Comparing Flow Cytometry and ELISpot for Detection of IL-10, IL-6, and TNF Alpha on Human PBMCs.

ELISpot and flow cytometry are two methods often utilized side-by-side for detecting secreted and intracellular cytokines, respectively. Each application has its own advantages and challenges. ELISpot is more sensitive compared to ELISA and appears to be more consistent in detecting IL-10 production than flow cytometry. ELISpot can be used for detecting the secretion of multiple cytokines but not from the same cells simultaneously, whereas flow cytometry allows for the concurrent detection of multiple intracellular cytokines by the same cells. Flow cytometry is a convenient technique allowing for the detection of many cytokines at the same time in a population of cells. The restimulation cocktails used for cytokine detection in flow cytometry are hard on cells and lead to decreased cell viability. Using a live dead dye allows for the exclusion of dead cells when analyzing data. We illustrated the differences between ELISpot and flow cytometry by stimulating cells with two toll-like receptor (TLR) agonists, LPS or Pam3CSK4. Both activators increase production of various cytokines, including IL-10, IL-6, and TNF-alpha. The TLR2 antagonist, MMG-11, was used to inhibit this increased cytokine production. We observed some inhibition of IL-6 and IL-10 from Pam3CSK4 stimulation in the presence of MMG-11 by flow cytometry. TNF-α remains largely unchanged as its basal expression is high, but there is some reduction in the presence of MMG-11 for both methods. However, IL-10 was difficult to detect by ELISpot given the low seeding density. Overall, both ELISpot and flow cytometry are good methods for detecting secreted and intracellular cytokines, respectively, and should be used as complimentary assays.

Inhibition of DAGLß as a therapeutic target for pain in sickle cell disease.

Sickle cell disease (SCD) is the most common inherited disease. Pain is a key morbidity of SCD and opioids are the main treatment but their side effects emphasize the need for new analgesic approaches. Humanized transgenic mouse models have been instructive in understanding the pathobiology of SCD and mechanisms of pain. Homozygous (HbSS) Berkley mice express >99% human sickle hemoglobin and several features of clinical SCD including hyperalgesia. Previously, we reported that the endocannabinoid 2-arachidonoylglycerol (2-AG) is a precursor of the pro-nociceptive mediator prostaglandin E2-glyceryl ester (PGE2-G) which contributes to hyperalgesia in SCD. We now demonstrate the causal role of 2-AG in hyperalgesia in sickle mice. Hyperalgesia in HbSS mice correlated with elevated levels of 2-AG in plasma, its synthesizing enzyme diacylglycerol lipase ß (DAGLß) in blood cells, and with elevated levels of PGE2 and PGE2-G, pronociceptive derivatives of 2-AG. A single intravenous injection of 2-AG produced hyperalgesia in non-hyperalgesic HbSS mice, but not in control (HbAA) mice expressing normal human HbA. JZL184, an inhibitor of 2-AG hydrolysis, also produced hyperalgesia in non-hyperalgesic HbSS or hemizygous (HbAS) mice, but did not influence hyperalgesia in hyperalgesic HbSS mice. Systemic and intraplantar administration of KT109, an inhibitor of DAGLß, decreased mechanical and heat hyperalgesia in HbSS mice. The decrease in hyperalgesia was accompanied by reductions in 2-AG, PGE2 and PGE2-G in the blood. These results indicate that maintaining the physiological level of 2-AG in the blood by targeting DAGLß may be a novel and effective approach to treat pain in SCD.

Labeling of Phospho-Specific Antibodies with oYo-Link® Epitope Tags for Multiplex Immunostaining.

Spatial proteomics has recently garnered significant interest, as it offers to provide unprecedented insight into biological processes in both health and disease, by connecting protein expression patterns from the subcellular level to the tissue or even organism level. These high-content approaches generally rely on a high degree of multiplexing, whereby multiple proteins can be detected simultaneously. The most versatile multiplexing approaches utilize antibodies to confer specificity for various intracellular proteins of interest. Therefore, these methods must be able to differentiate many antibodies at once. In this chapter, we describe a simple and rapid approach to labeling antibodies with distinct epitope tags in a site-specific manner. This allows multiple antibodies, even from the same host species, to be uniquely identified and detected and offers a simple approach for spatial proteomic applications.

In Situ Hybridization (ISH) Combined with Immunocytochemistry (ICC) Co-detection of Phosphorylated EGFR in A431 Cultured Cells.

