Simultaneous quantitation of 15 cytokines using a multiplexed flow cytometric assay

Assessing Cellular Protein Phosphorylation: High Throughput Drug Discovery Technologies

Changes in protein phosphorylation mediate much of cellular physiology. Perturbations in the activity of the kinases that catalyze these reactions underlie numerous human pathologies, including metabolic and inflammatory disorders and most notably, cancer. HTS techniques that determine the activity of protein kinases in vitro are useful in the development of small molecule kinase inhibitors, but do not address underlying mechanistic concerns or efficient in vivo targeting. Observing protein phosphorylation in cell lysates and fixed cells in a high throughput manner is fundamental to understanding the mechanism of action of lead molecules and whether they target signaling pathways of interest. Herein we discuss several higher throughput techniques to study cellular protein kinase signal transduction and the strategies for implementation in kinase drug discovery.

DETECTION OF CRYPTOSPORIDIUM ANTIBODIES IN SERA AND ORAL FLUIDS USING MULTIPLEX BEAD ASSAY*

For the first time, a multiplex bead assay (MBA) was used to assay oral fluid and serum specimens for immunoglobulin G (IgG) antibodies to specific Cryptosporidium parvum antigens that were coupled to polystyrene beads. Recombinant C. parvum 17- and 27-kDa antigens (r17 and r27, respectively) both linked with glutathione-S-transferase (GST) fusion proteins, native 17-kDa antigen, and GST alone were each coupled to microspheres that could be differentiated based on variable amounts of internally incorporated red fluorescent dye. Initial and follow-up serum and oral fluid specimens from a 1997 cryptosporidiosis outbreak in Spokane, Washington, were incubated with the coupled beads. Antibodies bound to the coupled beads were detected using biotinylated monoclonal anti-human IgG antibody and streptavidin-labeled r-phycoerythrin. Fluorescence intensity was measured by flow cytometry. For the 3 C. parvum antigens, the median of the mean fluorescence intensity (MFI) was significantly higher (P < 0.03) in the initial specimens than in the follow-up specimens. No significant change in IgG responses to GST in oral fluids or serum specimens was observed. For all Cryptosporidium antigens, the MFI in the initial serum specimens correlated with the MFI in the initial oral fluid specimens (P < 0.001, r > 0.673). For the recombinant antigens used in the MBA, the MFI correlated with the response as measured by an enzyme-linked immunosorbent assay that used r17 and r27 expressed without the GST fusion partner (P < 0.001, r > 0.854). MBA using sera or more conveniently collected oral fluids, especially from children, may be an option for immunodiagnosis of C. parvum infection and for prospective epidemiological studies designed to monitor infection risk.

CD40-induced aggregation of MHC class II and CD80 on the cell surface leads to an early enhancement in antigen presentation

Ligation of CD40 on B cells increases their ability to present Ag and to activate MHC class II (MHC-II)-restricted T cells. How this occurs is not entirely clear. In this study we demonstrate that CD40 ligation on Ag-presenting B cells (APC) for a short period between 30 min and 3 h has a rapid, augmenting effect on the ability of a B cell line and normal B cells to activate T cells. This is not due to alterations in Ag processing or to an increase in surface expression of CD80, CD86, ICAM-1, or MHC-II. This effect is particularly evident with naive, resting T lymphocytes and appears to be more pronounced under limiting Ag concentrations. Shortly after CD40 ligation on a B cell line, MHC-II and CD80 progressively accumulated in cholesterol-enriched microdomains on the cell surface, which correlated with an initial enhancement in their Ag presentation ability. Moreover, CD40 ligation induced a second, late, more sustained enhancement of Ag presentation, which correlates with a significant increase in CD80 expression by APC. Thus, CD40 signaling enhances the efficiency with which APC activate T cells by at least two related, but distinct, mechanisms: an early stage characterized by aggregation of MHC-II and CD80 clusters, and a late stage in which a significant increase in CD80 expression is observed. These results raise the possibility that one important role of CD40 is to contribute to the formation of the immunological synapse on the APC side.

Architectural Changes in the TCR:CD3 Complex Induced by MHC:Peptide Ligation

A hallmark of T cell activation is the ligation-induced down-modulation of the TCR:CD3 complex. However, little is known about the molecular events that drive this process. The CD3 zeta-chain has been shown to play a unique role in regulating the assembly, transport, and cell surface expression of the TCR:CD3 complex. In this study we have investigated the relationship between CD3zeta and the TCRalphabetaCD3epsilondeltagamma complex after ligation by MHC:peptide complexes. Our results show that there is a significant increase in free surface CD3zeta, which is not associated with the TCR:CD3 complex, after T cell stimulation. This may reflect dissociation of CD3zeta from the TCRalphabetaCD3epsilondeltagamma complex or transport of intracellular CD3zeta directly to the cell surface. We also show that MHC:peptide ligation also results in exposure of the TCR-associated CD3zeta NH2 terminus, which is ordinarily buried in the complex. These observations appears to be dependent on Src family protein tyrosine kinases, which are known to be critical for efficient T cell activation. These data suggest a mechanism by which ligated TCR may be differentiated from unligated TCR and selectively down-modulated.

