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

Polymeric Coating of Silica Microspheres for Biological Applications: Suppression of Non-Specific Binding and Functionalization with Biomolecules

The use of micro- and nanoparticles in biological applications has dramatically grown during the last few decades due to the ease of protocols development and compatibility with microfluidics devices. Particles can be composed by different materials, i.e., polymers, inorganic dielectrics, and metals. Among them, silica is a suitable material for the development of biosensing applications. Depending on their final application, the surface properties of particles, including silica, are tailored by means of chemical modification or polymeric coating. The latter strategy represents a powerful tool to create a hydrophilic environment that enables the functionalization of particles with biomolecules and the further interaction with analytes. Here, the use of MCP-6, a dimethylacrylamide (DMA)-based ter-copolymer, to coat silica microspheres is presented. MCP-6 offers unprecedented ease of coating, imparting silica particles a hydrophilic coating with antifouling properties that is able to provide high-density immobilization of biological probes.

Choice of immunoassay to evaluate porcine cytokine levels

BACKGROUND

In order to adequately monitor cytokines in experimental models, currently available methods and commercially available kits should be compared.

AIM

To compare the plasma and tissue concentrations of IL-1β, IL-6, IL-8, IL-10, and TNF as a measure of systemic inflammation in septic pigs.

METHODS

Cytokines were quantified from blood and tissue samples obtained at 0, 60, 120, 180, and 240 min, and in postmortem biopsies of the liver, kidney, lung, heart, and spleen from 26 anesthetized landrace pigs. (24 with experimental sepsis, two sham controls). Porcine-specific ELISAs (R&D) and multiplex (9-plex from Thermo Fischer, 13-plex from Millipore) immunoassays were compared.

RESULTS

The assays differed for the different cytokines and between blood and tissue. In blood, the highest concentration of TNF and IL-6 was in ELISA, IL-1β equal in ELISA and 13-plex, IL-8 in 13-plex and IL-10 in 9-plex. In tissue, the highest concentration of TNF and IL-1β was in ELISA, IL-6 and IL-8 in 13-plex and IL-10 in 9-plex.

CONCLUSION

The choice of analysis impacts the quantified cytokine responses in porcine models. ELISA and multiplex techniques supplement each other and our data suggest which assays to use for the quantification of the different cytokines.

Biocompatibility of polymer-based biomaterials and medical devices – regulations,in vitroscreening and risk-management

Biomaterials play an increasing role in modern health care systems.

Cytokines of Cervical Mucosa and Human Papilloma Virus Infection of the Cervix: A Descriptive Study

OBJECTIVE

The production of cytokines by various cervical cells can be triggered by antigenic stimuli, including human papilloma virus (HPV) infection. The aim of the present study was to evaluate differences in cytokine levels between various intraepithelial cervical lesions.

STUDY DESIGN

A total of 97 women participated in this descriptive study. Within our study population, 27 subjects presented with high-grade squamous intraepithelial lesions (HSIL), 48 with low-grade squamous intraepithelial lesion (LSIL) and 22 with a normal smear. Colposcopy and directed biopsy were performed as needed. To confirm the presence of HPV, an HPV-DNA test was performed using polymerase chain reaction. Using flow cytometry to ThinPrep cervical samples, we assessed the family of interleukins (ILs), including IL-1α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, tumor necrosis factor (TNF)-α and TNF-β and transforming growth factor-β1. Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS for Windows; version 20.0).

RESULTS

Significantly lower levels of IL-1α, IL-2, IL-4 and TNF-α were detected in cervical samples obtained from the LSIL group when compared to samples obtained from the HSIL group.

CONCLUSION

Significant differences in tissue cytokine levels exist between intraepithelial cervical lesions obtained from patients presenting with HSIL versus LSIL.

Low CD40L levels and relative lymphopenia in narcoleptic patients

Narcolepsy has been studied as a possible autoimmune disease for many years, and recent findings lend more credence to this belief. Although recent and important advances have been done, no study has analyzed the role of the CD40L in patients with narcolepsy. The purpose of this study was to assess CD40L levels, CD3, TCD4, TCD8, CD19, and CD56 lymphocytes, as well as levels of tumor necrosis factor-α and interleukin-6 in narcoleptic patients. We quantified the levels of CD40L, different types of lymphocytes, and levels of tumor necrosis factor-α and interleukin-6 in narcoleptic patients and control subjects. Narcoleptic patients had lower levels of CD40L. Total lymphocytes; CD3, and TCD4 were lower than in the control group. Our findings highlight the important role of CD40L in narcolepsy.

