Microfluidic platform for the quantitative analysis of leukocyte migration signatures

Impaired LTB4-induced neutrophil chemotactic directionality in myelodysplastic neoplasms patients

OBJECTIVES

Myelodysplastic neoplasm (MDS) patients are at a high risk of infections, contributing significantly to morbidity and mortality. While neutrophil dysfunction is considered a primary factor, specific functional defects remain elusive.

METHODS

We conducted a comprehensive study involving 90 participants, including controls and de novo MDS patients. We utilized the TAXIScan-FL system to evaluate neutrophil chemotaxis towards leukotriene B4 (LTB4). The global reactive oxygen species (ROS) production by neutrophils were measured by chemiluminescence assay, neutrophil alkaline phosphatase (NAP) was evaluated by enzymatic staining.

RESULTS

MDS patients, irrespective of absolute neutrophil count (ANC) levels, exhibited elevated empirical antimicrobial therapy (EAT) rate compared to controls. Neutrophil migration towards LTB4 was notably impaired, demonstrating reduced velocity and directionality. Interestingly, MDS patients with high ANC still displayed poor directionality and slower migration. MDS patients also had compromised ROS and NAP activity. A noteworthy correlation was observed between EAT rate and chemotactic directionality parameters.

CONCLUSION

MDS patients face a heightened risk of infection, potentially attributed to impaired neutrophil chemotactic speed and directionality, alongside compromised ROS and NAP activity. Notably, chemotactic directionality emerged as a pivotal factor correlated with antimicrobial therapy. These insights hold significant clinical implications for managing infections in MDS patients, underscoring the importance of targeting specific neutrophil defects for more effective therapeutic strategies.

Confinement by Liquid-Liquid Interface Replicates In Vivo Neutrophil Deformations and Elicits Bleb-Based Migration

Leukocytes forge paths through interstitial spaces by exerting forces to overcome confining mechanical pressures provided by surrounding cells. While such mechanical cues regulate leukocyte motility, engineering an in vitro system that models the deformable cellular environment encountered in vivo has been challenging. Here, microchannels are constructed with a liquid-liquid interface that exerts confining pressures similar to cells in tissues, and thus, is deformable by cell-generated forces. Consequently, the balance between migratory cell-generated and interfacial pressures determines the degree of confinement. Pioneer cells that first contact the interfacial barrier require greater deformation forces to forge a path for migration, and as a result migrate slower than trailing cells. Critically, resistive pressures are tunable by controlling the curvature of the liquid interface, which regulates motility. By granting cells autonomy in determining their confinement, and tuning environmental resistance, interfacial deformations match those of surrounding cells in vivo during interstitial neutrophil migration in a larval zebrafish model. It is discovered that neutrophils employ a bleb-based mechanism of force generation to deform a soft barrier exerting cell-scale confining pressures. In all, this work introduces a tunable in vitro material interface that replicates confining pressures applied by soft tissue environments.

Development of small-molecule fluorescent probes targeting neutrophils via N-formyl peptide receptors

N-Formyl peptide receptors (FPRs) are membrane receptors that are abundantly expressed in innate immune cells, including neutrophils and platelets, demonstrating potential new targets for immune system regulation and the treatment of inflammatory conditions. We report here the development and bio-physical validation of new FPR imaging agents as effective tools to track FPR distribution, localisation and functions, ultimately helping to establish FPR exact roles and functions in pathological and physiological conditions. The new series of probes feature a small molecule-based FPR address system conjugated to suitable fluorophores, resulting in highly specific FPR agents, including a partial agonist endowed with high affinity (i.e. low/sub-nanomolar potency) on FPR-transfected cells and human neutrophils. Preliminary imaging studies via multiphoton microscopy demonstrate that the probes enable the visualisation of FPRs in live cells, thus representing valid bio-imaging tools for the analysis of FPR-mediated signalling, such as the activation of neutrophils in inflammatory events.

Immunomodulation by allograft endothelial cells

It is increasingly appreciated that the expression of immunoregulatory molecules within tumors have potential to shape a microenvironment that promotes local immunoevasion and immunoregulation. However, little is known about tissue-intrinsic immunomodulatory mechanisms following transplantation. We propose that differences in the phenotype of microvascular endothelial cells impact the alloantigenicity of the graft and its potential to promote immunoregulation following transplantation. We focus this review on the concept that graft-dependent immunoregulation may evolve post-transplantation, and that it is dependent on the phenotype of select subsets of intragraft endothelial cells. We also discuss evidence that long-term graft survival is critically dependent on adaptive interactions among immune cells and endothelial cells within the transplanted tissue microenvironment.

Extracellular vesicles from diverse fungal pathogens induce species-specific and endocytosis-dependent immunomodulation

Microbial pathogens generate extracellular vesicles (EVs) for intercellular communication and quorum sensing. Microbial EVs also induce inflammatory pathways within host innate immune cells. We previously demonstrated that EVs secreted by Candida albicans trigger type I interferon signaling in host cells specifically via the cGAS-STING innate immune signaling pathway. Here, we show that despite sharing similar properties of morphology and internal DNA content, the interactions between EVs and the innate immune system differ according to the parental fungal species. EVs secreted by C. albicans, Saccharomyces cerevisiae, Cryptococcus neoformans, and Aspergillus fumigatus are endocytosed at different rates by murine macrophages triggering varied cytokine responses, innate immune signaling, and subsequent immune cell recruitment. Notably, cell wall constituents that decorate C. neoformans and A. fumigatus EVs inhibit efficient internalization by macrophages and dampen innate immune activation. Our data uncover the transcriptional and functional consequences of the internalization of diverse fungal EVs by immune cells and reveal novel insights into the early innate immune response to distinct clinically significant fungal pathogens.

A microphysiological assay for studying T-cell chemotaxis, trafficking and tumor killing

Tumors in patients non-responsive to immunotherapy harbor a series of barriers that impede the efficacy of effector T-cells. Consequently, therapeutically modulating the chemotaxis machinery to enable effector T cell infiltration and function in the tumor could result in more successful therapeutic outcomes. Complexin-vitromodels allow re-creation ofin-vivotumor complexities in anin-vitrosetting, allowing improved translatability to patient biology at the laboratory scale. We identified a gap in available industrial scale microphysiological (MPS) assays for faster validation of targets and strategies that enable T-cell chemotaxis and effector function within tumor microenvironments. Using a commercially available, 96-chip 2-lane microfluidic assay system, we present a novel, scalable, complexin vitroMPS assay to study 3D T-cell chemotaxis and function within native, extracellular matrix (ECM)-rich multicellular tumor environments. Activated or naïve CD3+ T-cells stained with far-red nuclear stain responded to the chemokine gradients generated within the matrigel-collagen ECM by migrating into the microfluidic channel (∼5 mm horizontal window), in a concentration- and cell type-dependent manner. Furthermore, we observed and tracked chemotaxis and cancer cell killing function of antigen-specific CD4.CD8. chimeric antigen receptor (CAR)-T cells that responded to CXCR3 agonist gradient built through the expansive 5 mm of cancer cell colony containing stroma. The 2-lane assay system yielded useful information regarding donor and dose-dependent differences in CAR-T cell chemotaxis and tumor killing. The scalable assay system allows a granular window into immune cell migration and function in tissue spaces beyond endothelium, addressing a missing gap in studying tissue-specific immune cell chemotaxis and function to bring forward advancements in cancer immunotherapy.