Cytometric bead array: a multiplexed assay platform with applications in various areas of biology

The introduction of flow cytometric bead-based technology has added a new approach for investigators to simultaneously measure multiple analytes in biological and environmental samples. This new technology allows for (1) evaluation of multiple analytes in a single sample; (2) utilization of minimal sample volumes to glean data; (3) reproducibility and results comparative with previous experiments; (4) direct comparison with existing assays; and (5) a more rapid evaluation of multiple samples in a single platform. The cytometric bead array (CBA) system enables simultaneous measurement of multiple analytes in sample volumes too small for traditional immunoassays. Results have been presented for the analysis of a variety of human cytokines. In addition, the technology allows for the design and creation of assays to measure a variety of analytes including inflammatory mediators, chemokines, immunoglobulin isotypes, intracellular signaling molecules, apoptotic mediators, adhesion molecules, and antibodies. New initiatives put forward by the Human Genome Project and the FDA require the development and use of assays for the rapid simultaneous quantitation of multiple analytes. The CBA technology provides the ability to quantify multiple proteins within a given sample, with precision and consistency.

Allergen-loaded biodegradable poly(d,l-lactic-co-glycolic) acid nanoparticles down-regulate an ongoing Th2 response in the BALB/c mouse model

BACKGROUND AND OBJECTIVE

Biocompatible and biodegradable microparticles have gained interest as antigen delivery systems during the recent years. We investigated whether biodegradable poly(d,l-lactic-co-glycolic) acid (PLGA) nanospheres could be used as allergen vehicles for few-shot therapy of type I allergy.

METHODS

The major birch pollen allergen Bet v 1 was encapsulated in PLGA nanospheres (PLGA-Bet v 1). We examined the antigenicity and the immune response to PLGA-Bet v 1 in a BALB/c mouse model.

RESULTS

The antigenicity of Bet v 1 was largely unaffected by PLGA entrapment. When BALB/c mice were immunized subcutaneously with PLGA-Bet v 1, they formed allergen-specific IgG antibodies, but did not develop hypersensitivity to Bet v 1, as shown by type I skin tests. To evaluate their therapeutic potential, PLGA-Bet v 1 with or without Al(OH)3 or non-entrapped Bet v 1 with Al(OH)3 were used for single-shot treatment of sensitized mice. Both groups treated with PLGA-Bet v 1 developed high levels of Bet v 1-specific IgG2a antibodies (P<0.01), whereas IgG1 levels decreased significantly (P<0.01). Moreover, T cells from mice treated with PLGA-Bet v 1 showed IFN-gamma and IL-10 production. The synthesis of these cytokines was enhanced in the groups where Al(OH)3 had been added to the vaccine formulation.

CONCLUSION

Allergen-loaded PLGA nanoparticles modulate an ongoing Th2 response in the BALB/c mouse model, as demonstrated by down-regulation of IgG1 and production of IFN-gamma and IL-10. Our data strongly suggest that PLGA nanospheres can advantageously be used for formulations of allergen extracts or allergen derivatives for the few-shot treatment of type I allergy.

Developments in diagnostic techniques for differentiating infection from vaccination in foot-and-mouth disease

Foot-and-mouth disease (FMD) is a highly contagious and economically significant disease of cattle, pigs, sheep, goats and wild ruminant species. The FMD virus genome encodes a unique polyprotein from which the different viral polypeptides are cleaved by viral proteases, including eight different non-structural proteins (NSPs). Both structural and non-structural antigens induce the production of antibodies in infected animals. In contrast, vaccinated animals which have not been exposed to replicating virus will develop antibodies only to the viral antigens in the inactivated material. Vaccination against FMD is a key element in the control of the disease in addition to slaughter and movement restrictions. However, countries that vaccinate in the event of an outbreak will have to re-establish their FMD free status to the satisfaction of their trading partners. Because currently available vaccines stimulate the production of antibodies indistinguishable from those produced by infected animals in response to live virus and because vaccinated animals can be infected and become carriers of FMD virus, efforts have been made to develop diagnostic test that can differentiate vaccinated animals from those that are convalescent and from those that have been vaccinated and become carriers following subsequent contact with live virus. Currently the detection of antibodies to non-structural protein's (NSPs) is the preferred diagnostic method to distinguish virus infected, carrier, animals from vaccinated animals. However this is currently only possible at the herd level because of the great variability in the initiation, specificity and duration of the immune response in individual animals to the NSPs shown in many studies. Considerable effort and attention is now being directed toward the development of new methods and techniques for the rapid and accurate detection of anti-NSP antibodies, harmonization and standardization of current diagnostic techniques, as well as the production of defined reagents.

Microsphere-based duplexed immunoassay for influenza virus typing by flow cytometry

We have developed a rapid, duplexed microsphere-based immunoassay for the characterization of influenza virus types that has the potential to overcome many of the limitations of current detection methods. The assay uses microspheres of two sizes, each coupled to an influenza type A- or type B-specific monoclonal antibody (MAb), to capture influenza viruses in the sample. A cocktail of fluorescently labeled, influenza-specific polyclonal antibodies then binds the captured viruses. The sandwich complexes are measured using a multiparameter flow cytometer. The assay can distinguish between influenza types A and B in a single reaction with good reproducibility and high sensitivity. Detection sensitivity is much higher than that of commercially available influenza diagnosis quick kits: the FLU OIA (Thermo Biostar) kit and the Directigen Flu A+B kit (Becton Dickinson). The multiplexing capabilities of the current assay, which are not possible with enzyme-linked immunosorbent assay (ELISA) and the commercially available kits, reduce sample handling and consume fewer costly reagents. This assay represents a more efficient and sensitive method of characterizing influenza types. With inclusion of influenza subtype-specific antibodies as capture antibodies, this microsphere-based immunoassay can be expanded to differentiate among influenza types and subtypes in a single reaction to improve world-wide influenza surveillance.