Simultaneous detection of serum immunoglobulin G antibodies to Cryptosporidium parvum by multiplex microbead immunoassay using 3 recognized specific recombinant C. parvum antigens

Cryptosporidiosis is a significant diarrheal disease in both humans and other mammals worldwide. In the present study, we established and validated a multiplex microbead immunoassay (MIA) for surveillance of Cryptosporidium parvum infections. In the multiplex MIA, 3 specific recombinant proteins, CP23, SA35, and SA40, were used as the capture antigens simultaneously. The antibody directed against CP23 is an index of historic infection, and those against SA35 and SA40 are indices of recent infection. The multiplex MIA yielded essentially identical results with that of monoplex MIA using these 3 recombinant proteins, and the reproducibility of the multiplex MIA results was high when standardized with a calibration curve. With multiplex MIA, we detected that the pediatric population showed a higher percentage of recent infections (seropositive rates of antibodies directed against CP23, SA35, and SA40 were 6.28%, 23.19%, and 22.71%, respectively, n = 207), whereas the adult population showed a higher percentage of historic infections (seropositive rates of antibodies directed against CP23, SA35, and SA40 were 24.40%, 11.48%, and 16.75%, respectively, n = 209).

Quantification of vascular endothelial growth factor, interleukin-8, and basic fibroblast growth factor in plasma of cancer patients and healthy volunteers - comparison of ELISA and microsphere-based multiplexed immunoassay

BACKGROUND

Vascular endothelial growth factor (VEGF), interleukin-8 (IL-8) and basic fibroblast growth factor (basic FGF) are angiogenic growth factors which may be useful as biomarkers in drug development, where they could give early information on the antiangiogenic activity of novel anticancer compounds.

METHODS

We compared two commercially available assays, enzyme linked immunosorbent assay (ELISA) and a multiplexed bead-based immunoassay (xMAP), for the quantification of these factors in plasma samples from more than 100 cancer patients and healthy individuals.

RESULTS

For VEGF and IL-8, but not for basic FGF, xMAP was more sensitive than the respective ELISA. This was true for healthy subjects as well as for cancer patients. Intraassay precision was comparable between both assay formats. Linear regression analysis of VEGF concentrations demonstrated a good correlation between ELISA and xMAP. Bland-Altman analysis showed a systematic difference between both assays, with ELISA giving higher concentration values. VEGF levels were higher in female volunteers, and both assays were able to detect this difference.

CONCLUSIONS

Multiplexed microsphere-based immunoassays have the potential to substitute ELISA for the detection of proangiogenic growth factors in clinical studies. Their shorter assay times and their ability to quantify multiple analytes in a small sample volume are advantageous.

Multiplexed microsphere-based flow cytometric immunoassays

Multiplexed microsphere-based immunoassays can be developed to simultaneously measure multiple analytes in a biologic system by flow cytometric resolution of spectrally distinct microspheres coupled with capture molecules and reporter fluorochromes bound to detection antibodies. A multiplexed sandwich immunoassay is based on an ELISA format that is transferred directly to microspheres to quantitate multiple antigens. These assays require smaller sample volumes, are less expensive, and are as reproducible, reliable, and sensitive as ELISAs. However, potential cross-reactivities between multiplexed antibodies, antigens, and specimens need to be systematically eliminated during the validation process. Sandwich and competitive immunoassays, which require only one antigen-specific antibody, can be combined in the same multiplexed array. Antibody-capture immunoassays are used to detect multiple antibodies from a specimen for diagnostic or surveillance purposes. The protocols for these three multiplexed immunologic assays are accompanied by methods for coupling analytes to microspheres and biotinylation of antibodies with a water-soluble derivative.

Multiple cytokine analysis in human tears: an optimized procedure for cytometric bead-based assay

PURPOSE

To compare instruments and reagents used for cytometric bead-based assay (CBA) of cytokines in human tears.