Antibodies have been commonly used to study protein phosphorylation since the first phospho-specific antibody was described in 1981. Antibodies can be developed so that they specifically recognize phosphorylated areas of particular proteins. In situ hybridization (ISH) is the technique where specific RNA or DNA molecules can be detected in a single cell without the need for antibodies. Using ACD's integrated Co-Detection Workflow (ICW), we have developed a protocol to use phospho-specific antibodies in combination with ISH to show co-localization of EGFR mRNA and EGFR proteins phosphorylated at different sites in tumor cells. Our protocol has been used for multiplexing Y1086 phosphorylated EGFR, Y1068 phosphorylated EGFR, and EGFR RNA in A431 human epidermoid carcinoma cells.

In Situ Hybridization (ISH) Combined with Immunohistochemistry (IHC) for Co-detection of EGFR RNA and Phosphorylated EGFR Protein in Lung Cancer Tissue.

Detection of phosphorylated proteins in tissue sections using immunohistochemistry (IHC) is a challenging task. The absence of tissue staining may be caused by either a lack of protein expression or a lack of protein activation via its phosphorylation. To address this problem, we employed Integrated Co-detection Workflow (ICW) protocol to analyze lung cancer tissue sections by combining in situ hybridization (ISH) with IHC. The target protein of interest was epidermal growth factor receptor (EGFR, also known as ErbB1 and HER1) which is the founding member of the ErbB family of receptor tyrosine kinases. Using phospho-specific antibodies specific for a phosphorylated site Y1173 of EGFR molecule allowed us to analyze IHC and ISH staining at a single cell level in lung cancer tissue. We have observed both a co-localization of IHC with ISH signals and ISH-positive cells lacking IHC labeling for phosphorylated EGFR. ICW appears to be a very powerful spatial biology technique for accurate localization of cancer cells with phosphorylated/activated and non-phosphorylated/nonactivated proteins.

A Never-Ending Journey in Search for Novel Cell Biology Techniques.

Cell techniques undergo rapid advancement across different areas of biomedical research [...].

Essential Controls for ELISpot Assay.

Nonspecific staining in ELISpot assay is a major obstacle in accurate quantification of experimental data. The appearance of nonspecific spots may be caused by different factors including cell- and immunoassay-related issues. In our study, we have shown that nonspecific spots can result from either cells or their debris sticking to the membranes in ELISpot plates, as well as by impurities in wash buffers and precipitation of aggregated detection antibodies. Although there is a growing interest in using Fluorospot assays allowing for simultaneous detection of multiple cell-secreted proteins, it appears that these fluorescence assays are more susceptible to developing nonspecific profiles resembling specific spots. In this chapter, we outline necessary ELISpot controls that need to be employed to tell the difference between bona fide spots vs. stained artifacts.

What Makes Cells Different from Other Open Access Journals.

In 2011, I was invited to serve as the Editor-In-Chief for Cells, which back then was a "new kid on the block" among open access (OA) journals.[...].

Express γ-H2AX Immunocytochemical Detection of DNA Damage.

DNA can be damaged by many environmental factors including chemical agents and ionizing radiation which induce the formation of DNA double-stranded breaks (DSBs). If DSBs are not repaired in a timely fashion this may cause the disruption of genome integrity, which can result in cancer development. Typically, DSBs are followed by phosphorylation of histone protein H2AX, a member of the H2A family. Immunocytochemical detection of phosphorylated H2AX (e.g., γ-H2AX) appears to be a useful technique for assessing DNA damage. Such an assessment is easy to do by analyzing labeling for γ-H2AX under the microscope and does not require an expensive laboratory setup. Using HeLa cells treated with camptothecin as a model, we developed an easy-to-run protocol to analyze DSBs. Our protocol can be applied to testing the potency of different chemicals to induce DSBs in different types of cells and requires around 2 h to complete.

Hapten-Anti-Hapten Technique for Two-Color IHC Detection of Phosphorylated EGFR and H2AX Using Primary Antibodies Raised in the Same Host Species.