Automated Microarray System for the Simultaneous Detection of Antibiotics in Milk

A parallel affinity sensor array (PASA) for the rapid automated analysis of 10 antibiotics in milk is presented, using multianalyte immunoassays with an indirect competitive ELISA format. Microscope glass slides modified with (3-glycidyloxypropyl)trimethoxysilane were used for the preparation of hapten microarrays. Protein conjugates of the haptens were immobilized as spots on disposable chips, which were processed in a flow cell. Monoclonal antibodies against penicillin G, cloxacillin, cephapirin, sulfadiazine, sulfamethazine, streptomycin, gentamicin, neomycin, erythromycin, and tylosin allowed the simultaneous detection of the respective analytes. Antibody binding was detected by a second antibody labeled with horseradish peroxidase generating enhanced chemiluminescence, which was recorded with a sensitive CCD camera. All liquid handling and sample processing was fully automated, and one analysis was carried out in milk within less than 5 min. The detection limits ranged from 0.12 (cephapirin) to 32 microg/L (neomycin). Penicillin G could be detected at the maximum residue limit (MRL); the detection limits for all other analytes were far below the respective MRLs. The PASA system proved to be the first immunochemical biosensor platform having the potential to test for numerous antibiotics in parallel, such being of considerable interest for the control of milk in the dairy industry.

The urokinase receptor (uPAR, CD87) as a target for tumor therapy: uPA-silica particles (SP-uPA) as a new tool for assessing synthetic peptides to interfere with uPA/uPA-receptor interaction

Many different processes in the physiology and pathophysiology of human beings are regulated protein/protein interactions such as receptor/ligand interactions. A more detailed knowledge of the nature of receptor/ligand binding sites and mechanisms of interaction is necessary as well in order to understand the process of cancer spread and metastasis. For instance, the cell surface receptor uPAR (CD87) and its ligand, the serine protease urokinase-type plasminogen activator (uPA), facilitate tumor invasion and metastasis in solid malignant tumors. Besides its proteolytic function in activating the zymogen plasminogen into the serine protease plasmin, binding of uPA to tumor cell-associated uPAR initiates various cell responses such as tumor cell migration, adhesion, proliferation, and differentiation. Hence, the tumor-associated uPA/uPAR system is considered a potential target for cancer therapy. Here we briefly describe a new technology using micro-silica particles coated with uPA (yields SP-uPA) and reaction of SP-uPA with recombinant soluble uPAR (suPAR) to test the competitive antagonistic potential of synthetic uPA peptides by flow cytofluorometry (FACS). We discuss the data obtained with the SP-uPA system from two different points of view: (1) The enhanced potential of improved uPA-derived synthetic peptides compared to previously described peptides, and (2) comparison of the new technique to other test systems currently used to identify uPA/uPAR or other protein/protein interactions.

Comparison of intracellular cytokine production with extracellular cytokine levels using two flow cytometric techniques

BACKGROUND

We investigated the relation between intracellular cytokine production and extracellular cytokine levels by using two flow cytometric techniques.

METHODS

A two-color flow cytometric technique was used to measure interleukin (IL)-1beta, IL-6, tumor necrosis factor alpha (TNF-alpha), IL-10, and IL-12 production blocked intracellularly with brefeldin A in lipopolysaccharide (LPS)-stimulated CD14(+) monocytes and IL-2, IL-4, and IFN-gamma production in phorbol-12-mirystate-13-acetate (PMA)-stimulated CD3(+) T lymphocytes in samples from patients with rheumatoid arthritis. A flow cytometric microsphere-based immunoassay was performed to detect cytokine secretion in plasma of PMA- and LPS-stimulated whole blood samples.

RESULTS

There was a strong linear correlation between extracellular quantitative (pg/ml) and intracellular semiquantitative detection of LPS-stimulated IL-1beta, IL-6, IL-10, and IL-12 production (r > 0.9). For lymphocytes, extracellularly detected IL-2 and IFN-gamma correlated well with percentages of cytokine-producing cells (r > 0.8). The percentages of IL-4-positive T cells were moderately correlated with the secreted amounts of IL-4 as detected with the microsphere-based immunoassay (r = 0.7).

CONCLUSION

Overall, there was a good correlation between semiquantitative intracellular detection of cytokines and the secreted amounts of cytokines detected with the microsphere based immunoassay.

Multiplexed microsphere-based flow cytometric immunoassays for human cytokines

Cytokines play a pivotal role in the regulation of immunologic, hematologic and wound-healing processes. They function to stimulate as well as inhibit the proliferation, differentiation and maturation of a variety of cell types. Thus, their functions are pleiotropic as well as interdependent to the extent that any cytokine may have effects that are synergistic or antagonistic with other cytokines. Cytokines also display redundancy when one mimics the functions of others. These characteristics imply that measuring the levels of one cytokine in a biologic system provides only a fraction of the information that is relevant to the existing physiologic state. A more realistic indication of the complexity of cellular interactions would include measurements of multiple cytokines at any time point. One method of multiplexed analysis can be performed by capture of the cytokines on an array of fluorescent microspheres for quantitation by flow cytometry. This technology has been applied to a variety of biomolecules, but simultaneous quantitation of multiple cytokines in a small sample volume has become rapid, inexpensive, reliable and informative.