Confinement by liquid-liquid interface replicates in vivo neutrophil deformations and elicits bleb based migration

Leukocytes navigate through interstitial spaces resulting in deformation of both the motile leukocytes and surrounding cells. Creating an in vitro system that models the deformable cellular environment encountered in vivo has been challenging. Here, we engineer microchannels with a liquid-liquid interface that exerts confining pressures (200-3000 Pa) similar to cells in tissues, and, thus, is deformable by cell generated forces. Consequently, the balance between migratory cell-generated and interfacial pressures determines the degree of confinement. Pioneer cells that first contact the interfacial barrier require greater deformation forces to forge a path for migration, and as a result migrate slower than trailing cells. Critically, resistive pressures are tunable by controlling the curvature of the liquid interface, which regulates motility. By granting cells autonomy in determining their confinement, and tuning environmental resistance, interfacial deformations are made to match those of surrounding cells in vivo during interstitial neutrophil migration in a larval zebrafish model. We discover that, in this context, neutrophils employ a bleb-based mechanism of force generation to deform a barrier exerting cell-scale confining pressures.

An agent-based method to estimate 3D cell migration trajectories from 2D measurements: Quantifying and comparing T vs CAR-T 3D cell migration

BACKGROUND AND OBJECTIVE

Immune cell migration is one of the key features that enable immune cells to find invading pathogens, control tissue damage, and eliminate primary developing tumors. Chimeric antigen receptor (CAR) T-cell therapy is a novel strategy in the battle against various cancers. It has been successful in treating hematological tumors, yet it still faces many challenges in the case of solid tumors. In this work, we evaluate the three-dimensional (3D) migration capacity of T and CAR-T cells within dense collagen-based hydrogels. Quantifying three-dimensional (3D) cell migration requires microscopy techniques that may not be readily accessible. Thus, we introduce a straightforward mathematical model designed to infer 3D trajectories of cells from two-dimensional (2D) cell trajectories.

METHODS

We develop a 3D agent-based model (ABM) that simulates the temporal changes in the direction of migration with an inverse transform sampling method. Then, we propose an optimization procedure to accurately orient cell migration over time to reproduce cell migration from 2D experimental cell trajectories. With this model, we simulate cell migration assays of T and CAR-T cells in microfluidic devices conducted under hydrogels with different concentrations of type I collagen and validate our 3D cell migration predictions with light-sheet microscopy.

RESULTS

Our findings indicate that CAR-T cell migration is more sensitive to collagen concentration increases than T cells, resulting in a more pronounced reduction in their invasiveness. Moreover, our computational model reveals significant differences in 3D movement patterns between T and CAR-T cells. T cells exhibit migratory behavior in 3D whereas that CAR-T cells predominantly move within the XY plane, with limited movement in the Z direction. However, upon the introduction of a CXCL12 chemical gradient, CAR-T cells present migration patterns that closely resemble those of T cells.

CONCLUSIONS

This framework demonstrates that 2D projections of 3D trajectories may not accurately represent real migration patterns. Moreover, it offers a tool to estimate 3D migration patterns from 2D experimental data, which can be easily obtained with automatic quantification algorithms. This approach helps reduce the need for sophisticated and expensive microscopy equipment required in laboratories, as well as the computational burden involved in producing and analyzing 3D experimental data.

Profiling migration of human monocytes in response to chemotactic and barotactic guidance cues

Monocytes are critical to innate immunity, participating in chemotaxis during tissue injury, infection, and inflammatory conditions. However, the migration dynamics of human monocytes under different guidance cues are not well characterized. Here, we developed a microfluidic device to profile the migration characteristics of human monocytes under chemotactic and barotactic guidance cues while also assessing the effects of age and cytokine stimulation. Human monocytes preferentially migrated toward the CCL2 gradient through confined microchannels, regardless of donor age and migration pathway. Stimulation with interferon (IFN)-γ, but not granulocyte-macrophage colony-stimulating factor (GM-CSF), disrupted monocyte navigation through complex paths and decreased monocyte CCL2 chemotaxis, velocity, and CCR2 expression. Additionally, monocytes exhibited a bias toward low-hydraulic-resistance pathways in asymmetric environments, which remained consistent across donor ages, cytokine stimulation, and chemoattractants. This microfluidic system provides insights into the unique migratory behaviors of human monocytes and is a valuable tool for studying peripheral immune cell migration in health and disease.

CTC-Race: Single-Cell Motility Assay of Circulating Tumor Cells from Metastatic Lung Cancer Patients

Distinctive subpopulations of circulating tumor cells (CTCs) with increased motility are considered to possess enhanced tumor-initiating potential and contribute to metastasis. Single-cell analysis of the migratory CTCs may increase our understanding of the metastatic process, yet most studies are limited by technical challenges associated with the isolation and characterization of these cells due to their extreme scarcity and heterogeneity. We report a microfluidic method based on CTCs' chemotactic motility, termed as CTC-Race assay, that can analyze migrating CTCs from metastatic non-small-cell lung cancer (NSCLC) patients with advanced tumor stages and enable concurrent biophysical and biochemical characterization of them with single-cell resolution. Analyses of motile CTCs in the CTC-Race assay, in synergy with other single cell characterization techniques, could provide insights into cancer metastasis.

Immunity-on-a-Chip: Integration of Immune Components into the Scheme of Organ-on-a-Chip Systems

Studying the immune system in vitro aims to understand how, when, and where the immune cells migrate/differentiate and respond to the various triggering events and the decision points along the immune response journey. It becomes evident that organ-on-a-chip (OOC) technology has a superior capability to recapitulate the cell-cell and tissue-tissue interaction in the body, with a great potential to provide tools for tracking the paracrine signaling with high spatial-temporal precision and implementing in situ real-time, non-destructive detection assays, therefore, enabling extraction of mechanistic information rather than phenotypic information. However, despite the rapid development in this technology, integration of the immune system into OOC devices stays among the least navigated tasks, with immune cells still the major missing components in the developed models. This is mainly due to the complexity of the immune system and the reductionist methodology of the OOC modules. Dedicated research in this field is demanded to establish the understanding of mechanism-based disease endotypes rather than phenotypes. Herein, we systemically present a synthesis of the state-of-the-art of immune-cantered OOC technology. We comprehensively outlined what is achieved and identified the technology gaps emphasizing the missing components required to establish immune-competent OOCs and bridge these gaps.

A Comparative Inflammation-on-a-Chip with a Complete 3D Interface: Pharmacological Applications in COPD-Induced Neutrophil Migration

Chronic obstructive pulmonary disease (COPD) is a slow-progressing inflammatory lung disease that is associated with high mortality and disability. There is a lack of appropriate preclinical models of COPD, which hampers drug discovery efforts. Herein, a comparative inflammation-on-a-chip (IoC) is developed with a complete 3D interface without the formation of any micropillar and phaseguide structures that replicated chemoattractant-induced neutrophil transendothelial migration (NTEM), a key feature of COPD. The IoC model is used to evaluate the pharmacological effects of CXCR2 inhibitors (MK-7123, AZD5069, and SB225002) on the migration of neutrophil-like cells in the presence of plasma samples from patients with COPD. This is the first study to evaluate inhibitors of CXCR2-dependent NTEM in a comparative IoC model that mimics the physiological 3D microenvironment, consisting of an endothelial barrier, extracellular compartment, and inflammatory conditions. This IoC model will be useful to investigate COPD severity using patient samples, and will aid basic and translational research involving NTEM.

iCLOTS: open-source, artificial intelligence-enabled software for analyses of blood cells in microfluidic and microscopy-based assays

While microscopy-based cellular assays, including microfluidics, have significantly advanced over the last several decades, there has not been concurrent development of widely-accessible techniques to analyze time-dependent microscopy data incorporating phenomena such as fluid flow and dynamic cell adhesion. As such, experimentalists typically rely on error-prone and time-consuming manual analysis, resulting in lost resolution and missed opportunities for innovative metrics. We present a user-adaptable toolkit packaged into the open-source, standalone Interactive Cellular assay Labeled Observation and Tracking Software (iCLOTS). We benchmark cell adhesion, single-cell tracking, velocity profile, and multiscale microfluidic-centric applications with blood samples, the prototypical biofluid specimen. Moreover, machine learning algorithms characterize previously imperceptible data groupings from numerical outputs. Free to download/use, iCLOTS addresses a need for a field stymied by a lack of analytical tools for innovative, physiologically-relevant assays of any design, democratizing use of well-validated algorithms for all end-user biomedical researchers who would benefit from advanced computational methods.