Multiplex staining of cell and tissue sections with antibodies raised in the same host species is a serious challenge because of unwanted but inevitable cross-reactivity of secondary antibodies with irrelevant primary antibodies. Several techniques can be used to overcome this obstacle including direct labeling of primary antibodies with fluorescent tags and using tyramide signal amplification. Unfortunately these techniques either lack sensitivity, or require a long multistep protocol which can cause physical damage of specimens. As an alternative, we have developed a protocol based on conjugation of primary antibodies to small-size hapten molecules which can be detected with hapten-specific fluorescent secondary antibodies. This technique has been used for two-color labeling of Y845 phosphorylated Epidermal Growth Factor Receptor (EGFR) and S139 phosphorylated histone H2AX protein in A431 human epidermoid carcinoma cells. Our novel hapten-anti-hapten detection chemistry allows for generating a stronger fluorescent signal and completely avoid cross-interactions of secondary antibodies with irrelevant primary antibodies.

High-Sensitivity IHC Detection of Phosphorylated p27/Kip1 in Human Tissues Using Secondary Antibody Conjugated to Polymer-HRP.

A complex composed of goat anti-rabbit secondary antibody conjugated to a polymer coated with horseradish peroxidase (HRP) molecules was used to develop rapid and highly sensitive immunostaining protocol for the detection of phosphorylated p27/Kip1 (T157) in human tissues. This polymer-HRP complex produced much better sensitivity detection compared to conventional biotin-streptavidin-HRP chemistry. Using polymer-HRP made it possible to reduce primary antibody concentration, eliminate some incubation steps such as avidin-biotin blocking and incubation with separate biotinylated secondary antibodies, and shorten the incubation time with primary antibody. Specificity of the detection was confirmed by eliminating labeling after treating tissues with lambda phosphatase to remove phosphate groups from p27/Kip1. Secondary antibodies conjugated to polymer-HRP is a reagent of choice in both research and diagnostic pathology allowing detecting low abundant and weakly expressed tissue targets.

Using Phospho-Peptides Immobilized on Magnetic Beads for Absorption Control in Immunohistochemistry.

Phospho-specific primary antibodies are used in immunohistochemistry (IHC) to detect phosphorylated sequences in proteins, in some cases they may also cross-react with non- or de-phosphorylated sequences. To rule out nonspecific staining, and to determine that the staining pattern is specific it is necessary to employ a so-called absorption control: phospho-specific primary antibodies are first incubated with phospho-peptide immunogen to block antibody binding sites, and this mixture is applied to tissue sections. If the antibody pre-blocked with cognate immunogen does not produce tissue staining, then the antibody is considered specific. However, if the staining does occur, it indicates that the antibody is nonspecific. The drawback of doing absorption by mixing the peptide with the antibody is that in solution such peptide-antibody complexes can dissociate unblocking the antibody which becomes capable of binding to cell and tissue targets, producing unwanted staining. To overcome this problem, we have developed a simple absorption control technique allowing for efficient blocking of phospho-specific antibodies with phospho-peptides immobilized on magnetic beads. This technique allows for sequestration of peptide-antibody complex from the incubation mixture eliminating the risk of un-blocking primary antibodies via their dissociation from the blocking peptide.

Automated High-Content Screening of γ-H2AX Expression in HeLa Cells.

Due to their inherent nature, DNA strands can be easily broken by various environmental factors including chemical agents and ionizing radiation. Unrepaired DNA double-stranded breaks (DSBs) may result in genetic instability and have a strong negative impact on the integrity of the genome. It has been found that DSBs are always followed by phosphorylation of histone protein H2AX, a member of the H2A family, and immunocytochemical detection of phosphorylated H2AX (referred to as γ-H2AX) is one of the frequently used techniques for assessing DNA damage. Usually such an assessment is done manually under the microscope which is not practical for analyzing large numbers of cells and prevents researchers from rapid and unbiased testing of novel drug compounds. To solve this problem we attempted to do automated assessment of DSBs by using a High-Content Screening (HCS) platform. As a result of this effort, we developed an easy to run HCS protocol for accurate analysis of DSBs in HeLa cells treated with camptothecin as a model. By varying the time of camptothecin treatment and its concentration we were able to study the dynamics of DSBs and perform a statistical analysis.Results of our study indicate that DSBs can be investigated using a HCS platform that enable the analysis of large numbers of experimental data points in a fast and a highly accurate manner. The protocol presented in this chapter can be easily adapted for screening libraries containing substantial numbers of chemical compounds for their efficiency to induce or/and repair DNA breaks.

Membrane Microplates for One- and Two-Color ELISPOT and FLUOROSPOT Assays.