Dielectrically Addressable Microspheres Engineered Using Self-Assembled Monolayers

We have used self-assembled monolayer techniques to produce a new class of microspheres with specifically engineered dielectric properties to enable their dielectrophoretic manipulation and identification in microsystems. Dielectrophoresis is an electrokinetic phenomenon that exploits frequency-dependent polarizability differences between a particle and its suspending medium to drive the movement of the particle toward or away from the high-field regions of an inhomogeneous electric field. While dielectrophoretic methods have been used extensively for cell manipulation, separation, and identification, we wished to extend the applicability of dielectrophoresis to molecular analysis by developing a panel of dielectric microspheres or "handles". Dielectric shell theory was used to model the dielectrophoretic response for a biomimetic particle composed of a thin insulating shell over a conductive interior. We specifically sought to modulate the specific capacitance, and thereby the dielectric properties, of the particle by controlling the thickness of the insulating layer. Such a structure was fabricated by covering a gold-coated polystyrene core particle with self-assembled monolayers of alkanethiol and phospholipid. To test the prediction that the carbon chain length of these layers should dictate the dielectric properties of the particles, we constructed a panel of six microsphere types with shell compositions ranging from a C(9) alkanethiol monolayer to a C(32) hybrid bilayer membrane. These microsphere populations were distinguishable and manipulatable by dielectrophoresis in a characteristic, frequency-dependent manner as predicted by theory. Experimentally derived specific membrane capacitance values were inversely related to the insulating shell thickness and agreed with published capacitance values for planar layers of similar thicknesses. These proof of principle studies are the first to demonstrate that the dielectric properties of particles can be specifically engineered to allow their dielectrophoretic manipulation and are a first step toward the development of bead-based dielectrophoretic microsystems for multiplexed molecular separation and analysis.

Simultaneous detection of 15 human cytokines in a single sample of stimulated peripheral blood mononuclear cells

Cytokines secreted by cells of the immune system can alter the behavior and properties of immune or other cells. At a site of inflammation, sets of cytokines interact with immune cells, and their combined effect is often more important than the function of one isolated component. Conventional techniques, such as enzyme-linked immunosorbent assays, generally require large quantities of cells to characterize a complete cytokine profile of activated lymphocytes. The Bio-Plex system from Bio-Rad Laboratories combines the principle of a sandwich immunoassay with the Luminex fluorescent-bead-based technology. We developed a multiplex cytokine assay to detect different cytokines simultaneously in culture supernatant of human peripheral blood mononuclear cells stimulated with antigen and with mitogen. Fifteen human cytokines (interleukin 1alpha [IL-1alpha], IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-13, IL-15, IL-17, IL-18, gamma interferon, and tumor necrosis factor alpha) were validated with a panel of healthy individuals, rheumatoid arthritis patients, and juvenile idiopathic arthritis patients. Comparing the multiplex assay with a regular enzyme-linked immunosorbent assay technique with this donor panel resulted in correlation coefficients for all cytokines ranging from 0.75 to 0.99. Intra-assay variance proved to be less then 10%, whereas interassay variability ranged between 10 and 22%. This multiplex system proved to be a powerful tool in the quantitation of cytokines. It will provide a more complete picture in differences between activated lymphocyte cytokine profiles from healthy individuals and those from patients with chronic inflammatory diseases.

Multiplexed microsphere-based flow cytometric assays

Flow cytometry has become an indispensable tool for clinical diagnostics and basic research. Although primarily designed for cellular analysis, flow cytometers can detect any particles in the lower micron range, including inert microspheres of different sizes, dyed with various fluorochromes. Over the past 20 years, microspheres have been used as calibrators for flow cytometers and also as a solid support for numerous molecular reactions quantitated by flow cytometry. Proteins, oligonucleotides, polysaccharides, lipids, or small peptides have been adsorbed or chemically coupled to the surface of microspheres to capture analytes that are subsequently measured by a fluorochrome-conjugated detection molecule. More recently, assays for similar analytes have been multiplexed, or analyzed in the same assay volume, by performing each reaction on a set of microspheres that are dyed to different fluorescent intensities and, therefore, are spectrally distinct. Some recent applications with fluorescent microspheres have included cytokine quantitation, single nucleotide polymorphism genotyping, phosphorylated protein detection, and characterization of the molecular interactions of nuclear receptors. The speed, sensitivity, and accuracy of flow cytometric detection of multiple binding events measured in the same small volume have the potential to replace many clinical diagnostic and research methods and deliver data on hundreds of analytes simultaneously.

Array-based multiplexed screening and quantitation of human cytokines and chemokines

HydroGel-coated slide is a porous substrate based on a polymer matrix that provides a three-dimensional hydrophilic environment similar to free solution suitable for biomolecular interactions. This substrate has been used to develop fluorescence-based multiplexed cytokine immunoassays. Forty-three monoclonal antibodies (mAb) of cytokines and chemokines were printed at a volume of 350 pL per spot using a Packard BioChip Arrayer. For each probe, four replicates were printed at a pitch of 500 microm in the layout of a 13 x 16 pattern on a 12 x 12 mm2 HydroGel pad. Cytokines and chemokines that are captured by the arrayed mAbs are detected by using another biotinylated mAb, following by the addition of a Texas Red-conjugated streptavidin. The fluorescent images of arrays were recorded using a Packard ScanArray 5000 confocal slide scanner and quantitated using Packard QuantArray software. Experiments demonstrated that 43 cytokines and chemokines could be simultaneously screened and quantitated in conditioned culture media, cell lysates, and human plasma. Using this chip, we have examined cytokine expression in breast cancer cells and identified the chemokines associated with human cervical cancers.