Analytical device miniaturization for the detection of circulating biomarkers

Diverse (sub)cellular materials are secreted by cells into the systemic circulation at different stages of disease progression. These circulating biomarkers include whole cells, such as circulating tumour cells, subcellular extracellular vesicles and cell-free factors such as DNA, RNA and proteins. The biophysical and biomolecular state of circulating biomarkers carry a rich repertoire of molecular information that can be captured in the form of liquid biopsies for disease detection and monitoring. In this Review, we discuss miniaturized platforms that allow the minimally invasive and rapid detection and analysis of circulating biomarkers, accounting for their differences in size, concentration and molecular composition. We examine differently scaled materials and devices that can enrich, measure and analyse specific circulating biomarkers, outlining their distinct detection challenges. Finally, we highlight emerging opportunities in biomarker and device integration and provide key future milestones for their clinical translation.

A Bidirectional Single-Cell Migration and Retrieval Chip for Quantitative Study of Dendritic Cell Migration

Dendritic cell (DC) migration is a fundamental step during execution of its adaptive immunity functions. Studying DC migration characteristics is critical for development of DC-dependent allergy treatments, vaccines, and cancer immunotherapies. Here, a microfluidics-based single-cell migration platform is described that enables high-throughput and precise bidirectional cell migration assays. It also allows selective retrieval of cell subpopulations that have different migratory potentials. Using this microfluidic platform, DC migration is investigated in response to different chemoattractants and inhibitors, quantitatively describe DC migration patterns and retrieve DC subpopulations of different migratory potentials for differential gene expression analysis. This platform opens an avenue for precise characterization of cell migration and potential discovery of therapeutic modulators.

A meta-analysis indicates that the regulation of cell motility is a non-intrinsic function of chemoattractant receptors that is governed independently of directional sensing

Chemoattraction, defined as the migration of a cell toward a source of a chemical gradient, is controlled by chemoattractant receptors. Chemoattraction involves two basic activities, namely, directional sensing, a molecular mechanism that detects the direction of a source of chemoattractant, and actin-based motility, which allows the migration of a cell towards it. Current models assume first, that chemoattractant receptors govern both directional sensing and motility (most commonly inducing an increase in the migratory speed of the cells, i.e. chemokinesis), and, second, that the signaling pathways controlling both activities are intertwined. We performed a meta-analysis to reassess these two points. From this study emerge two main findings. First, although many chemoattractant receptors govern directional sensing, there are also receptors that do not regulate cell motility, suggesting that is the ability to control directional sensing, not motility, that best defines a chemoattractant receptor. Second, multiple experimental data suggest that receptor-controlled directional sensing and motility can be controlled independently. We hypothesize that this independence may be based on the existence of separated signalling modules that selectively govern directional sensing and motility in chemotactic cells. Together, the information gathered can be useful to update current models representing the signalling from chemoattractant receptors. The new models may facilitate the development of strategies for a more effective pharmacological modulation of chemoattractant receptor-controlled chemoattraction in health and disease.

Generation of Dynamic Concentration Profile Using A Microfluidic Device Integrating Pneumatic Microvalves

Generating and maintaining the concentration dilutions of diffusible molecules in microchannels is critical for high-throughput chemical and biological analysis. Conventional serial network microfluidic technologies can generate high orders of arbitrary concentrations by a predefined microchannel network. However, a previous design requires a large occupancy area and is unable to dynamically generate different profiles in the same chip, limiting its applications. This study developed a microfluidic device enabling dynamic variations of both the concentration in the same channel and the concentration distribution in multiple channels by adjusting the flow resistance using programmable pneumatic microvalves. The key component (the pneumatic microvalve) allowed dynamic adjustment of the concentration profile but occupied a tiny space. Additionally, a Matlab program was developed to calculate the flow rates and flow resistance of various sections of the device, which provided theoretical guidance for dimension design. In silico investigations were conducted to evaluate the microvalve deformation with widths from 100 to 300 µm and membrane thicknesses of 20 and 30 µm under the activation pressures between 0 and 2000 mbar. The flow resistance of the deformed valve was studied both numerically and experimentally and an empirical model for valve flow resistance with the form of Rh=aebP was proposed. Afterward, the fluid flow in the valve region was characterized using Micro PIV to further demonstrate the adjustment mechanism of the flow resistance. Then, the herringbone structures were employed for fast mixing to allow both quick variation of concentration and minor space usage of the channel network. Finally, an empirical formula-supported computational program was developed to provide the activation pressures required for the specific concentration profile. Both linear (Ck = -0.2k + 1) and nonlinear (Ck = (110)k) concentration distribution in four channels were varied using the same device by adjusting microvalves. The device demonstrated the capability to control the concentration profile dynamically in a small space, offering superior application potentials in analytical chemistry, drug screening, and cell biology research.

Antibody-functionalized aluminum oxide-coated particles targeting neutrophil receptors in a multifrequency microfluidic impedance cytometer

Personalized diagnostics of infectious diseases require monitoring disease progression due to their ever-changing physiological conditions and the multi-faceted organ system mechanisms involved in disease pathogenesis. In such instances, the recommended clinical strategies involve multiplexing data collection from critical biomarkers related to a patient's conditions along with longitudinal frequent patient monitoring. Numerous detection technologies exist both in research and commercial settings to monitor these conditions, however, they fail to provide biomarker multiplexing ability with design and data processing simplicity. For a recently conceived multiplexing biomarker modality, this work demonstrates the use of electrically sensitive microparticles targeting and identifying membrane receptors on leukocytes using a single detection source, with a high potential for multiplexing greater than any existing impedance-based single-detection scheme. Here, polystyrene microparticles are coated with varying thicknesses of metal oxides, which generate quantifiable impedance shifts when exposed to multifrequency electric fields depending on the metal oxide thickness. Using multifrequency impedance cytometry, these particles can be measured and differentiated rapidly across one coplanar electrode scheme. After surface-functionalizing particles with antibodies targeting CD11b and CD66b receptors, the particles are combined with isolated neutrophils to measure receptor expression. A combination of data analysis techniques including multivariate analysis, supervised machine learning, and unsupervised machine learning was able to accurately differentiate samples with up to 91% accuracy. This proof-of-concept study demonstrates the potential for these oxide-coated particles for enumerating specific leukocytes enabling multiplexing. Further, additional coating thicknesses or different metal oxide materials can enable a compendium of multiplexing targeting resource to be used to develop a high-multiplexing sensor for targeting membrane receptor expression.

Microfluidic Lab-on-a-Chip for Studies of Cell Migration under Spatial Confinement

Understanding cell migration is a key step in unraveling many physiological phenomena and predicting several pathologies, such as cancer metastasis. In particular, confinement has been proven to be a key factor in the cellular migration strategy choice. As our insight in the field improves, new tools are needed in order to empower biologists’ analysis capabilities. In this framework, microfluidic devices have been used to engineer the mechanical and spatial stimuli and to investigate cellular migration response in a more controlled way. In this work, we will review the existing technologies employed in the realization of microfluidic cellular migration assays, namely the soft lithography of PDMS and hydrogels and femtosecond laser micromachining. We will give an overview of the state of the art of these devices, focusing on the different geometrical configurations that have been exploited to study specific aspects of cellular migration. Our scope is to highlight the advantages and possibilities given by each approach and to envisage the future developments in in vitro migration studies under spatial confinement in microfluidic devices.