Membranes are widely used as protein blotting matrices for a large variety of research applications including western blotting and enzyme-linked immunospot assay (ELISPOT). The largest advantage of using membranes versus solid plastic support is the porosity of membranes allowing for immobilization of high concentrations of proteins and antibodies which, in turn, increases the sensitivity of detection. Similar to plastic surfaces, polyvinylidene difluoride (PVDF) and nitrocellulose membranes create good microenvironment for live cells cultured in vitro and do not interfere with cellular physiology. It appears that PVDF-backed microplates are a golden standard for ELISPOT assays: such plates are inexpensive, easy to use and after assay development, membranes can be removed from the plates and archived. Given the convenience and reliability of membrane microplates, they are widely used in ELISPOT assays for basic research and clinical trials. The ELISPOT assay is an antibody "sandwich" technique aimed at trapping cell-secreted molecules between capture and detection antibodies, followed by either chromogenic enzymatic or fluorescence detection. This review covers the principles of the ELISPOT assay on membrane microplates including single-color and two-color detection techniques with the emphasis on assay design, choosing membrane microplates, and troubleshooting protocols.

Comparative Multi-Donor Study of IFNγ Secretion and Expression by Human PBMCs Using ELISPOT Side-by-Side with ELISA and Flow Cytometry Assays.

ELISPOT, ELISA and flow cytometry techniques are often used to study the function of immune system cells. It is tempting to speculate that these assays can be used interchangeably, providing similar information about the cytokine secreting activity of cells: the higher the number of cytokine-positive cells measured by flow cytometry, the higher the number of cytokine-secreting cells expected to be detected by ELISPOT and the larger the amount of secreted cytokine expected to be measured by ELISA. We have analyzed the expression level and secretion capacity of IFNγ from peripheral blood mononuclear cells isolated from five healthy donors and stimulated by calcium ionomycin mixed with phorbol 12-myristate 13-acetate in a non-specific manner in side-by-side testing using ELISPOT, ELISA and flow cytometry assays. In our study, we observed a general correlation in donors' ranking between ELISPOT and flow cytometry; ELISA values did not correlate with either ELISPOT or flow cytometry. However, a detailed donor-to-donor comparison between ELISPOT and flow cytometry revealed significant discrepancies: donors who have similar numbers of IFNγ-positive cells measured by flow cytometry show 2-3-fold differences in the number of spot-forming cells (SFCs) measured by ELISPOT; and donors who have the same number of SFCs measured by ELISPOT show 30% differences in the number of IFNγ-positive cells measured by flow cytometry. Significant discrepancies between donors were also found when comparing ELISA and ELISPOT techniques: donors who secreted the same amount of IFNγ measured by ELISA show six-fold differences in the number of SFCs measured by ELISPOT; and donors who have 5-7-times less secreted IFNγ measured by ELISA show a two-fold increase in the number of SFCs measured by ELISPOT compared to donors who show a more profound secretion of IFNγ measured by ELISA. The results of our study suggest that there can be a lack of correlation between IFNγ values measured by ELISPOT, ELISA and flow cytometry. The higher number of cytokine-positive cells determined by flow cytometry is not necessarily indicative of a higher number of cytokine-secreting cells when they are analyzed by either ELISPOT or ELISA. Our ELISPOT vs. ELISA comparison demonstrates that the higher number of SFCs observed in ELISPOT does not guarantee that these cells secrete larger amounts of cytokines compared to donors with lower SFC numbers. In addition, our data indicate that ELISPOT, ELISA and flow cytometry should be performed as complementary, rather than stand-alone assays: running these assays in parallel on samples from the same donors may help to better understand the mechanisms underlying the physiology of cytokine-secreting cells.

Putative kappa opioid heteromers as targets for developing analgesics free of adverse effects.

It is now generally recognized that upon activation by an agonist, ß-arrestin associates with G protein-coupled receptors and acts as a scaffold in creating a diverse signaling network that could lead to adverse effects. As an approach to reducing side effects associated with κ opioid agonists, a series of ß-naltrexamides 3-10 was synthesized in an effort to selectively target putative κ opioid heteromers without recruiting ß-arrestin upon activation. The most potent derivative 3 (INTA) strongly activated KOR-DOR and KOR-MOR heteromers in HEK293 cells. In vivo studies revealed 3 to produce potent antinociception, which, when taken together with antagonism data, was consistent with the activation of both heteromers. 3 was devoid of tolerance, dependence, and showed no aversive effect in the conditioned place preference assay. As immunofluorescence studies indicated no recruitment of ß-arrestin2 to membranes in coexpressed KOR-DOR cells, this study suggests that targeting of specific putative heteromers has the potential to identify leads for analgesics devoid of adverse effects.