METHODS

Two CBA instruments and reagent kits from five vendors were compared in parallel. Vendor protocols were modified to accommodate tear volumes. Precision, recovery, dilution linearity, and stability were evaluated.

RESULTS

Luminextrade mark and Bio-Radtrade mark proved optimal for tear CBA. Good correlation for dilution linearity was observed (r > 0.80, p < 0.05) for 1-4-mu l sample volumes. Samples were stable for 30 min at 25 degrees C.

CONCLUSION

Many tear cytokines can be reliably measured by CBA using an optimized protocol. Concentrations remain stable during periods consistent with collection.

Layer-by-layer coated digitally encoded microcarriers for quantification of proteins in serum and plasma

The "layer-by-layer" (LbL) technology has been widely investigated for the coating of flat substrates and capsules with polyelectrolytes. In this study, LbL polyelectrolyte coatings applied at the surface of digitally encoded microcarriers were evaluated for the quantitative, sensitive, and simultaneous detection of proteins in complex biological samples like serum, plasma, and blood. LbL coated microcarriers were therefore coupled to capture antibodies, which were used as capture agents for the detection of tumor necrosis factor (TNF-alpha), P24, and follicle stimulating hormone (FSH). It was found that the LbL coatings did not disassemble upon incubating the microcarriers in serum and plasma. Also, nonspecific binding of target analytes to the LbL coating was not observed. We showed that the LbL coated microcarriers can reproducibly detect TNF-alpha, P24, and FSH down to the picogram per milliliter level, not only in buffer but also in serum and plasma samples. Microcarrier-to-microcarrier intratube variations were less then 30%, and interassay variations less than 8% were observed. This paper also shows evidence that the LbL coated digitally encoded microcarriers are ideally suited for assaying proteins in "whole" blood in microfluidic chips, which are of high interest for "point-of-care" diagnostics.

Association between Inflammation-Associated Cytokines, Serum Albumins, and Mortality in the Elderly

OBJECTIVE

To investigate the association between serum albumin, prealbumin, various serum inflammation associated-cytokines, and mortality in older geriatric recuperative care patients.

DESIGN

A prospective cohort study.

SETTING

A geriatric rehabilitation unit of a university-affiliated Department of Veterans Affairs hospital.

PARTICIPANTS

Participants were 53 geriatric patients (mean age 78 +/- 7.3, 96% male) admitted to a Geriatric Evaluation and Management (GEM) unit. Patients with documented near-terminal medical disorder, overt infections, and any systemic or localized inflammatory disorders were excluded.

MEASUREMENTS

Inflammation-associated cytokines (IL-8, IL-1beta, IL-6, IL-10, TNF-alpha), albumin, prealbumin, and C-reactive protein were measured at hospital discharge and each subject was then tracked for 1 year.

MAIN RESULTS

By Cox Proportional-Hazards Regression analysis, the strongest predictor of mortality within 6 months of study entry was the serum IL-6. For each log increase in IL-6, there was nearly a 9-fold greater 6-month mortality risk (RR 8.99, 95% CI 1.65 to 49.03). The association between albumin and mortality was no longer significant after controlling for IL-6. There was a strong inverse correlation between IL-6 and both albumin (R2 0.39, P < .001) and prealbumin (R2 0.41, P < .001).

CONCLUSION

Subclinical inflammation appears to be an important factor contributing to low serum albumins in older recuperative care patients and may confound the association between albumin and mortality in this population. More in-depth studies of these associations are warranted.

The xMAP™ technique can be used for detection of the inflammatory cytokines IL-1β, IL-6 and TNF-α in bovine samples