Tissue Models for Neisseria gonorrhoeae Research—From 2D to 3D

Neisseria gonorrhoeae is a human-specific pathogen that causes gonorrhea, the second most common sexually transmitted infection worldwide. Disease progression, drug discovery, and basic host-pathogen interactions are studied using different approaches, which rely on models ranging from 2D cell culture to complex 3D tissues and animals. In this review, we discuss the models used in N. gonorrhoeae research. We address both in vivo (animal) and in vitro cell culture models, discussing the pros and cons of each and outlining the recent advancements in the field of three-dimensional tissue models. From simple 2D monoculture to complex advanced 3D tissue models, we provide an overview of the relevant methodology and its application. Finally, we discuss future directions in the exciting field of 3D tissue models and how they can be applied for studying the interaction of N. gonorrhoeae with host cells under conditions closely resembling those found at the native sites of infection.

Dynamic generation of power function gradient profiles in a universal microfluidic gradient generator by controlling the inlet flow rates

We report a two-inlet universal microfluidic gradient generator capable of generating gradient profiles of the functional form x^p in the same device by controlling only the inlet flow rates. We have developed an analytical model to predict the inlet flow rates needed to generate a user-specified gradient profile at the outlet. We have validated this model by performing both COMSOL simulations and experiments. Our experiments show an excellent match between the target functions (x^0.33, x¹, x² and x³) and the gradient profiles generated in this device. Unlike the universal gradient generators reported earlier, our device does not require changing the positions of the internal barriers for each new gradient profile, thereby making it easier for the user to operate this device.

Exhausted mature dendritic cells exhibit a slower and less persistent random motility but retain chemotaxis against CCL19

Dendritic cells (DCs), which are immune sentinels in the peripheral tissues, play a number of roles, including patrolling for pathogens, internalising antigens, transporting antigens to the lymph nodes (LNs), interacting with T cells, and secreting cytokines. The well-coordinated migration of DCs under various immunological or inflammatory conditions is therefore essential to ensure an effective immune response. Upon maturation, DCs migrate faster and more persistently than immature DCs (iDCs), which is believed to facilitate CCR7-dependent chemotaxis. It has been reported that lipopolysaccharide-activated DCs produce IL-12 only transiently, and become resistant to further stimulation through exhaustion. However, little is known about the influence of DC exhaustion on cellular motility. Here, we studied the cellular migration of exhausted DCs in tissue-mimicked confined environments. We found that the speed of exhausted matured DCs (xmDCs) decreased significantly compared to active matured DCs (amDCs) and iDCs. In contrast, the speed fluctuation increased compared to that of amDCs and was similar to that of iDCs. In addition, the diffusivity of the xmDCs was significantly lower than that of the amDCs, which implies that DC exhaustion reduces the space exploration ability. Interestingly, CCR7-dependent chemotaxis against CCL19 in xmDCs was not considerably different from that observed in amDCs. Taken together, we report a unique intrinsic cell migration behaviour of xmDCs, which exhibit a slower, less persistent, and less diffusive random motility, which results in the DCs remaining at the site of infection, although a well-preserved CCR7-dependent chemotactic motility is maintained.

Microfluidic Systems to Study Neutrophil Forward and Reverse Migration

During infection, neutrophils are the most abundantly recruited innate immune cells at sites of infection, playing critical roles in the elimination of local infection and healing of the injury. Neutrophils are considered to be short-lived effector cells that undergo cell death at infection sites and in damaged tissues. However, recent in vitro and in vivo evidence suggests that neutrophil behavior is more complex and that they can migrate away from the inflammatory site back into the vasculature following the resolution of inflammation. Microfluidic devices have contributed to an improved understanding of the interaction and behavior of neutrophils ex vivo in 2D and 3D microenvironments. The role of reverse migration and its contribution to the resolution of inflammation remains unclear. In this review, we will provide a summary of the current applications of microfluidic devices to investigate neutrophil behavior and interactions with other immune cells with a focus on forward and reverse migration in neutrophils.

Human Neutrophils Respond to Complement Activation and Inhibition in Microfluidic Devices

Complement activation is key to anti-microbial defenses by directly acting on microbes and indirectly by triggering cellular immune responses. Complement activation may also contribute to the pathogenesis of numerous inflammatory and immunological diseases. Consequently, intense research focuses on developing therapeutics that block pathology-causing complement activation while preserving anti-microbial complement activities. However, the pace of research is slowed down significantly by the limitations of current tools for evaluating complement-targeting therapeutics. Moreover, the effects of potential therapeutic agents on innate immune cells, like neutrophils, are not fully understood. Here, we employ microfluidic assays and measure chemotaxis, phagocytosis, and swarming changes in human neutrophils ex vivo in response to various complement-targeting agents. We show that whereas complement factor 5 (C5) cleavage inhibitor eculizumab blocks all neutrophil anti-microbial functions, newer compounds like the C5 cleavage inhibitor RA101295 and C5a receptor antagonist avacopan inhibit chemotaxis and swarming while preserving neutrophil phagocytosis. These results highlight the utility of microfluidic neutrophil assays in evaluating potential complement-targeting therapeutics.

Directional reorientation of migrating neutrophils is limited by suppression of receptor input signaling at the cell rear through myosin II activity

To migrate efficiently to target locations, cells must integrate receptor inputs while maintaining polarity: a distinct front that leads and a rear that follows. Here we investigate what is necessary to overwrite pre-existing front-rear polarity in neutrophil-like HL60 cells migrating inside straight microfluidic channels. Using subcellular optogenetic receptor activation, we show that receptor inputs can reorient weakly polarized cells, but the rear of strongly polarized cells is refractory to new inputs. Transient stimulation reveals a multi-step repolarization process, confirming that cell rear sensitivity to receptor input is the primary determinant of large-scale directional reversal. We demonstrate that the RhoA/ROCK/myosin II pathway limits the ability of receptor inputs to signal to Cdc42 and reorient migrating neutrophils. We discover that by tuning the phosphorylation of myosin regulatory light chain we can modulate the activity and localization of myosin II and thus the amenability of the cell rear to 'listen' to receptor inputs and respond to directional reprogramming.

Simultaneous biochemical and functional phenotyping of single circulating tumor cells using ultrahigh throughput and recovery microfluidic devices

Profiling circulating tumour cells (CTCs) in cancer patients' blood samples is critical to understand the complex and dynamic nature of metastasis. This task is challenged by the fact that CTCs are not only extremely rare in circulation but also highly heterogeneous in their molecular programs and cellular functions. Here we report a combinational approach for the simultaneous biochemical and functional phenotyping of patient-derived CTCs, using an integrated inertial ferrohydrodynamic cell separation (i²FCS) method and a single-cell microfluidic migration assay. This combinatorial approach offers unique capability to profile CTCs on the basis of their surface expression and migratory characteristics. We achieve this using the i²FCS method that successfully processes whole blood samples in a tumor cell marker and size agnostic manner. The i²FCS method enables an ultrahigh blood sample processing throughput of up to 2 × 10⁵ cells s^-1 with a blood sample flow rate of 60 mL h^-1. Its short processing time (10 minutes for a 10 mL sample), together with a close-to-complete CTC recovery (99.70% recovery rate) and a low WBC contamination (4.07-log depletion rate by removing 99.992% of leukocytes), results in adequate and functional CTCs for subsequent studies in the single-cell migration device. For the first time, we employ this new approach to query CTCs with single-cell resolution in accordance with their expression of phenotypic surface markers and migration properties, revealing the dynamic phenotypes and the existence of a high-motility subpopulation of CTCs in blood samples from metastatic lung cancer patients. This method could be adopted to study the biological and clinical value of invasive CTC phenotypes.