Encoding microcarriers: present and future technologies

In answer to the ever-increasing need to carry out many assays simultaneously in drug screening and drug discovery, several microcarrier-based multiplex technologies have arisen in the past few years. The compounds to be screened are attached to the surface of microcarriers, which can be mixed together in a vessel that contains the target analyte. Each microcarrier has to be encoded to know which compound is attached to its surface. In this article, the methods that have been developed for the encoding of microcarriers are reviewed and discussed.

A comparison of ELISA and flow microsphere-based assays for quantification of immunoglobulins

An automated microsphere-based flow cytometric assay (FlowMetrix system) was compared with a conventional enzyme-linked immunosorbent assay (ELISA) for quantifying Ig classes in serum and stool samples. The reproducibility of the process of coupling capture antibodies to microspheres was tested. The use of independently coupled microspheres did not increase the variation of assay results relative to using the same bead set in repeated assays. However, it is necessary to ensure quality control of the coupling process since slight variations in the coupling procedures can profoundly affect the density of capture reagents coupled to the microspheres and consequently adversely affect assay precision. Although the ELISA was more sensitive and did not have the problems with instrument performance encountered with the FlowMetrix assay, the latter was more reproducible, had a greater dynamic range of measurement, and took considerably less preparation time than the ELISA. Greater reproducibility is especially important for measurement of fecal Ig, which is typically highly variable. Thus, in addition to its multi-analyte capability, the FlowMetrix assay system has definite advantages over a conventional ELISA. Mechanical problems such as microspheres settling to the bottom of wells during analysis by an automated plate reader will likely be overcome, and sensitivity improved as this technology develops.

Multiplexed immunoassays by flow cytometry for diagnosis and surveillance of infectious diseases in resource-poor settings

An accurate, rapid and cost-effective diagnosis is the cornerstone of efficient clinical and epidemiological management of infections. Here we discuss the relevance of an emerging technology, multiplexed immunoassays read by flow cytometry, for the diagnosis of infectious diseases. In these assays, multiple fluorescent microspheres, conjugated to different antigens or antibodies, constitute the solid phase for detecting antibodies or antigens in biological samples. These assays seem to be more sensitive than traditional immunoassays, have a high throughput capacity, and provide a wide analytical dynamic range. Additionally, they have multiplexing ability-ie, they are capable of measuring multiple antibodies or antigens simultaneously. We discuss four different areas where this technology could make an impact in resource-poor settings: (i) infections causing rash and fever in children; (ii) sero-epidemiological studies on vaccine-preventable diseases; (iii) management of genital ulcers and vaginal discharge; and (iv) screening of infections in blood banking. We predict a widespread use for a new breed of small, affordable, practical flow cytometers as field instruments for replacing ELISA and RIA tests, which will also be capable of doing cellular immunological tests such as CD4+ T-cell enumeration and Plasmodium falciparum detection in whole blood.

Emerging technology and future developments in flow cytometry

The authors' view of the future of flow cytometry is based on a belief that the single most important aspect flow cytometry offers to the investigator is high-speed interrogation of correlated measurements on a cell-by-cell basis. Over the next several years, an enormous increase in the capabilities of cytometry in general, and flow cytometry in particular, is likely to occur. A brief description of some of those capabilities is the subject of this article.

Simultaneous analysis of eight human Th1/Th2 cytokines using microarrays

The adaptive immune system induces T cells to change from a naive phenotype to a Th1/Th2 phenotype each of which produce characteristic types of cytokines. Knowledge of whether a specific immune response is Th1 or Th2 is a useful indicator for diseases with basis in immune function disorder. An assay that can rapidly analyze multiple cytokines indicative of these two cell types from small sample quantities can be an extremely useful research and diagnostic tool. Silanized glass slides were printed with multiple arrays of capture antibodies to detect eight different cytokines involved in the Th1/Th2 response along with control proteins for assessing assay performance. Arrays were developed by sequential addition of known antigen amounts, detector antibodies and a fluorescent detection system followed by imaging and quantification. These arrays were used to determine the specificity, sensitivity and reproducibility of the assay and the performance compared with conventional ELISA. This multiplexed assay is able to measure human Th1/Th2 cytokines in sample volumes lower than 20 microl. The assay sensitivity for the eight cytokines range from 0.3 microg/l for IL-4 to 6.4 microg/l for IL-5 which are either comparable to or higher than those reported for conventional ELISA or bead-based multiplex ELISA methods. This assay can be automated to measure expression levels of multiple Th1/Th2 cytokines simultaneously from tens to hundreds of biological samples. This assay platform is more sensitive and has a larger dynamic range as compared to a conventional ELISA in addition to significantly reducing the time and cost of assay. This platform provides a versatile system to rapidly quantify a wide variety of proteins in a multiplex format.

Miniaturised multiplexed immunoassays

Miniaturised immunoassays are of general interest for applications that require the simultaneous determination of different parameters from a minute sample of material. Apart from planar microarray-based systems, bead-based flow cytometric approaches are well suited for the multiplexed detection of target molecules, especially when the number of parameters that have to be determined in parallel is limited.