Infectious diseases can cause large health problems in cattle. The infections cause an acute inflammatory response, mediated by pro-inflammatory cytokines such as IL-1beta, IL-6 and TNF-alpha. By mapping the pattern of cytokines during inflammations, valuable information about the course of an infection is gained. The aim of the present study was to evaluate a particle-based flow cytometric method, the xMAP technique, using ovine/bovine reagents, for quantification of IL-1beta, IL-6 and TNF-alpha, for application in studies on ruminant infectious diseases with emphasis on bovine milk and plasma samples. Singleplex, duplex and triplex xMAP assays were evaluated, and limits of detection (LODs) as well as intra- and inter-assay variabilities were determined for each assay. Cross-reactivity between reagents in multiplex assays was also tested. In addition, presence of cytokines in milk and plasma samples from healthy and mastitic cows was studied. The LODs were significantly lower for singleplex xMAP assays than for duplex and triplex assays. In singleplex assays, the LODs were 0.08, 0.2 and 0.5 ng/ml, for IL-1beta, IL-6 and TNF-alpha, respectively. Corresponding LODs in triplex assays were 2.0, 6.5 and 3.5 ng/ml. Data indicate that the linear ranges of the multiplex assays were narrower than in singleplex assays. The intra-assay coefficients of variation were < or =10.7% for singleplex assays, while they ranged from 6.2 to 23.2% in the triplex assay. The inter-assay variance ranged from 5.1 to 35.8% in singleplex assays, and from 8.8 to 78.4% in triplex assays. Cross-reactivity between reagents was not observed, and all three cytokines were detected in bovine milk and plasma samples collected from cows with clinical mastitis. In conclusion, our results show that the xMAP technique can be used for quantification of IL-1beta, IL-6 and TNF-alpha in bovine samples, and that further work is required to optimize the multiplex assays.

Simultaneous quantification of 17 immune mediators in aqueous humour from patients with corneal rejection

PURPOSE

To simultaneously quantitate and compare the concentrations of 17 immune mediators: (1) the cytokines interleukin-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-10, IL-12p70, IL-13, IL-17, tumour necrosis factor-alpha, interferon-gamma; (2) the growth factors granulocyte-monocyte colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF), and (3) the chemokines CXCL-8, monocyte chemoattractant protein-1, and macrophage inflammatory protein-1beta in aqueous humour from patients with corneal rejection and patients with a non-inflammatory condition in the anterior chamber.

METHODS

Aqueous humour was obtained by paracentesis of the anterior chamber in 14 patients with corneal rejection, three patients with cataract and six patients with Fuchs' endothelial dystrophy. Simultaneous quantitation of 17 mediators in 25 micro l aqueous humour from each patient was performed by employing a highly sensitive Luminex 100 multiplex array assay.

RESULTS

All 17 immune mediators were detected in aqueous humour from rejection patients. The ranges of the immune mediators were determined. The immune mediators were significantly increased in aqueous humour from rejection patients compared with that from other patients.

CONCLUSIONS

The Luminex 100 multiplex array assay is very efficient in simultaneous quantitation of multiple immune mediators in small volumes of aqueous humour. A total of 17 immune mediators were increased in aqueous humour from rejection patients. This underlines the complex immunological interactions of the rejection process.

Multiplexed and microparticle-based analyses: quantitative tools for the large-scale analysis of biological systems

While the term flow cytometry refers to the measurement of cells, the approach of making sensitive multiparameter optical measurements in a flowing sample stream is a very general analytical approach. The past few years have seen an explosion in the application of flow cytometry technology for molecular analysis and measurements using microparticles as solid supports. While microsphere-based molecular analyses using flow cytometry date back three decades, the need for highly parallel quantitative molecular measurements that has arisen from various genomic and proteomic advances has driven the development in particle encoding technology to enable highly multiplexed assays. Multiplexed particle-based immunoassays are now common place, and new assays to study genes, protein function, and molecular assembly. Numerous efforts are underway to extend the multiplexing capabilities of microparticle-based assays through new approaches to particle encoding and analyte reporting. The impact of these developments will be seen in the basic research and clinical laboratories, as well as in drug development.

Comparison of a multiplex, bead-based fluorescent assay and immunofluorescence methods for the detection of ANA and ANCA autoantibodies in human serum