Point-of-critical-care diagnostics for sepsis enabled by multiplexed micro and nanosensing technologies

Sepsis is responsible for the highest economic and mortality burden in critical care settings around the world, prompting the World Health Organization in 2018 to designate it as a global health priority. Despite its high universal prevalence and mortality rate, a disproportionately low amount of sponsored research funding is directed toward diagnosis and treatment of sepsis, when early treatment has been shown to significantly improve survival. Additionally, current technologies and methods are inadequate to provide an accurate and timely diagnosis of septic patients in multiple clinical environments. For improved patient outcomes, a comprehensive immunological evaluation is critical which is comprised of both traditional testing and quantifying recently proposed biomarkers for sepsis. There is an urgent need to develop novel point-of-care, low-cost systems which can accurately stratify patients. These point-of-critical-care sensors should adopt a multiplexed approach utilizing multimodal sensing for heterogenous biomarker detection. For effective multiplexing, the sensors must satisfy criteria including rapid sample to result delivery, low sample volumes for clinical sample sparring, and reduced costs per test. A compendium of currently developed multiplexed micro and nano (M/N)-based diagnostic technologies for potential applications toward sepsis are presented. We have also explored the various biomarkers targeted for sepsis including immune cell morphology changes, circulating proteins, small molecules, and presence of infectious pathogens. An overview of different M/N detection mechanisms are also provided, along with recent advances in related nanotechnologies which have shown improved patient outcomes and perspectives on what future successful technologies may encompass. This article is categorized under: Diagnostic Tools > Biosensing.

Human Blood Serum Induces p38-MAPK- and Hsp27-Dependent Migration Dynamics of Adult Human Cardiac Stem Cells: Single-Cell Analysis via a Microfluidic-Based Cultivation Platform

Simple Summary

Adult human stem cells possess the ability to contribute to endogenous regeneration processes of injured tissue by migrating to specific locations. For stem cell-based clinical applications it is highly important to gain knowledge about the migration behavior of adult human stem cells and the underlying molecular mechanisms of this ability. Human blood serum has been shown to have beneficial effects on other regenerative capacities of adult human stem cells. Within this study we tested the effect of human blood serum on the migration behavior of stem cells from the human heart. We used a microfluidic cultivation device, which allowed us to monitor the living cells and their movement behavior in real time. After addition of human blood serum, the heart stem cells increased their speed of movement and covered distance. Further, we observed that this effect could be diminished by inhibition of a specific kinase, p38-MAPK. Thus, our data suggest beneficial effects of human blood serum on adult human heart stem cells dependent on p38-MAPK. Our study contributes to a deeper understanding of the dynamics of stem cell migration and introduces a new platform to monitor stem cell movement in real time.

Abstract

Migratory capabilities of adult human stem cells are vital for assuring endogenous tissue regeneration and stem cell-based clinical applications. Although human blood serum has been shown to be beneficial for cell migration and proliferation, little is known about its impact on the migratory behavior of cardiac stem cells and underlying signaling pathways. Within this study, we investigated the effects of human blood serum on primary human cardiac stem cells (hCSCs) from the adult heart auricle. On a technical level, we took advantage of a microfluidic cultivation platform, which allowed us to characterize cell morphologies and track migration of single hCSCs via live cell imaging over a period of up to 48 h. Our findings showed a significantly increased migration distance and speed of hCSCs after treatment with human serum compared to control. Exposure of blood serum-stimulated hCSCs to the p38 mitogen-activated protein kinase (p38-MAPK) inhibitor SB239063 resulted in significantly decreased migration. Moreover, we revealed increased phosphorylation of heat shock protein 27 (Hsp27) upon serum treatment, which was diminished by p38-MAPK-inhibition. In summary, we demonstrate human blood serum as a strong inducer of adult human cardiac stem cell migration dependent on p38-MAPK/Hsp27-signalling. Our findings further emphasize the great potential of microfluidic cultivation devices for assessing spatio-temporal migration dynamics of adult human stem cells on a single-cell level.

Neonatal sepsis at point of care

Sepsis, which includes infection followed by inflammation, is one of the leading causes of death among neonates worldwide. The major attribute of this disease process is dysregulated host response to infection leading to organ dysfunction and potentially death. A comprehensive understanding of the host response as well as the pathogen itself are important factors contributing to outcome. Early diagnosis is paramount, as it leads to accurate assessment and improved clinical management. Accordingly, a number of diagnostic platforms have been introduced to assess the presence of blood stream pathogens in septic neonates. Unfortunately, current point-of-care (POC) methods rely on a single parameter/biomarker and thus lack a comprehensive evaluation. The emerging field of biosensing has, however, resulted in the development of a wide range of analytical devices that may be useful at POC. This review discusses currently available methods to screen the inflammatory process in neonatal sepsis. We describe POC sensor-based methods for single platform multi-analyte detection and highlight the latest advances in this evolving technology. Finally, we critically evaluate the applicability of these POC devices clinically for early diagnosis of sepsis in neonates.

Analyzing Inter-Leukocyte Communication and Migration In Vitro: Neutrophils Play an Essential Role in Monocyte Activation During Swarming

Neutrophils are known to be the first responders to infection or injury. However, as inflammation progresses, other leukocytes become increasingly important in inflammation propagation, tissue reconstruction, and inflammation resolution. In recent years, there has been an increase in publications that analyze neutrophil behavior in vitro, but there remains a gap in the literature for in vitro technologies that enable quantitatively measuring interactions between different types of human leukocytes. Here, we used an in vitro platform that mimics inflammation by inducing neutrophil swarming to analyze the behavior of various leukocytes in a swarming setting. Using human peripheral blood leukocytes isolated directly from whole blood, we found that myeloid cells and lymphoid cells had different migratory behaviors. Myeloid cells, which are predominately neutrophils, exhibited swarming behavior. This behavior was not seen with lymphoid cells. We perturbed the peripheral blood leukocyte system by adding exogenous leukotriene B₄ (LTB₄) to the medium. Notably, only the myeloid cell compartment was significantly changed by the addition of LTB₄. Additionally, LTB₄ had no significant impact on myeloid cell migration during the recruitment phase of swarming. To further investigate the myeloid cell compartment, we isolated neutrophils and monocytes to analyze their interaction on the platform. We found that neutrophils increase monocyte migration toward the bioparticle clusters, as measured through speed, chemotactic index, track straightness, and swarm size. These results were confirmed with in vivo mouse experiments, where monocyte accumulation only occurred when neutrophils were present. Additionally, we found that both neutrophils and monocytes release the monocyte chemoattractant proteins CCL2 and CCL3 in the presence of Staphylococcus aureus bioparticles. Furthermore, extracellular vesicles from swarming neutrophils caused monocyte activation. These findings suggest that neutrophils play an essential role in the onset of inflammation not only by sealing off the site of infection or injury, but also by recruiting additional leukocytes to the site.

