Cell identification and isolation on the basis of cytokine secretion: a novel tool for investigating immune responses

High-precision screening and sorting of double emulsion droplets

Mounting evidence suggests that cell populations are extremely heterogeneous, with individual cells fulfilling different roles within the population. Flow cytometry (FC) is a high-throughput tool for single-cell analysis that works at high optical resolution. Sub-populations with unique properties can be screened, isolated and sorted through fluorescence-activated cell sorting (FACS), using intracellular fluorescent products or surface-tagged fluorescent products of interest. However, traditional FC and FACS methods cannot identify or isolate cells that secrete extracellular products of interest. Double emulsion (DE) droplets are an innovative approach to retaining these extracellular products so cells producing them can be identified and isolated with FC and FACS. The water-in-oil-in-water structure makes DE droplets compatible with the sheath flow of flow cytometry. Single cells can be encapsulated with other reagents into DEs, which act as pico-reactors. These droplets allow biological activities to take place while allowing for cell cultivation monitoring, rare mutant identification, and cellular events characterization. However, using DEs in FACS presents technical challenges, including rupture of DEs, poor accuracy and low sorting efficiency. This study presents high-performance sorting using fluorescent beads (as simulants for cells). This study aims to guide researchers in the use of DE-based flow cytometry, offering insights into how to resolve the technical difficulties associated with DE-based screening and sorting using FC.

Identification of druggable regulators of cell secretion via a kinome-wide screen and high-throughput immunomagnetic cell sorting

The identification of genetic regulators of cell secretions is challenging because it requires the sorting of a large number of cells according to their secretion patterns. Here we report the development and applicability of a high-throughput microfluidic method for the analysis of the secretion levels of large populations of immune cells. The method is linked with a kinome-wide loss-of-function CRISPR screen, immunomagnetically sorting the cells according to their secretion levels, and the sequencing of their genomes to identify key genetic modifiers of cell secretion. We used the method, which we validated against flow cytometry for cytokines secreted from primary mouse CD4+ (cluster of differentiation 4-positive) T cells, to discover a subgroup of highly co-expressed kinase-coding genes that regulate interferon-gamma secretion by these cells. We validated the function of the kinases identified using RNA interference, CRISPR knockouts and kinase inhibitors and confirmed the druggability of selected kinases via the administration of a kinase inhibitor in an animal model of colitis. The technique may facilitate the discovery of regulatory mechanisms for immune-cell activation and of therapeutic targets for autoimmune diseases.

Droplet flow cytometry for single-cell analysis

The interrogation of single cells has revolutionised biology and medicine by providing crucial unparalleled insights into cell-to-cell heterogeneity. Flow cytometry (including fluorescence-activated cell sorting) is one of the most versatile and high-throughput approaches for single-cell analysis by detecting multiple fluorescence parameters of individual cells in aqueous suspension as they flow past through a focus of excitation lasers. However, this approach relies on the expression of cell surface and intracellular biomarkers, which inevitably lacks spatial and temporal phenotypes and activities of cells, such as secreted proteins, extracellular metabolite production, and proliferation. Droplet microfluidics has recently emerged as a powerful tool for the encapsulation and manipulation of thousands to millions of individual cells within pico-litre microdroplets. Integrating flow cytometry with microdroplet architectures surrounded by aqueous solutions (e.g., water-in-oil-in-water (W/O/W) double emulsion and hydrogel droplets) opens avenues for new cellular assays linking cell phenotypes to genotypes at the single-cell level. In this review, we discuss the capabilities and applications of droplet flow cytometry (DFC). This unique technique uses standard commercially available flow cytometry instruments to characterise or select individual microdroplets containing single cells of interest. We explore current challenges associated with DFC and present our visions for future development.

High-Throughput Measurements of Intra-Cellular and Secreted Cytokine from Single Spheroids Using Anchored Microfluidic Droplets

While many single-cell approaches have been developed to measure secretions from anchorage-independent cells, these protocols cannot be applied to adherent cells, especially when these cells require to be cultured in 3D formats. Here, a platform to measure secretions from individual spheroids of human mesenchymal stem cells, cultured within microfluidic droplets is introduced. The platform allows to quantify the secretions from hundreds of individual spheroids in each device, by using a secondary droplet to bring functionalized micro-beads in proximity to each spheroid. Vascular endothelial growth factor (VEGF-A) is measured on and a broad distribution of secretion levels within the population of spheroids is observed. The intra-cellular level of VEGF-A on each spheroid, measured through immuno-staining, correlates well with the extra-cellular measurement, indicating that the heterogeneities observed at the spheroid level result from variations at the intra-cellular level. Further, the molecular accumulation within the droplets is modeled and it is found that physical confinement is crucial for measurements of protein secretions. The model predicts that the time to achieve a measurement scales with droplet volume. These first measurements of secretions from individual spheroids provide several new biological and technological insights.