Detection of antinuclear (ANA) and antineutrophil cytoplasmic (ANCA) antibodies is extensively used for establishing a diagnosis in patients with clinical features suggestive of autoimmune disorders. The most common methods for the identification of positive patients' sera for ANA or ANCA are indirect immunofluorescence (IIF) and ELISA-based procedures. Considerable effort has been made in developing simpler automated assays for routine laboratory use. Recently a commercially available microsphere-based fluorescent assay has been introduced for the detection of ANA and ANCA. The aim of this study was to compare this technology with routinely used IIF and ELISA procedures, in patients with a suggested autoimmune disorder. A highly significant correlation between ELISA procedures for specific antibodies and the microsphere-based assays were obtained for both ANA and ANCA as well as for extractable nuclear antigens ELISA screening, indicating that multiplex technology could replace individual ELISA tests for the measurement of specific autoantibodies. However, a low sensitivity for identifying IIF-positive cases was obtained for both ANA (58.0%) and ANCA (59.1%), although there was a significant correlation between the assays. In conclusion, our data show that a microsphere-based fluorescent assay may be a valid platform for the simultaneous determination of circulating individual ANA and ANCA autoantibodies. Furthermore, multiplexing technology offers several advantages that will probably make it an attractive tool in the future. Nevertheless, until further studies are conducted that determine the clinical performance of the multiplex technology, the initial screening of patients for autoantibodies with IIF is still considered necessary.

Validation and comparison of luminex multiplex cytokine analysis kits with ELISA: determinations of a panel of nine cytokines in clinical sample culture supernatants

PROBLEM

Analyses of the expression pattern of multiple cytokines are frequently required for characterization of the status of the immune system as it pertains to Th type bias and intrinsic levels of inflammation. Classically, analysis of cytokine expression patterns has been performed by enzyme-linked immunosorbent assays (ELISA) for each separate analyte. A new technology, Luminex MAP, facilitates the simultaneous evaluation of multiple immune mediators with advantages of higher throughput, smaller sample volume, and lower cost. Validation of this technology has been limited to small sample sets, limited use of clinical study specimens, and use of non-commercial reagents.

METHODS

Ninety-six specimens from women over the course of their respective pregnancies were evaluated for cytokine concentrations using commercially available ELISA kits and commercially available Luminex MAP kits according to the manufacturers' directions. Correlations between data sets were evaluated using Pearson's correlation coefficient (r).

RESULTS

Excellent correlations were demonstrated for IL-1 beta, IL-4, IL-5, IL-6, IL-10, IFN gamma, and TNF alpha, in contrast to IL-12 p 70 and IL-13.

CONCLUSIONS

Luminex multiplex technology has distinct advantages and is a valid alternative method to ELISA for the evaluation of the majority of cytokines tested and for the characterization of immune system status.

HPV-16 L1 VLP vaccine elicits a broad-spectrum of cytokine responses in whole blood

Here, we evaluated innate and adaptive immune system cytokine responses induced by HPV-16 L1 VLP in whole blood (WB) cultures from individuals receiving the vaccine (n=20) or placebo (n=4) before and after vaccination. 11 cytokines were measured: IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IFN-gamma, TNF-alpha, and GM-CSF using multiplex bead arrays. Cytokine profiles from WB samples clearly discriminated between vaccine and placebo recipients and between pre and post-vaccination responses. Significant increases in Th1, Th2 and inflammatory cytokines were observed in WB assays following vaccination. Results from WB assays were compared against parallel PBMC-based assays in a subset of patients. Differences between whole blood assay and PBMC were observed, with the highest levels of induction found for WB for several cytokines. Our results indicate that multiplex assays for cytokine profiling in WB are an efficient tool for assessing broad spectrum, innate and adaptive immune responses to vaccines and identifying immunologic correlates of protection in efficacy studies.

Development of a sensitive microarray immunoassay and comparison with standard enzyme-linked immunoassay for cytokine analysis

Cytokine and cytokine inhibitors represent important components of the inflammatory response in patients with trauma, shock, and sepsis. Many investigators wish to quantify cytokines and it would be advantageous to measure multiple cytokines in a multiplex manner to obtain an inflammatory profile rather than a single value. Using the well-accepted standard enzyme-linked immunoassay (ELISA) as a basis, a microarray immunoassay (MI) was designed to measure 16 different human cytokines simultaneously. The MI was performed by spotting antibodies on nitrocellulose pads affixed to glass slides. Detection of the mediators was performed with biotin-conjugated antibodies followed by fluorescently labeled streptavidin. All antibodies and other reagents were purchased commercially. The MI achieved a lower limit of detection that was generally similar to traditional ELISAs (approximately 4-12 pg/mL) and also had a similar coefficient of variation. In the multiplexed MI, there was no cross reactivity between mediators. To verify the utility of the MI, cytokines and cytokine inhibitors were measured in endotoxin stimulated human blood by both ELISA and MI. Virtually identical cytokine concentrations were measured by both methods. These results describe the development of a sensitive, specific and cost-effective multiplexed microarray immunoassay that produces values similar to traditional ELISAs.