Bitter taste receptor T2R14 detects quorum sensing molecules from cariogenic Streptococcus mutans and mediates innate immune responses in gingival epithelial cells

Host-pathogen interactions play an important role in defining the outcome of a disease. Recent studies have shown that the bacterial quorum sensing molecules (QSM) can interact with host cell membrane proteins, mainly G protein-coupled receptors (GPCRs), and induce innate immune responses. However, few studies have examined QSM-GPCR interactions and their influence on oral innate immune responses. In this study, we examined the role of bitter taste receptor T2R14 in sensing competence stimulating peptides (CSPs) secreted by cariogenic bacterium Streptococcus mutans and in mediating innate immune responses in gingival epithelial cells (GECs). Transcriptomic and western blot analyses identify T2R14 to be highly expressed in GECs. Our data show that only CSP-1 from S. mutans induces robust intracellular calcium mobilization compared to CSP-2 and CSP-3. By using CRISPR-Cas9, we demonstrate that CSP-1 induced calcium signaling and secretion of cytokines CXCL-8/IL-8, TNF-α, and IL-6 is mediated through T2R14 in GECs. Interestingly, the NF-kB signaling activated by CSP-1 in GECs was independent of T2R14. CSP-1-primed GECs attracted differentiated HL-60 immune cells (dHL-60) and this effect was abolished in T2R14 knock down GECs and also in cells primed with T2R14 antagonist 6-Methoxyflavone (6-MF). Our findings identify S. mutans CSP-1 as a peptide ligand for the T2R family. Our study establishes a novel host-pathogen interaction between cariogenic S. mutans CSP-1 and T2R14 in GECs leading to an innate immune response. Collectively, these findings suggest T2Rs as potential therapeutic targets to modulate innate immune responses upon oral bacterial infections.

Immobilisation of CXCL8 gradients in microfluidic devices for migration experiments

The release of inflammatory chemokines leads to the formation of chemokine gradients that result in the directed migration of immune cells to the site of injury. In this process, cells respond to soluble gradients (chemotaxis) as well as to immobilised gradients (haptotaxis). Surface-bound chemokine gradients are mostly presented by endothelial cells and supported by glycosaminoglycans (GAGs), such as heparan sulfate, involving the GAG binding site of chemokines. Microfluidic devices have been used to analyse cell migration along soluble chemokine gradients, as these devices allow the generation of stable gradients with resolutions in the range of microns. To immobilise well-controlled soluble gradients of interleukin-8 (CXCL8), an inflammatory chemokine, we developed a simple procedure using a heparin-coated PDMS-microfluidic device. We used these immobilised gradients for migration experiments with CXCL8-responsive THP-1 cells and confirmed directed cell migration. This setup might be useful for the examination of factors that may alter chemotaxis and haptotaxis as well as synergistic and antagonistic effects of other soluble and immobilised chemokines.

Multiplexed end-point microfluidic chemotaxis assay using centrifugal alignment

A fundamental challenge to multiplexing microfluidic chemotaxis assays at scale is the requirement for time-lapse imaging to continuously track migrating cells. Drug testing and drug screening applications require the ability to perform hundreds of experiments in parallel, which is not feasible for assays that require continuous imaging. To address this limitation, end-point chemotaxis assays have been developed using fluid flow to align cells in traps or sieves prior to cell migration. However, these methods require precisely controlled fluid flow to transport cells to the correct location without undesirable mechanical stress, which introduce significant set up time and design complexity. Here, we describe a microfluidic device that eliminates the need for precise flow control by using centrifugation to align cells at a common starting point. A chemoattractant gradient is then formed using passive diffusion prior to chemotaxis in an incubated environment. This approach provides a simple and scalable approach to multiplexed chemotaxis assays. Centrifugal alignment is also insensitive to cell geometry, enabling this approach to be compatible with primary cell samples that are often heterogeneous. We demonstrate the capability of this approach by assessing chemotaxis of primary neutrophils in response to an fMLP (N-formyl-met-leu-phe) gradient. Our results show that cell alignment by centrifugation offers a potential avenue to develop scalable end-point multiplexed microfluidic chemotaxis assays.

Establishment of a scalable microfluidic assay for characterization of population-based neutrophil chemotaxis

BACKGROUND

Regulation of neutrophil chemotaxis and activation plays crucial roles in immunity, and dysregulated neutrophil responses can lead to pathology as seen in neutrophilic asthma. Neutrophil recruitment is key for initiating immune defense and inflammation, and its modulation is a promising therapeutic target. Microfluidic technology is an attractive tool for characterization of neutrophil migration. Compared to transwell assays, microfluidic approaches could offer several advantages, including precis e control of defined chemokine gradients in space and time, automated quantitative analysis of chemotaxis, and high throughput.

METHODS

We established a microfluidic device for fully automated, quantitative assessment of neutrophil chemotaxis. Freshly isolated mouse neutrophils from bone marrow or human neutrophils from peripheral blood were assessed in real time using an epifluorescence microscope for their migration toward the potent chemoattractants C-X-C-motif ligand 2 (CXCL2) and CXCL8, without or with interleukin-4 (IL-4) pre-incubation.

RESULTS

Our microfluidic device allowed the precise and reproducible determination of the optimal CXCL2 and CXCL8 concentrations for mouse and human neutrophil chemotaxis, respectively. Furthermore, our microfluidic assay was able to measure the equilibrium and real-time dynamic effects of specific modulators of neutrophil chemotaxis. We demonstrated this concept by showing that IL-4 receptor signaling in mouse and human neutrophils inhibited their migration toward CXCL2 and CXCL8, respectively, and this inhibition was time-dependent.

CONCLUSION

Collectively, our microfluidic device shows several advantages over traditional transwell migration assays and its design is amenable to future integration into multiplexed high-throughput platforms for screening of molecules that modulate the chemotaxis of different immune cells.

Neutrophil-like HL-60 cells expressing only GFP-tagged β-actin exhibit nearly normal motility

Observations of actin dynamics in living cells using fluorescence microscopy have been foundational in the exploration of the mechanisms underlying cell migration. We used CRISPR/Cas9 gene editing to generate neutrophil‐like HL‐60 cell lines expressing GFP‐β‐actin from the endogenous locus (ACTB). In light of many previous reports outlining functional deficiencies of labeled actin, we anticipated that HL‐60 cells would only tolerate a monoallelic edit, as biallelic edited cells would produce no normal β‐actin. Surprisingly, we recovered viable monoallelic GFP‐β‐actin cells as well as biallelic edited GFP‐β‐actin cells, in which one copy of the ACTB gene is silenced and the other contains the GFP tag. Furthermore, the edited cells migrate with similar speeds and persistence as unmodified cells in a variety of motility assays, and have nearly normal cell shapes. These results might partially be explained by our observation that GFP‐β‐actin incorporates into the F‐actin network in biallelic edited cells at similar efficiencies as normal β‐actin in unedited cells. Additionally, the edited cells significantly upregulate γ‐actin, perhaps helping to compensate for the loss of normal β‐actin. Interestingly, biallelic edited cells have only modest changes in global gene expression relative to the monoallelic line, as measured by RNA sequencing. While monoallelic edited cells downregulate expression of the tagged allele and are thus only weakly fluorescent, biallelic edited cells are quite bright and well‐suited for live cell microscopy. The nondisruptive phenotype and direct interpretability of this fluorescent tagging approach make it a promising tool for studying actin dynamics in these rapidly migrating and highly phagocytic cells.

Efficient Front-Rear Coupling in Neutrophil Chemotaxis by Dynamic Myosin II Localization

Efficient chemotaxis requires rapid coordination between different parts of the cell in response to changing directional cues. Here, we investigate the mechanism of front-rear coordination in chemotactic neutrophils. We find that changes in the protrusion rate at the cell front are instantaneously coupled to changes in retraction at the cell rear, while myosin II accumulation at the rear exhibits a reproducible 9-15-s lag. In turning cells, myosin II exhibits dynamic side-to-side relocalization at the cell rear in response to turning of the leading edge and facilitates efficient turning by rapidly re-orienting the rear. These manifestations of front-rear coupling can be explained by a simple quantitative model incorporating reversible actin-myosin interactions with a rearward-flowing actin network. Finally, the system can be tuned by the degree of myosin regulatory light chain (MRLC) phosphorylation, which appears to be set in an optimal range to balance persistence of movement and turning ability.

