. Gene expression in NA and A ASM induced by tumstatin was assessed using RT‐PCR arrays. The presence of tumstatin during ECM deposition affected neutrophil and endothelial cell properties on both NA and A ASM‐derived matrices and this was only partly due to MMP activity. Gene expression patterns in response to tumstatin in NA and A ASM cells were different. Tumstatin may foster an anti‐inflammatory and anti‐angiogenic microenvironment by modifying ASM‐derived ECM. Further work is required to examine whether restoring tumstatin levels in the asthmatic airway represents a potential novel therapeutic approach.