Simultaneous quantification of proinflammatory cytokines in human plasma using the LabMAP assay

There is an emerging trend in the pharmaceutical industry to evaluate a variety of surrogate biomarkers in Phase I/II clinical studies with the intention of determining potential activity of drugs early in clinical development. A number of cytokines expressed in pathological conditions are currently being considered as potential surrogates of disease and/or drug activity. The quantitative measurement of such analytes (biomarkers) in biological fluids has traditionally been performed by bioassays, enzyme-linked immunosorbent assay (ELISA), ribonuclease protection assay (RPA) and polymerase chain reaction (PCR). Typically, these methods have been limited to the measurement of a single analyte, require large sample volume and are time and cost involved. The LabMAP (Luminex) system has been previously used to quantify cytokines in tissue culture supernatants and in animal serum. In the present study, the LabMAP technology was used for quantifying for the first time, pro-inflammatory cytokines such as, tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1beta), IL-6 and IL-8 levels in lipopolysaccharide (LPS)-stimulated human plasma samples. Both single-cytokine and two-cytokine (biplexed) panel formats were evaluated and the performance in the two formats was compared. A detailed validation procedure for these determinations is described along with a side-by-side comparison with ELISA results. Our results indicate that the LabMAP system can be used to measure cytokine levels in LPS-stimulated human plasma samples and that the levels obtained by this technique are comparable with ELISA results. It is therefore feasible to use this optimized technology to detect and quantify cytokines and other potential biomarkers in a complex milieu such as human plasma in support of clinical studies.

Suspension array technology: evolution of the flat-array paradigm

Suspension arrays of microspheres analyzed using flow cytometry offer a new approach to multiplexed assays for large-scale screening applications. By optically encoding micron-sized polymer particles, suspension microarrays can be created to enable highly multiplexed analysis of complex samples. Each element in the array is comprised of a subpopulation of particles with distinct optical properties and each array element bears a different surface receptor. Nucleic acids, proteins, lipids or carbohydrates can serve as receptors to support the analysis of a wide range of biomolecular assemblies, and applications in genomic and proteomic research are being developed. Coupled with recent innovations for rapid serial analysis of samples, molecular analysis with microsphere arrays holds significant potential as a general analysis platform for both research and clinical applications.

uPA-silica-Particles (SP-uPA): a novel analytical system to investigate uPA-uPAR interaction and to test synthetic uPAR antagonists as potential cancer therapeutics

The urokinase-type plasminogen activation system, including the serine protease uPA (urokinase-type plasminogen activator) and its cell surface receptor (uPAR, CD87), are important key molecules in tumor invasion and metastasis. Besides its proteolytic function, binding of uPA to uPAR on tumor cells exerts various cell responses such as migration, adhesion, proliferation, and differentiation. Hence, the uPA/uPAR system is a potential target for tumor therapy. We have designed a new generation of uPA-derived synthetic cyclic peptides suited to interfere with the binding of uPA to uPAR and present a new technology involving micro silica particles coated with uPA (SP-uPA) and reacting with recombinant soluble uPAR (suPAR), to rapidly assess the antagonistic potential of uPA-peptides by flow cytofluorometry (FACS). For this, we used silica particles of 10 microm in diameter to which HMW-uPA is coupled using the EDC/NHS method. Soluble, recombinant suPAR was added and the interaction of SP-uPA with suPAR verified by reaction with monoclonal antibody HD13.1 directed to uPAR, followed by a cyan dye (cy5)-labeled antibody directed against mouse IgG. Thereby it was possible to test naturally occurring ligands of uPAR (HMW-uPA, ATF) as well as highly effective, synthetic cyclic uPA-derived peptides (cyclo21,29[D-Cys21Cys29]-UPA21-30, cyclo21,29[D-Cys21Nle28Cys29]-uPA21-30, cyclo21,29[D-Cys(21)2-Nal24Cys29]-uPA21-30, and cyclo21,29[D-Cys21Orn23Thi24Thi25Cys29]-uPA21-30. The results obtained with the noncellular SP-uPA/uPAR system are highly comparable to those obtained with a cellular system involving FITC-uPA and the promyeloid cell line U937 as the source of uPAR.

Silicon-based Biosensors for Rapid Detection of Protein or Nucleic Acid Targets

Background: We developed a silicon-based biosensor that generates visual, qualitative results or quantitative results for the detection of protein or nucleic acid targets in a multiplex format.

Methods: Capture probes were immobilized either passively or covalently on the optically coated surface of the biosensor. Intermolecular interactions of the immobilized capture probe with specific target molecules were transduced into a molecular thin film. Thin films were generated by enzyme-catalyzed deposition in the vicinity of the surface-bound target. The increased thickness on the surface changed the apparent color of the biosensor by altering the interference pattern of reflected light.

Results: Cytokine detection was achieved in a 40-min multiplex assay. Detection limits were 4 ng/L for interleukin (IL)-6, 31 ng/L for IL1-β, and 437 ng/L for interferon-γ. In multianalyte experiments, cytokines were specifically detected with signal-to-noise ratios ranging from 15 to 80. With a modified optical surface, specificity was also demonstrated in a nucleic acid array with unambiguous discrimination of single-base changes in a 15-min assay. For homozygous wild-type and homozygous mutant samples, signal-to-noise ratios of ∼100 were observed. Heterozygous samples yielded approximately equivalent signals for wild-type and mutant capture probes.

Conclusions: The thin-film biosensor allows rapid, sensitive, and specific detection of protein or nucleic acid targets in an array format with results read visually or quantified with a charge-coupled device camera. This biosensor is suited for multianalyte detection in clinical diagnostic assays.