Validation and comparative analysis of a multiplexed assay for the simultaneous quantitative measurement of Th1/Th2 cytokines in human serum and human peripheral blood mononuclear cell culture supernatants

There is increasing evidence suggesting a relationship between cytokine levels and disease pathogenesis, which has led to interest in analyzing multiple cytokines in biological fluids and culture supernatants for various research and clinical studies. The introduction of methodologies allowing simultaneous measurement of interrelated biomarkers/cytokines has further revolutionized this process. In contrast to tissue culture supernatant, the measurement of cytokines in serum has proven to be difficult to characterize in multiplexed formats because of the presence of large dynamic concentration ranges of proteins and other interfering factors that are present in this matrix. In the present study, we have used the microsphere-based multiplex method to simultaneously quantitate and compare six analytes, encompassing a representation of the Th1/Th2 cytokine panel (interleukin (IL)-2, IL-4, IL-5, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and IL-10), in both serum and culture supernatants from peripheral blood mononuclear cells (PBMCs). A detailed validation procedure for these determinations is described along with a comparative analysis of the performance of the multiplexed assay in serum and culture supernatant matrices. Our results indicate that precision of the multiplexed assay is comparable in both culture supernatant and serum. However, the accuracy of quantification of cytokines in the serum matrix but not in culture supernatant may be compromised depending upon the cytokine being analyzed. Therefore, one must use caution when interpreting data from such complex matrices. Nevertheless, this assay format is appropriate to profile cytokines in clinical trial samples.

Cytometric bead assay of cytokines in sepsis: A clinical evaluation

BACKGROUND

The clinical relevancy of an attractive new multiparametric method, cytometric beads assay (CBA), was evaluated for the monitoring of cytokines in sepsis.

METHODS

A total of 52 samples (26 patients) were simultaneously tested by CBA and chemiluminescence (IL-6, IL-8, IL-1beta, and TNFalpha) or ELISA (IL-10, IL-12 p40, IL-12 p70, and soluble TNFalpha-RI).

RESULTS

CBA standard curves were linear from 20-5,000 ng/L except for IL-1beta (40-5,000 ng/L). IL-6 and IL-8 were detected in 41 and 48 samples (44-5,000 ng/L and 22-5,000 ng/L), respectively, and out of range in six samples. IL-10 and IL-1beta were detected in 14 and 15 samples (21-1,548 ng/L and 29-582 ng/L), respectively. TNFalpha was rarely detected, and IL-12 p70 was never detected. Accuracy and repeatability were good (CV for IL-6 was 2.1-8.7%; for IL-8 3.7-5.3%; for IL-10 2.5-9.1%; for IL-12 5.2-6.5%; for IL-1 beta 4-12%; and for TNFalpha 3-19.3%). Reproducibility of four standard curves and 20 samples (-1.1 to +1.03%) was excellent between tests done at two- to six-week intervals. CBA values were correlated (r2 > 0.89; P < 0.001) with our reference methods, but were lower on CBA (TNFalpha 45% +/- 8; IL-6 49% +/- 7), probably due to interactions with patients' serum, as confirmed by spiking diluted standards in one patient's serum with end stage renal failure and high levels of TNF soluble receptor (i.e., TNFalpha levels 34 and 21%).

CONCLUSIONS

Finally, these results suggest that IL-6, IL-8, IL-1beta, and Il-10 are clinically promising for sepsis evaluation. However, sensitivity of TNFalpha has to be improved and IL-12 p70 should be replaced with more relevant parameters such as TNF-R, procalcitonin, or neopterin.

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.