A Nanoparticle-Based Affinity Sensor that Identifies and Selects Highly Cytokine-Secreting Cells

We developed a universal method termed OnCELISA to detect cytokine secretion from individual cells by applying a capture technology on the cell membrane. OnCELISA uses fluorescent magnetic nanoparticles as assay reporters that enable detection on a single-cell level in microscopy and flow cytometry and fluorimetry in cell ensembles. This system is flexible and can be modified to detect different cytokines from a broad range of cytokine-secreting cells. Using OnCELISA we have been able to select and sort highly cytokine-secreting cells and identify cytokine-secreting expression profiles of different cell populations in vitro and ex vivo. We show that this system can be used for ultrasensitive monitoring of cytokines in the complex biological environment of atherosclerosis that contains multiple cell types. The ability to identify and select cell populations based on their cytokine expression characteristics is valuable in a host of applications that require the monitoring of disease progression.

Challenges in Developing Protein Secretion Assays at a Single-Cell Level

In addition to direct physical interactions between/among cells, the secretion of humoral factors from living cells is a critical process for cell-cell communications. A well-known extracellular signaling event is mediated by immune cell cytokines/chemokines. Because cell-cell communication is crucial in immune cell sociology, protein secretion assays first attracted a broad range of immunology interests. Now that we have entered an era of systems biology, cell-cell interactions mediated by secreted molecules should be revisited to understand the dynamics and homeostasis of the cell society as a whole. Of more importance, recent advances in detection and microfluidics technologies enable us to monitor protein secretion in real time rather than as a snapshot from the past, which gives us an opportunity to more deeply understand the logic of mammalian cell sociology. This chapter reviews the recent progress in and future direction of protein secretion assays, particularly from a mammalian cell sociology viewpoint.

The Anti-Inflammatory Effect and Structure of EPCP1-2 from Crypthecodinium cohnii via Modulation of TLR4-NF-κB Pathways in LPS-Induced RAW 264.7 Cells

Exopolysaccharide from Crypthecodinium cohnii (EPCP1-2) is a marine exopolysaccharide that evidences a variety of biological activities. We isolated a neutral polysaccharide from the fermentation liquid of Crypthecodinium cohnii (CP). In this study, a polysaccharide that is derived from Crypthecodinium cohnii were analyzed and its anti-inflammatory effect was evaluated on protein expression of toll-like receptor 4 and nuclear factor κB pathways in macrophages. The structural characteristics of EPCP1-2 were characterized by GC (gas chromatography) and GC-MS (gas Chromatography-Mass Spectrometer) analyses. The molecular weight was about 82.5 kDa. The main chain of EPCP1-2 consisted of (1→6)-linked mannopyranosyl, (1→6)-linked glucopyranosyl, branched-chain consisted of (1→3,6)-linked galactopyranosyl and terminal consisted of t-l-Rhapyranosyl. The in vitro anti-inflammatory activity was representated through assay of proliferation rate, pro-inflammatory factor (NO) and expressions of proteins on RAW 264.7, the macrophage cell line. The results revealed that EPCP1-2 exhibited significant anti-inflammatory activity by regulating the expression of toll-like receptor 4, mitogen-activated protein kinases, and Nuclear Factor-κB protein.

Protein adsorption in microengraving immunoassays

Microengraving is a novel immunoassay forcharacterizing multiple protein secretions from single cells. During the immunoassay, characteristic diffusion and kinetic time scales τD and τK determine the time for molecular diffusion of proteins secreted from the activated single lymphocytes and subsequent binding onto the glass slide surface respectively. Our results demonstrate that molecular diffusion plays important roles in the early stage of protein adsorption dynamics which shifts to a kinetic controlled mechanism in the later stage. Similar dynamic pathways are observed for protein adsorption with significantly fast rates and rapid shifts in transport mechanisms when C0* is increased a hundred times from 0.313 to 31.3. Theoretical adsorption isotherms follow the trend of experimentally obtained data. Adsorption isotherms indicate that amount of proteins secreted from individual cells and subsequently captured on a clean glass slide surface increases monotonically with time. Our study directly validates that protein secretion rates can be quantified by the microengraving immunoassay. This will enable us to apply microengraving immunoassays to quantify secretion rates from 10⁴–10⁵ single cells in parallel, screen antigen-specific cells with the highest secretion rate for clonal expansion and quantitatively reveal cellular heterogeneity within a small cell sample.