Bivalent ligands that target µ opioid (MOP) and cannabinoid1 (CB1) receptors are potent analgesics devoid of tolerance.

Given that µ opioid (MOP) and canabinoid (CB1) receptors are colocalized in various regions of the central nervous system and have been reported to associate as heteromer (MOP-CB1) in cultured cells, the possibility of functional, endogenous MOP-CB1 in nociception and other pharmacologic effects has been raised. As a first step in investigating this possibility, we have synthesized a series of bivalent ligands 1-5 that contain both µ agonist and CB1 antagonist pharmacophores for use as tools to study the functional interaction between MOP and CB1 receptors in vivo. Immunofluorescent studies on HEK293 cells coexpressing both receptors suggested 5 (20-atom spacer) to be the only member of the series that bridges the protomers of the heteromer. Antinociceptive testing in mice revealed 5 to be the most potent member of the series. As neither a mixture of monovalent ligands 9 + 10 nor bivalents 2-5 produced tolerance in mice, MOR-CB1 apparently is not an important target for reducing tolerance.

An immunocytochemical-derived correlate for evaluating the bridging of heteromeric mu-delta opioid protomers by bivalent ligands.

Bivalent ligands that contain two pharmacophores linked by a spacer are promising tools to investigate the pharmacology of opioid receptor heteromers. Evidence for occupation of neighboring protomers by two phamacophores of a single bivalent ligand (bridging) has relied mainly on pharmacological data. In the present study, we have employed an immunocytochemical correlate to support in vivo biological studies that are consistent with bridging. We show that a bivalent mu agonist/delta antagonist (MDAN-21) that is devoid of tolerance due to possible bridging of mu and delta protomers prevents endocytosis of the heteromeric receptors in HEK-293 cells. Conversely, a bivalent ligand (MDAN-16) with a short spacer or monovalent mu agonist give rise to robust internalization. The data suggest that the immobilization of proximal mu and delta protomers is due to bridging by MDAN-21. The finding that MDAN-21 and its shorter spacer homologue MDAN-16 possess equivalent activity in HEK-293 cells, but produce dramatically divergent internalization of mu-delta heteromer, is relevant to the role of internalization and tolerance.

Equine ELISPOT assay to study secretion of IFNγ and IL-4 from peripheral blood mononuclear cells.

Human and mouse immune system cells are the most frequently used specimens in ELISPOT assays. In an effect to expand the application of ELISPOT assay to other species, we developed matched antibody pairs for ready-to-use kits designed for studying the frequency of equine IFNγ- and IL-4-secreting peripheral blood mononuclear cells (PBMCs). Equine PBMCs were stimulated with either concanavalin A (Con A) or calcium ionomycin mixed with phorbol 12-myristate 13-acetate (CaI + PMA). We found that Con A, in general, had a more profound stimulating effect than CaI + PMA on IL-4 secretion, whereas both stimulatory and inhibitory effects were observed on IFNγ secretion. Our data demonstrate a large dynamic range in IFNγ and IL-4 secretion among different donors, which may reflect animal health and serve as a valuable diagnostic marker.

ELISPOT assay as a tool to study oxidative stress in lymphocytes.

Enzyme-linked immuno spot (ELISPOT) assay is widely used for vaccine development, cancer and AIDS research, and autoimmune disease studies. The output of ELISPOT assay is a formation of colored spots which appear at the sites of cells releasing cytokines, with each individual spot representing a single cytokine-releasing cell. We worked out a protocol to study oxidative stress in human peripheral blood lymphocytes by determining their potency to secrete IFN-gamma, IL-2, IL-4, IL-5, IL-8, and TNF-alpha in response to acute treatment with hydrogen peroxide. We show that hydrogen peroxide-induced oxidative stress can cause a ∼twofold decrease in the number of lymphocytes secreting the TH1 cytokines IFN-gamma and IL-2, as well as chemokines IL-8 and TNF-alpha. However, the number of cells secreting TH2 cytokines IL-4 and IL-5 in hydrogen -peroxide-treated group did not change. It appears that oxidative stress may affect TH1-TH2 cytokine secretion -balance which, in turn, may underlie developments of various pathological conditions. This protocol can be easily modified to study the effects of many other oxidative stress compounds.