Ex Vivo Human Neutrophil Swarming Against Live Microbial Targets

Neutrophils often communicate with each other and coordinate their actions to seal off large sites of injury and infection that individual neutrophils could not cover. The concerted actions of neutrophils are essential for the expeditious protection of healthy tissues from wounds and microbes. These processes, collectively known as swarming, are typically studied in vivo in mice. However, these studies are low throughput and their relevance to human disease is limited. Recently, new tools have been developed for the study of human neutrophil swarming ex vivo. The emergent microscale swarming assays are providing significant insights into the molecular mediators of swarming. By enabling the direct study of human cells, these assays also shed new light on human diseases and host responses against infections. Here, we describe a robust technique for manufacturing microscale swarming arrays with live microbial targets (e.g., clusters of Candida albicans). These arrays allow for the direct, precise, and efficient interrogation of the antimicrobial functions of human swarming against a variety of targets.

A C-terminal CXCL8 peptide based on chemokine-glycosaminoglycan interactions reduces neutrophil adhesion and migration during inflammation

Leucocyte recruitment is critical during many acute and chronic inflammatory diseases. Chemokines are key mediators of leucocyte recruitment during the inflammatory response, by signalling through specific chemokine G-protein-coupled receptors (GPCRs). In addition, chemokines interact with cell-surface glycosaminoglycans (GAGs) to generate a chemotactic gradient. The chemokine interleukin-8/CXCL8, a prototypical neutrophil chemoattractant, is characterized by a long, highly positively charged GAG-binding C-terminal region, absent in most other chemokines. To examine whether the CXCL8 C-terminal peptide has a modulatory role in GAG binding during neutrophil recruitment, we synthesized the wild-type CXCL8 C-terminal [CXCL8 (54-72)] (Peptide 1), a peptide with a substitution of glutamic acid (E) 70 with lysine (K) (Peptide 2) to increase positive charge; and also, a scrambled sequence peptide (Peptide 3). Surface plasmon resonance showed that Peptide 1, corresponding to the core CXCL8 GAG-binding region, binds to GAG but Peptide 2 binding was detected at lower concentrations. In the absence of cellular GAG, the peptides did not affect CXCL8-induced calcium signalling or neutrophil chemotaxis along a diffusion gradient, suggesting no effect on GPCR binding. All peptides equally inhibited neutrophil adhesion to endothelial cells under physiological flow conditions. Peptide 2, with its greater positive charge and binding to polyanionic GAG, inhibited CXCL8-induced neutrophil transendothelial migration. Our studies suggest that the E70K CXCL8 peptide, may serve as a lead molecule for further development of therapeutic inhibitors of neutrophil-mediated inflammation based on modulation of chemokine-GAG binding.

Mimicry of Central-Peripheral Immunity in Alzheimer's Disease and Discovery of Neurodegenerative Roles in Neutrophil

Neuroinflammatory roles of central innate immunity in brain parenchyma are well-regarded in the progression of neurodegenerative disorders including Alzheimer's disease (AD), however, the roles of peripheral immunity in central nervous system (CNS) diseases are less clear. Here, we created a microfluidic environment of human AD brains: microglial neuroinflammation induced by soluble amyloid-beta (Abeta), a signature molecule in AD and employed the environment to investigate the roles of neutrophils through the central-peripheral innate immunity crosstalk. We observed that soluble Abeta-activated human microglial cells produced chemoattractants for neutrophils including IL6, IL8, CCL2, CCL3/4, CCL5 and consequently induced reliable recruitment of human neutrophils. Particularly, we validated the discernable chemo-attractive roles of IL6, IL8, and CCL2 for neutrophils by interrupting the recruitment with neutralizing antibodies. Upon recruitment, microglia-neutrophils interaction results in the production of inflammatory mediators such as MIF and IL2, which are known to up-regulate neuroinflammation in AD. We envision that targeting the crosstalk between central-peripheral immune community is a potential strategy to reduce immunological burdens in other neuroinflammatory CNS diseases.

Identification of bioactive metabolites using activity metabolomics

The metabolome, the collection of small-molecule chemical entities involved in metabolism, has traditionally been studied with the aim of identifying biomarkers in the diagnosis and prediction of disease. However, the value of metabolome analysis (metabolomics) has been redefined from a simple biomarker identification tool to a technology for the discovery of active drivers of biological processes. It is now clear that the metabolome affects cellular physiology through modulation of other 'omics' levels, including the genome, epigenome, transcriptome and proteome. In this Review, we focus on recent progress in using metabolomics to understand how the metabolome influences other omics and, by extension, to reveal the active role of metabolites in physiology and disease. This concept of utilizing metabolomics to perform activity screens to identify biologically active metabolites - which we term activity metabolomics - is already having a broad impact on biology.

T cell migration in microchannels densely packed with T cells

T cells migrate diverse microenvironments of the body to mount antigen-specific immune responses. T cell activation, a key initial process for antigen-specific immune responses, occur in secondary lymphoid organs such as spleens and lymph nodes where high density of T cells migrates rapidly through the reticular networks formed by stromal cells. In vitro model system recapitulating key characteristics of secondary lymphoid organs, confined spaces densely packed with rapidly migrating cells, would be useful to investigate mechanisms of T cell migration. In this study, we devised a method to fabricate microchannels densely packed with T cells. Microchannel arrays with fixed height (4 μm) and length (1.5 mm) and various widths (15~80 μm) were fabricated in between trapezoid-shaped reservoirs that facilitated T cell sedimentation near microchannel entries. Microchannel surface chemistry and filling time were optimized to achieve high packing density (0.89) of T cell filling within microchannels. Particle image velocimetry (PIV) analysis method was employed to extract velocity field of microchannels densely packed with T cells. Using velocity field information, various motility parameters were further evaluated to quantitatively assess the effects of microchannel width and media tonicity on T cell motility within cell dense microenvironments.

Super-Low Dose Lipopolysaccharide Dysregulates Neutrophil Migratory Decision-Making

Neutrophils are the first responders to infection and play a pivotal role in many inflammatory diseases, including sepsis. Recent studies have shown that lipopolysaccharide (LPS), a classical pattern recognition molecule, dynamically programs innate immune responses. In this study, we show that pre-treatment with super-low levels of LPS [1 ng/mL] significantly dysregulate neutrophil migratory phenotypes, including spontaneous migration and altering neutrophil decision-making. To quantify neutrophil migratory decision-making with single-cell resolution, we developed a novel microfluidic competitive chemotaxis-chip (μC³) that exposes cells in a central channel to competing chemoattractant gradients. In this reductionist approach, we use two chemoattractants: a pro-resolution (N-Formyl-Met-Leu-Phe, fMLP) and pro-inflammatory (Leukotriene B₄, LTB₄) chemoattractant to model how a neutrophil makes a decision to move toward an end target chemoattractant (e.g., bacterial infection) vs. an intermediary chemoattractant (e.g., inflammatory signal). We demonstrate that naïve neutrophils migrate toward the primary end target signal in higher percentages than toward the secondary intermediary signal. As expected, we found that training with high dose LPS [100 ng/mL] influences a higher percentage of neutrophils to migrate toward the end target signal, while reducing the percentage of neutrophils that migrate toward the intermediary signal. Surprisingly, super-low dose LPS [1 ng/mL] significantly changes the ratios of migrating cells and an increased percentage of cells migrate toward the intermediary signal. Significantly, there was also an increase in the numbers of spontaneously migrating neutrophils after treatment with super-low dose LPS. These results shed light onto the directional migratory decision-making of neutrophils exposed to inflammatory training signals. Understanding these mechanisms may lead to the development of pro-resolution therapies that correct the neutrophil compass and reduce off-target organ damage.