A universal nanoparticle cell secretion capture assay

Secreted proteins play an important role in intercellular interactions, especially between cells of the immune system. Currently, there is no universal assay that allows a simple noninvasive identification and isolation of cells based on their secretion of various products. We have developed such a method. Our method is based on the targeting, to the cell surface, of heterofunctional nanoparticles coupled to a cell surface-specific antibody and to a secreted protein-specific antibody, which captures the secreted protein on the surface of the producing cell. Importantly, this method does not compromise cellviability and is compatible with further culture and expansion of the secreting cells.

Multidimensional analysis of the frequencies and rates of cytokine secretion from single cells by quantitative microengraving

The large diversity of cells that comprise the human immune system requires methods that can resolve the individual contributions of specific subsets to an immunological response. Microengraving is process that uses a dense, elastomeric array of microwells to generate microarrays of proteins secreted from large numbers of individual live cells (approximately 10(4)-10(5) cells/assay). In this paper, we describe an approach based on this technology to quantify the rates of secretion from single immune cells. Numerical simulations of the microengraving process indicated an operating regime between 30 min-4 h that permits quantitative analysis of the rates of secretion. Through experimental validation, we demonstrate that microengraving can provide quantitative measurements of both the frequencies and the distribution in rates of secretion for up to four cytokines simultaneously released from individual viable primary immune cells. The experimental limits of detection ranged from 0.5 to 4 molecules/s for IL-6, IL-17, IFNgamma, IL-2, and TNFalpha. These multidimensional measures resolve the number and intensities of responses by cells exposed to stimuli with greater sensitivity than single-parameter assays for cytokine release. We show that cells from different donors exhibit distinct responses based on both the frequency and magnitude of cytokine secretion when stimulated under different activating conditions. Primary T cells with specific profiles of secretion can also be recovered after microengraving for subsequent expansion in vitro. These examples demonstrate the utility of quantitative, multidimensional profiles of single cells for analyzing the diversity and dynamics of immune responses in vitro and for identifying rare cells from clinical samples.

MRI characterization of agarose gel micro-droplets at acute time-points within the rabbit lumbar muscle

Agarose gel micro-droplets supplemented with provisional matrix proteins have been shown to enhance encapsulated cell survival for cell therapy applications. This study evaluated micro-droplet T(1) and T(2) relaxation on a 1.5 T clinical MRI scanner to guide the optimization of encapsulated cell delivery to intermediate-sized animals. Preliminary in vitro experiments using encapsulated human blood-derived endothelial progenitor cells (EPCs) documented a negligible impact of EPC encapsulation on agarose micro-droplet T(1) and T(2) relaxation, even following transient immersion in 2.3 mm Gd-DTPA. Furthermore, Gd-DTPA immersion did not adversely impact encapsulated cell viability. These results allowed for efficient pre-clinical methodological development using direct injections into the rabbit lumbar region of agarose droplets without cells (n=6). At time-points to 6 h, in vivo injection sites displayed elevated T(2) and T(1) (1.8%: DeltaT(2)=53+/-28%, DeltaT(1)=50+/-25%, n=13; 2.5%: DeltaT(2)=41+/-10%, DeltaT(1)=41+/-26%, n=11). Rapid imaging sequences displayed high conspicuity at sites of Gd-DTPA-immersed capsule injection, which persisted for less than 4 h. Therefore, basic differences of micro-droplet T(1) and T(2) when compared to tissue provide a platform for acute tracking of encapsulated cell fate. Transient Gd-DTPA encapsulation accentuates T(1) differences.