Human NKT cells mediate antitumor cytotoxicity directly by recognizing target cell CD1d with bound ligand or indirectly by producing IL-2 to activate NK cells

alpha-Galactosylceramide (alphaGalCer) stimulates NKT cells and has antitumor activity in mice. Murine NKT cells may directly kill tumor cells and induce NK cell cytotoxicity, but the mechanisms are not well defined. Newly developed human CD1d/alphaGalCer tetrameric complexes were used to obtain highly purified human alphaGalCer-reactive NKT cell lines (>99%), and the mechanisms of NKT cell cytotoxicity and activation of NK cells were investigated. Human NKT cells were cytotoxic against CD1d(-) neuroblastoma cells only when they were rendered CD1d(+) by transfection and pulsed with alphaGalCer. Four other CD1d(-) tumor cell lines of diverse origin were resistant to NKT cells, whereas Jurkat and U937 leukemia cell lines, which are constitutively CD1d(+), were killed. Killing of the latter was greatly augmented in the presence of alphaGalCer. Upon human CD1d/alphaGalCer recognition, NKT cells induced potent cytotoxicity of NK cells against CD1d(-) neuroblastoma cell lines that were not killed directly by NKT cells. NK cell activation depended upon NKT cell production of IL-2, and was enhanced by secretion of IFN-gamma. These data demonstrate that cytotoxicity of human NKT cells can be CD1d and ligand dependent, and that TCR-stimulated NKT cells produce IL-2 that is required to induce NK cell cytotoxicity. Thus, NKT cells can mediate potent antitumor activity both directly by targeting CD1d and indirectly by activating NK cells.

Multiplexed fluorescent bead-based immunoassays for quantitation of human cytokines in serum and culture supernatants

BACKGROUND

An increasing volume of data suggests a relationship between cytokine levels in human body fluids and disease pathogenesis. Traditionally, many individual assays would be performed to measure the large number of known cytokines and determine their associations with disease. A new technique for the simultaneous measurement of multiple cytokines in cell culture supernatants by fluorescent microsphere-based flow cytometry was adapted to human sera.

METHODS

Multiplexed sandwich immunoassays for eight cytokines were developed by coupling cytokine-specific capture antibodies to beads with different emission spectra. The binding of biotinylated detection antibodies bound with a streptavidin-conjugated fluorochrome was analyzed. Recovery of "spiked" cytokines, sensitivity, and variability of the assays were evaluated. In addition, the results of the bead assays were compared with the results of commercial enzyme-linked immunosorbent assays (ELISAs) that used the same antibody pairs.

RESULTS

Correlations of the bead assays and the ELISAs were 0.974 (n = 18) for supernatant samples and 0.859 (n = 28) for serum samples. High, false-positive values observed with some sera, assumed to be produced by heterophilic antibodies, were reduced by preincubation with a cocktail of animal sera.

CONCLUSIONS

Fluorescent bead-based immunoassays can be used to quantitate multiple cytokines in human sera and contribute to an understanding of the role of cytokines in disease processes. This methodology is applicable to many combinations of purified analytes and high-affinity antibodies. Published 2001 Wiley-Liss, Inc.

Multiplexed molecular interactions of nuclear receptors using fluorescent microspheres

BACKGROUND

We describe a novel microsphere-based system to identify and characterize multiplexed interactions of nuclear receptors with peptides that represent the LXXLL binding region of coactivator proteins.

METHODS

In this system, individual microsphere populations with unique red and orange fluorescent profiles are coupled to specific coactivator peptides. The coactivator peptide-coupled microsphere populations are combined and incubated with a nuclear receptor that has been coupled to a green fluorochrome. Flow cytometric analysis of the microspheres simultaneously decodes each population and detects the binding of receptor to respective coactivator peptides by the acquisition of green fluorescence.

RESULTS

We have used this system to determine the binding affinities of human estrogen receptor beta ligand binding domain (ERbeta LBD) and human peroxisome proliferator activated receptor gamma ligand binding domain (PPARgamma LBD) to a set of 34 coactivator peptides. Binding of ERbeta LBD to a coactivator peptide sequence containing the second LXXLL motif of steroid receptor coactivator-1 (SRC-1(2) (676-700) is shown to be specific and saturable. Analysis of receptor binding to a multiplexed set of coactivator peptides shows PPARgamma LBD binds with high affinity to cAMP response element binding protein (CBP) peptides and to the related P300 peptide while ERbeta LBD exibits little binding to these peptides. Using the microsphere-based assay we demonstrate that ERbeta LBD and PPARgamma LBD binding affinities for the coactivator peptides are increased in the presence of agonist (estradiol or GW1929, respectively) and that ERbeta LBD binding is decreased in the presence of antagonist (raloxifene or tamoxifen).

CONCLUSIONS

This unique microsphere-based system is a sensitive and efficient method to simultaneously evaluate many receptor-coactivator interactions in a single assay volume. In addition, the system offers a powerful approach to study small molecule modulation of nuclear receptor binding.

Flow cytometric microsphere-based immunoassay: analysis of secreted cytokines in whole-blood samples from asthmatics

The ability of flow cytometry to resolve multiple parameters was used in a microsphere-based flow cytometric assay for the simultaneous determination of several cytokines in a sample. The flow cytometer microsphere-based assay (FMBA) for cytokines consists of reagents and dedicated software, specifically designed for the quantitative determination of cytokines. We have made several improvements in the multiplex assay: (i) dedicated software specific for the quantitative multiplex assay that processes data automatically, (ii) a stored master calibration curve with a two-point recalibration to adjust the stored curve periodically, and (iii) an internal standard to normalize the detection step in each sample. Overall analytical performance, including sensitivity, reproducibility, and dynamic range, was investigated for interleukin-4 (IL-4), IL-6, IL-10, IL-12, gamma interferon (IFN-gamma), and tumor necrosis factor alpha. These assays were found to be reproducible and accurate, with a sensitivity in the picograms-per-milliliter range. Results obtained with FMBA correlate well with commercial enzyme-linked immunosorbent assay data (r > 0.98) for all cytokines assayed. This multiplex assay was applied to the determination of cytokine profiles in whole blood from atopic and nonatopic patients. Our results show that atopic subjects' blood produces more IL-4 (P = 0.003) and less IFN-gamma (P = 0.04) than the blood of nonatopic subjects. However, atopic asthmatic subjects' blood produces significantly more IFN-gamma than that of atopic nonasthmatic subjects (P = 0.03). The results obtained indicate that the FMBA technology constitutes a powerful system for the quantitative, simultaneous determination of secreted cytokines in immune diseases.