Analysis of Leukocyte Behaviors on Microfluidic Chips

The orchestration of massive leukocytes in the immune system protects humans from invading pathogens and abnormal cells in the body. So far, researches focusing on leukocyte behaviors are performed based on both in vivo and in vitro models. The in vivo animal models are usually less controllable due to their extreme complexity and nonignorable species issue. Therefore, many researchers turn to in vitro models. With the advances in micro/nanofabrication, the microfluidic chip has emerged as a novel platform for model construction in multiple biomedical research fields. Specifically, the microfluidic chip is used to study leukocyte behaviors, due to its incomparable advantages in high throughput, precise control, and flexible integration. Moreover, the small size of the microstructures on the microfluidic chip can better mimic the native microenvironment of leukocytes, which contributes to a more reliable recapitulation. Herein are reviewed the recent advances in microfluidic chip-based leukocyte behavior analysis to provide an overview of this field. Detailed discussions are specifically focused on host defense against pathogens, immunodiagnosis, and immunotherapy studies on microfluidic chips. Finally, the current technical challenges are discussed, as well as possible innovations in this field to improve the related applications.

Microfluidic Platform to Quantify Neutrophil Migratory Decision-Making

Neutrophils are the most abundant leukocytes in blood, serving as the first line of host defense in tissue damage and infections. Upon activation by chemokines released from pathogens or injured tissues, neutrophils migrate through complex tissue microenvironments toward sites of infections along the chemokine gradients, in a process named chemotaxis. However, current methods for measuring neutrophil chemotaxis require large volumes of blood and are often bulk, endpoint measurements. To address the need for rapid and robust assays, we engineered a novel dual gradient microfluidic platform that precisely quantifies neutrophil migratory decision-making with high temporal resolution. Here, we present a protocol to measure neutrophil migratory phenotypes (velocity, directionality) with single-cell resolution.

Semaphorin 3F and Netrin-1: The Novel Function as a Regulator of Tumor Microenvironment

Axon guidance molecules play an important role in regulating proper neuronal networking during neuronal development. They also have non-neuronal properties, which include angiogenesis, inflammation, and tumor development. Semaphorin 3F (SEMA3F), a member of the class 3 semaphorins, was initially identified as an axon guidance factor, that repels axons and collapses growth cones. However, SEMA3F has similar effects on endothelial cells (ECs) and tumor cells. In this review, we discuss the novel molecular mechanisms underlying SEMA3F activity in vascular and tumor biology. Recent evidence suggests that SEMA3F functions as a PI3K-Akt-mTOR inhibitor in mammalian cells, including T cells, ECs, and tumor cells. Therefore, SEMA3F may have broad therapeutic implications. We also discuss the key role of axon guidance molecules as regulators of the tumor microenvironment. Netrin-1, a chemoattractant factor in the neuronal system, promotes tumor progression by enhancing angiogenesis and metastasis. Moreover, our recent studies demonstrate that netrin-1/neogenin interactions augment CD4+ T cell chemokinesis and elicit pro-inflammatory responses, suggesting that netrin-1 plays a key role in modulating the function of a tumor and its surrounding cells in the tumor microenvironment. Overall, this review focuses on SEMA3F and netrin-1 signaling mechanisms to understand the diverse biological functions of axon guidance molecules.

Progressive mechanical confinement of chemotactic neutrophils induces arrest, oscillations, and retrotaxis

Neutrophils reach the sites of inflammation and infection in a timely manner by navigating efficiently through mechanically complex interstitial spaces, following the guidance of chemical gradients. However, our understanding of how neutrophils that follow chemical cues overcome mechanical obstacles in their path is restricted by the limitations of current experimental systems. Observations in vivo provide limited insights due to the complexity of the tissue environment. Here, we developed microfluidic devices to study the effect of progressive mechanical confinement on the migration patterns of human neutrophils toward chemical attractants. Using these devices, we identified four migration patterns: arrest, oscillation, retrotaxis, and persistent migration. The proportion of these migration patterns is different in patients receiving immunosuppressant treatments after kidney transplant, patients in critical care, and neonatal patients with infections and is distinct from that in healthy donors. The occurrence of these migration patterns is independent of the nuclear lobe number of the neutrophils and depends on the integrity of their cytoskeletal components. Our study highlights the important role of mechanical cues in moving neutrophils and suggests the mechanical constriction-induced migration patterns as potential markers for infection and inflammation.

Large-scale patterning of living colloids for dynamic studies of neutrophil-microbe interactions

Neutrophils are the first white blood cells to respond to microbes and to limit their invasion of the body. However, the growth of the microbes into colonies often challenges the neutrophils ability to contain them. To study the interactions between neutrophils and microbial colonies, we designed an assay for arranging microbes in clusters of controlled size (i.e. living colloids). The patterned microbes in the living colloid are mechanically trapped inside the wells and fully accessible to neutrophils. Using the assay, we studied the interactions between human neutrophils and Candida albicans and Staphylococcus aureus, two common human pathogens. We also probed the susceptibility of C. albicans colloids to caspofungin, a common antifungal drug.

Matrix elasticity regulates mesenchymal stem cell chemotaxis

Efficient homing of human mesenchymal stem cells (hMSCs) is likely to be dictated by a combination of physical and chemical factors present in the microenvironment. However, crosstalk between the physical and chemical cues remains incompletely understood. Here, we address this question by probing the efficiency of epidermal growth factor (EGF)-induced hMSC chemotaxis on substrates of varying stiffness (3, 30 and 600 kPa) inside a polydimethylsiloxane (PDMS) microfluidic device. Chemotactic speed was found to be the sum of a stiffness-dependent component and a chemokine concentration-dependent component. While the stiffness-dependent component scaled inversely with stiffness, the chemotactic component was independent of stiffness. Faster chemotaxis on the softest 3 kPa substrates is attributed to a combination of weaker adhesions and higher protrusion rate. While chemotaxis was mildly sensitive to contractility inhibitors, suppression of chemotaxis upon actin depolymerization demonstrates the role of actin-mediated protrusions in driving chemotaxis. In addition to highlighting the collective influence of physical and chemical cues in chemotactic migration, our results suggest that hMSC homing is more efficient on softer substrates.

A Novel Microdevice for Rapid Neutrophil Purification and Phenotyping in Type 2 Diabetes Mellitus

Neutrophil dysfunction is strongly linked to type 2 diabetes mellitus (T2DM) pathophysiology, but the prognostic potential of neutrophil biomarkers remains largely unexplored due to arduous leukocyte isolation methods. Herein, a novel integrated microdevice is reported for single-step neutrophil sorting and phenotyping (chemotaxis and formation of neutrophil extracellular traps (NETosis)) using small blood volumes (fingerprick). Untouched neutrophils are purified on-chip from whole blood directly using biomimetic cell margination and affinity-based capture, and are exposed to preloaded chemoattractant or NETosis stimulant to initiate chemotaxis or NETosis, respectively. Device performance is first characterized using healthy and in vitro inflamed blood samples (tumor necrosis factor alpha, high glucose), followed by clinical risk stratification in a cohort of subjects with T2DM. Interestingly, "high-risk" T2DM patients characterized by severe chemotaxis impairment reveal significantly higher C-reactive protein levels and poor lipid metabolism characteristics as compared to "low-risk" subjects, and their neutrophil chemotaxis responses can be mitigated after in vitro metformin treatment. Overall, this unique and user-friendly microfluidics immune health profiling strategy can significantly aid the quantification of chemotaxis and NETosis in clinical settings, and be further translated into a tool for risk stratification and precision medicine methods in subjects with metabolic diseases such as T2DM.