The selection of high-producing cell lines using flow cytometry and cell sorting

The selection of high-producing cell lines is usually time-consuming and labour-intensive. Following transfection, high-producing cells are selected using limiting dilution cloning to prevent non- and low-producing cells from outgrowing high-producing cells, a process that normally takes > 3 months. During this time, the cells have to be screened occasionally to ensure stability of the selected clone. Several new methods for selecting and screening cells using flow cytometry and cell sorting have recently been developed; these include gel microdrop technology, which encapsulates the cells in gelatine beads, and matrix-based secretion assays. This paper reviews these techniques for selecting high-producing cell lines and isolating rare cells.

Inhibitory effects of eutigosides isolated fromEurya emarginata on the inflammatory mediators in RAW264.7 cells

The anti-inflammatory activity of Eurya emarginata (Thumb) Makino, of which leaves have been traditionally used to treat ulcers or diuretic in Jeju Island, has been investigated in the present study. Through the phytochemical study from the methanol extract of E. emaginiata, eutigosides B and C were isolated as the active components. Sseveral inflammatory markers including TNF-alpha, IL-1beta, IL-6, NO, iNOS, and COX-2 were examined. Eutigosides B and C potentially inhibited production of pro-inflammatory cytokines (IL-6 and TNF-alpha) in a dose-dependent manner. Additionally, the intracellular contents of iNOS protein were markedly decreased after treatment with eutigosides B and C. The inhibition of iNOS activity was correlated with the decrease in nitrite levels. These results suggest that eutigoside B and C from E. emarginata may have anti-inflammatory activity through the inhibition of pro-inflammatory cytokines (TNF-alpha and IL-6), iNOS and COX-2.

Thiophenes and furans derivatives: a new class of potential pharmacological agents

A new class of potential pharmacological thiophenes and furans compounds has been prepared. The obtained thiophenes and furans derivatives were screened for anti-inflammatory, antinociceptive and antioxidant activity in rats. In vitro hepatic ALA-D activity was also evaluated. Thiophene 2 exhibited higher anti-inflammatory effect than thiophenes 1 and 3. However, compound 1 demonstrated lower IC(50) for lipid peroxidation than 2 and 3 in liver and brain. Furan compounds 4-6 presented similar anti-inflammatory activity. The acetylenic furans 4 and 5 inhibited scarcely lipid peroxidation at low concentration as 10 μM. Conversely, furan compound 6 was the most effective against lipid peroxidation in liver. Furans 4 and 5 inhibited lipid peroxidation, in brain, only in high concentrations. In contrast, furan 6 protected (90%) against lipid peroxidation at 10 μM. Thiophene 1 was devoid of anti-inflammatory activity but was efficient in reducing acetic acid-induced constriction. Conversely, it analogue furan 4 presented anti-inflammatory and antinociceptive activity. Thiophene and furan inhibited hepatic ALA-D only at high concentrations. All compounds displayed antioxidant activity however the anti-inflammatory activity is not related to antioxidant potential.

Isolation of Rare Isotype Switch Variants in Hybridoma Cell Lines Using an Agarose Gel Microdrop-Based Protein Secretion Assay

Using gel microdrop (GMD) encapsulation technology and fluorescence-activated cell storing (FACS), we have developed a rapid, sensitive, and reliable method for discriminating and recovering rare isotypic switch variants in hybridoma cell lines. Using the GMD-based IgSwitch assay, a novel approach for isolating subpopulations of IgG-secreting hybridoma cells present at a frequency of approximately 1-10 in 10(6), we successfully isolated spontaneous and in vitro-induced isotypic switch variants in less than half the time required for conventional sublining. The effectiveness and specificity of the assay are demonstrated.

Cytokines and related receptor-mediated signaling pathways

Cytokines represent a multi-diverse family of polypeptide regulators; they are of relatively low molecular weight, pharmacologically active proteins that are secreted by one cell for the purpose of altering either its own functions (autocrine effect) or those of adjacent cells (paracrine effect). Cytokines are small, non-enzymatic glycoproteins whose actions are both diverse and overlapping (specificity/redundancy) and may affect diverse and overlapping target cell populations. In many instances, individual cytokines have multiple biological activities. Different cytokines can also have the same activity, which provides for functional redundancy within the inflammatory and immune systems. As biological cofactors that are released by specific cells, cytokines have specific effects on cell-cell interaction, communication, and behavior of other cells. As a result, it is infrequent that loss or neutralization of one cytokine will markedly interfere with either of these systems. The biological effect of one cytokine is often modified or augmented by another. Because an inter-digitating, redundant network of cytokines is involved in the production of most biological effects, both under physiologic and pathologic conditions, it usually requires more than a single defect in the network to alter drastically the outcome of the process. This fact therefore may have crucial significance in the development of therapeutic strategies for bio-pharmacologic intervention in cytokine-mediated inflammatory processes and infections.