Cell function-based flow cytometry

Flow cytometry is increasingly used to assess the functional status of leukocytes, and practically all aspects of their life (and death) are accessible to flow cytometric study. Together with familiar features of flow cytometry, such as multiparameter immunophenotyping, cell function-based flow cytometry has provided many new insights into the relationships among lymphocyte cell surface features; intracellular processes, such as cytokine production and protein phosphorylation; and the functional status of lymphocytes in a variety of human diseases. Direct visualization and quantification of antigen-specific T cells using major histocompatibility complex (MHC)-peptide tetramer technology, in combination with functional assays, has provided the means to study specific T-cell subsets of interest. Even early in its development, this technology already has offered a better understanding of basic and clinical immunology and has invited reassessment of several long-standing immunologic concepts. Semin Hematol 38:169-178. This is a US government work. There are no restrictions on its use.

Comprehensive gene expression profile of human activated T(h)1- and T(h)2-polarized cells

In response to antigen stimulation, T(h) cells differentiate into two types of effector cells, T(h)1 and T(h)2. T(h)1 cells predominantly mediate cellular immunity, whereas T(h)2 cells induce humoral allergic responses. We have conducted here serial analysis of gene expression (SAGE) in human activated T(h)1- and T(h)2-polarized cells from cord blood. SAGE analysis of 64,510 tags (32,219 and 32,291 tags from T(h)1 and T(h)2 cells respectively) allowed identification of 22,096 different transcripts. In activated T(h)1 cells, many of the known genes (12 genes, P: < 0.01; 56 genes, P: < 0.05), including genes encoding IFN-gamma, lymphotactin, osteopontin, MIP-1alpha, MIP-1beta, perforin, beta-catenin and CD55, are highly expressed. On the other hand, in activated T(h)2 cells rather limited numbers of known genes (four genes, P: < 0.01; 10 genes; P: < 0.05), such as genes encoding FUS, ILF-2, IL-13 and E2-EPF, are found to be selectively expressed. The comprehensive identification of genes selectively expressed in human activated T(h)1 or T(h)2 cells should contribute to our understanding of the molecular basis of T(h)1/T(h)2-dominated human diseases and may provide genetic information to diagnose these diseases.

Microarray technology: the future of blood testing?

The increasing pace of development in molecular biological techniques during the last 10-15 years has had a direct effect on mass testing and diagnostic applications, including blood screening. Nucleic acid amplification techniques (NAT), usually based on the polymerase chain reaction (PCR), have been successfully applied to blood grouping and implemented recently in screening of blood donations for hepatitis C virus (HCV). The majority of microarray technologies involve an amplification step, yet the main benefits of this technology come from simultaneous analysis of thousands of analytes. Microarrays were developed to utilize the huge amount of information provided by genome projects, but they have clear potential in mass screening and diagnostics. The application of microarray technology may revolutionize blood testing, providing for the first time the prospect of an integrated platform for comprehensive donor and donation testing, replacing multiple individual assays. Design features of a blood-testing chip and various technologies with potential application in this field are discussed in this review.

Molecular profiling of human cancer

Traditionally, tumours have been categorized on the basis of histology. However, the staining pattern of cancer cells viewed under the microscope is insufficient to reflect the complicated underlying molecular events that drive the neoplastic process. By surveying thousands of genes at once, using DNA arrays, it is now possible to read the molecular signature of an individual patient's tumour. When the signature is analysed with clustering algorithms, new classes of cancer emerge that transcend distinctions based on histological appearance alone. Using DNA arrays, protein arrays and appropriate experimental models, the ultimate goal is to move beyond correlation and classification to achieve new insights into disease mechanisms and treatment targets.

Multiplexed particle-based flow cytometric assays

Several methods have been developed to quantify soluble analytes in biological fluids and tissue culture samples, including bioassays, ELISA, RPA and PCR. However, each of these techniques possesses one or more significant limitations; ELISA will only measure one analyte as a time; PCR does not detect native protein. The recent development of particle-based flow cytometric assays has raised hopes that many of these limitations can be overcome. The technology utilizes microspheres as the solid support for a conventional immunoassay, affinity assay or DNA hybridization assay which are subsequently analyzed on a flow cytometer. Several multiplexed bead systems are currently marketed by different vendors. We have used the Luminex FlowMetrix system which consists of 64 different bead sets manufactured with uniform, distinct proportions of red and orange fluorescent dyes (detected by FL2/FL3 on a FACScan). Each bead set forms the basis of an individual assay using a green fluorescent reporter dye (FL1). This system facilitates the development of multiplexed assays that simultaneously measure many different analytes in a small sample volume. They can also be developed into rapid, 'no wash' assays that can be completed in <2 h. This review traces the historical association between microspheres and flow cytometry, the development and use of particle-based flow cytometric assays, how they compare with current assays and potential future developments of this very exciting technology.