Biomarkers in drug discovery and development: from target identification through drug marketing

Biomarkers of disease play an important role in medicine and have begun to assume a greater role in drug discovery and development. The challenge for biomarkers is to allow earlier, more robust drug safety and efficacy measurements. Their role in drug development will continue to grow for the foreseeable future. For biomarkers to assume their rightful role, greater understanding of the mechanism of disease progression and therapeutic intervention is needed. In addition, greater understanding of the requirements for biomarker selection and validation, biomarker assay method validation and application, and clinical endpoint validation and application is needed. Biomarkers need to be taken into account while the therapeutic target is still being identified and the concept is being formulated. Biomarkers need to be incorporated into a continuous cycle that takes what is learned from the discovery and development of one series of biomarkers and translates it into the next series of biomarkers. Optimum biomarker development and application will require a team approach because of the multifaceted nature of biomarker selection, validation, and application, using such techniques as pharmacoepidemiology, pharmacogenetics, pharmacogenomics, and functional proteomics; bioanalytical method development and validation; disease process and therapeutic intervention assessments; and pharmacokinetic/pharmacodynamic modeling and simulation to improve and refine drug development. The potential for biomarkers in medicine and drug development will be limited by the least effective component of the processes. The team approach will minimize the potential for the least effective component to be fatal to the rest of the process. As scientific/regulatory foundations for biomarkers in medicine and drug development begin to be established, successes and applications will need to be effectively communicated with all of the stakeholders, including not only internal and external drug developers and regulators but also the medical community, to ensure that biomarkers are totally integrated into drug discovery and development as well as the practice of medicine.

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.

Flow cytometric ion detection with plasticized poly(vinyl chloride) microspheres containing selective lonophores

The use of flow cytometry as a rapid, high-throughput diagnostic tool for the analysis of ions is described. Monodisperse, uniform microspheres, which obey bulk optode theory and are governed by bulk extraction processes rather than surface phenomena, were prepared under mild, nonreactive conditions using a sonic stream particle casting apparatus. As an initial example demonstrating the utility of this approach, microspheres that contained a H+-selective fluorescent chromoionophore (ETH 5294), a cation-exchanger (NaTFPB), and either a highly sodium-selective (sodium ionophore X) or a potassium-selective ionophore (BME-44) were prepared. Separate solution analysis of sodium- and potassium-selective microspheres resulted in the generation of functional response curves using peak channel fluorescence intensities. The selectivity observed for both types of particles is sufficient for the clinical determination of Na+ and K+. Furthermore, sodium- and potassium-selective microspheres were analyzed in parallel using sodium sample solutions, resulting in the successful determination of sodium ion concentrations and providing important information about the selectivity of the potassium-selective sensors over sodium. This work demonstrates the potential applicability of flow cytometry as a means for developing multiplexed, rapid, high-throughput analyses for clinically relevant ions.

Cytokine regulation of periportal fibrosis in humans infected with Schistosoma mansoni: IFN-gamma is associated with protection against fibrosis and TNF-alpha with aggravation of disease

Hepatic periportal fibrosis, which affects 5-10% of subjects infected by Schistosoma mansoni, is caused by the T cell-dependent granuloma that develop around schistosome eggs. Experimental models of infection have shown that granuloma and fibrosis are tightly regulated by cytokines. However, it is unknown why advanced periportal fibrosis occurs only in certain subjects. The goal of the present study was to evaluate the cytokine response of S. mansoni-infected subjects with advanced liver disease in an attempt to relate susceptibility to periportal fibrosis with an abnormal production of cytokines that regulate granuloma and fibrosis. Fibrosis was evaluated by ultrasound on 795 inhabitants of a Sudanese village in which S. mansoni is endemic: advanced periportal fibrosis was observed in 12% of the population; 35% of the affected subjects exhibited signs of portal hypertension. Age (odds ratio (OR), 11.5), gender (OR, 4.2), and infection levels (OR, 2.2) were significantly (p < or = 0.01) associated with hepatic fibrosis. Cytokines produced by egg-stimulated blood mononuclear cells from 99 subjects were measured (75 with no or mild fibrosis; 24 subjects with advanced fibrosis). Multivariate analysis of cytokine levels showed that high IFN-gamma levels were associated with a marked reduction of the risk of fibrosis (p = 0.01; OR, 0.1); in contrast, high TNF-alpha levels were associated with an increased risk (p = 0.05; OR, 4.6) of periportal fibrosis. Moreover, infection levels were negatively associated with IFN-gamma production. These results with observations in experimental models strongly suggest that IFN-gamma plays a key role in the protection of S. mansoni-infected patients against periportal fibrosis, whereas TNF-alpha may aggravate the disease.