Pharmaco-redox regulation of cytokine-related pathways: from receptor signaling to pharmacogenomics

Cytokines represent a multi-diverse family of polypeptide regulators; they are relatively low molecular weight (< 30 kDa), pharmacologically active proteins that are secreted by one cell for the purpose of altering either its own functions (autocrine effect) or those of adjacent cells (paracrine effect). Cytokines are small, nonenzymatic glycoproteins whose actions are both diverse and overlapping (specificity/redundancy) and may affect diverse and overlapping target cell populations. In many instances, individual cytokines have multiple biological activities. Different cytokines can also have the same activity, which provides for functional redundancy (network) within the inflammatory and immune systems. As biological cofactors that are released by specific cells, cytokines have specific effects on cell-cell interaction, communication, and behavior of other cells. As a result, it is infrequent that loss or neutralization of one cytokine will markedly interfere with either of these systems. The biological effect of one cytokine is often modified or augmented by another. Because an interdigitating, redundant network of cytokines is involved in the production of most biological effects, both under physiologic and pathologic conditions, it usually requires more than a single defect in the network to alter drastically the outcome of the process. This fact, therefore, may have crucial significance in the development of therapeutic strategies for biopharmacologic intervention in cytokine-mediated inflammatory processes and infections.

Modulation of human monocytes by Escherichia coli heat-labile enterotoxin B-subunit; altered cytokine production and its functional consequences

In murine systems, the B subunit of Escherichia coli heat-labile enterotoxin (EtxB) is a potent immunomodulator capable of suppressing Th1-mediated autoimmune diseases. This results from its ability to bind cell surface receptors, principally GM1-ganglioside, and as a consequence down-regulate the pathological T helper type 1 (Th1) response. The capacity of EtxB to alter human T-cell responses has not been investigated. Here we show that EtxB, but not the receptor non-binding mutant EtxB (G33D), triggers the release of interleukin (IL)-10, IL-6 and tumour necrosis factor-alpha (TNF-alpha) by human monocytes. The production of IL-8, transforming growth factor-beta (TGF-beta) or IL-12 was not enhanced by EtxB. Indeed, EtxB was shown to inhibit IL-12 secretion in monocytes stimulated with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) by an IL-10-independent mechanism. When EtxB-treated monocytes were used as antigen presenting cells in an allogeneic mixed lymphocyte reaction (MLR), IL-10 and IFN-gamma production were increased in comparison to levels seen in cultures stimulated with untreated monocytes; proliferation was unaltered. This modulation of the T-cell response was not only evident in the primary MLR triggered by EtxB-treated monocytes, but also upon restimulation of the responding T cells with fresh untreated monocytes; indicating that presentation by EtxB-treated monocytes leads to altered T-cell differentiation. Sorting experiments showed that IL-10 secreting T cells from the MLR cultures were strong suppressors of T-cell proliferation following their addition into a fresh primary MLR.

Controlling culture dynamics for the expansion of hematopoietic stem cells

The ex vivo expansion of hematopoietic stem cells (HSCs) is the subject of intense commercial and academic interest due to the potential of HSCs to be a renewable source of material for cellular therapeutics. Unfortunately, because methodologies have not yet been developed to grow clinically relevant numbers of HSCs (or their derivatives) consistently, the potential of this technology is limited. Manipulation of the in vitro culture microenvironment, primarily through cytokine supplementation, has been the predominant approach in studies attempting to expand primary human HSC numbers in vitro. While promising results have been obtained, it is becoming clear that novel methods must be developed before cellular therapies using these stem cells can become routine. Ideally, bioprocesses must be designed to target specifically the growth of stem cell populations while incorporating positive and negative feedback from potentially dynamic mature and maturing cell populations. The product of these culture systems should consist of not only HSCs, but also of cells that allow the engraftment of HSCs and, ideally, cells responsible for the immediate or accelerated functional support of patients. Development of such "designer transplants" will require combining optimal culture conditions capable of amplifying HSC numbers with novel approaches for finely controlling the number, functional capabilities, and characteristics of potentially therapeutic cells in these very complex cell culture systems.