Basic principles of flow cytometry

Shedding Light on Intracellular Proteins using Flow Cytometry

Intracellular protein abundance is routinely measured in mammalian cells using population-based techniques such as western blotting which fail to capture single cell protein levels or using fluorescence microscopy which is although suitable for single cell protein detection but not for rapid analysis of large no. of cells. Flow cytometry offers rapid, high-throughput, multiparameter-based analysis of intracellular protein expression in statistically significant no. of cells at single cell resolution. In past few decades, customized assays have been developed for flow cytometric detection of specific intracellular proteins. This review discusses the scope of flow cytometry for intracellular protein detection in mammalian cells along with specific applications. Technological advancements to overcome the limitations of traditional flow cytometry for the same are also discussed.

Monitoring Changes in Intracellular Reactive Oxygen Species Levels in Response to Histone Deacetylase Inhibitors

Reactive oxygen species (ROS) are induced by several chemotherapeutics. In this protocol, we describe a flow cytometry-based method for the analysis of the intracellular levels of ROS in vital leukemic cells in response to the histone deacetylase inhibitor vorinostat. This measurement of ROS using the cell-permeable dye CM-H2DCFDA indicates intracellular oxidative stress.

A flow cytometric journey into cell cycle analysis

Cell cycle involves a series of changes that lead to cell growth and division. Cell cycle analysis is crucial to understand cellular responses to changing environmental conditions. Since its inception, flow cytometry has been particularly useful for cell cycle analysis at single cell level due to its speed and precision. Previously, flow cytometric cell cycle analysis relied solely on the measurement of cellular DNA content. Later, methods were developed for multiparametric analysis. This review explains the journey of flow cytometry to understand different molecular and cellular events underlying cell cycle using various protocols. Recent advances in the field that overcome the shortcomings of traditional flow cytometry and expand its scope for cell cycle studies are also discussed.

Flow cytometry: principles, applications and recent advances

Flow cytometry (FCM) is a sophisticated technique that works on the principle of light scattering and fluorescence emission by the specific fluorescent probe-labeled cells as they pass through a laser beam. It offers several unique advantages as it allows fast, relatively quantitative, multiparametric analysis of cell populations at the single cell level. In addition, it also enables physical sorting of the cells to separate the subpopulations based on different parameters. In this constantly evolving field, innovative technologies such as imaging FCM, mass cytometry and Raman FCM are being developed in order to address limitations of traditional FCM. This review explains the general principles, main applications and recent advances in the field of FCM.

Fluorochrome choices for multi-color flow cytometry

Fluorochrome selection is a key step in designing multi-color antibody panels. The list of available fluorochromes is continuously growing, fitting current needs in clinical flow cytometry to simultaneously use more markers to better define multiple leukocyte subpopulations in a single tube. Several criteria guide fluorochrome selection: i) the fluorescence profiles (excitation and emission), ii) relative brightness, iii) fluorescence overlap, iv) fluorochrome stability, and v) reproducible conjugation to antibodies. Here we used 75 samples (45 bone marrow and 30 blood) to illustrate EuroFlow strategies for evaluation of compatible fluorochromes, and how the results obtained guide fluorochrome selection as a critical step in the antibody-panel building process. Our results allowed identification of optimal fluorescence profiles (e.g. higher fluorescence intensity and/or resolution with limited fluorescence overlap into neighbor channels) for brilliant violet (BV)421 and BV510 in the violet laser and allophycocyanin (APC) hilite 7 (H7) or APC C750 in the red laser vs. other candidate fluorochromes generally applied for the same detectors and here evaluated. Moreover, evaluation of the same characteristics for another group of fluorochromes (e.g. BV605, BV650, PE CF594, AF700 or APC AF700) guided selection of the most appropriate fluorochrome conjugates to be combined in a multi-color antibody panel. Albeit this is a demanding approach, it could be successfully applied for selection of fluorochrome combinations for the EuroFlow antibody panels for diagnosis, classification and monitoring of hematological malignancies and primary immunodeficiencies. Consequently, sets of 8-, 10- and 12-color fluorochrome combinations are proposed as frame of reference for initial antibody panel design.

Liraglutide mitigates TNF-α induced pro-atherogenic changes and microvesicle release in HUVEC from diabetic women

BACKGROUND

To evaluate whether exposure to GLP-1 receptor agonist Liraglutide could modulate pro-atherogenic alterations previously observed in endothelial cells obtained by women affected by gestational diabetes (GD), thus exposed in vivo to hyperglycemia, oxidative stress, and inflammation and to evaluate endothelial microvesicle (EMV) release, a new reliable biomarker of vascular stress/damage.

METHODS

We studied Liraglutide effects and its plausible molecular mechanisms on monocyte cell adhesion and adhesion molecule expression and membrane exposure in control (C-) human umbilical vein endothelial cells (HUVEC) as well as in HUVEC of women affected by GD exposed in vitro to TNF-α. In the same model, we also investigated Liraglutide effects on EMV release.

RESULTS

In response to TNF-α, endothelial monocyte adhesion and VCAM-1 and ICAM-1 expression and exposure on plasma membrane was greater in GD-HUVEC than C-HUVEC. This was the case also for EMV release. In GD-HUVEC, Liraglutide exposure significantly reduced TNF-α induced endothelial monocyte adhesion as well as VCAM-1 and ICAM-1 expression and exposure on plasma membrane. In the same cells, Liraglutide exposure also reduced MAPK/NF-kB activation, peroxynitrite levels, and EMV release.

CONCLUSIONS

TNF-α induced pro-atherogenic alterations are amplified in endothelial cells chronically exposed to hyperglycemia in vivo. Liraglutide mitigates TNF-α effects and reduces cell stress/damage indicators, such as endothelial microvesicle (EMV) release. These results foster the notion that Liraglutide could exert a protective effect against hyperglycemia and inflammation triggered endothelial dysfunction.

Endothelial microparticles as conveyors of information in atherosclerotic disease

Endothelial microparticles (EMPs) are complex submicron membrane-shed vesicles released into the circulation following endothelium cell activation or apoptosis. They are classified as either physiological or pathological, with anticoagulant or pro-inflammatory effects respectively. Endothelial dysfunction caused by inflammation is a key initiating event in atherosclerotic plaque formation. Athero-emboli, resulting from ruptured carotid plaques are a major cause of stroke. Current clinical techniques for arterial assessment, angiography and carotid ultrasound, give accurate information about stenosis but limited evidence on plaque composition, inflammation or vulnerability; as a result, patients with asymptomatic, or fragile carotid lesions, may not be identified and treated effectively. There is a need to discover novel biomarkers and develop more efficient diagnostic approaches in order to stratify patients at most risk of stroke, who would benefit from interventional surgery. Increasing evidence suggests that EMPs play an important role in the pathogenesis of cardiovascular disease, acting as a marker of damage, either exacerbating disease progression or triggering a repair response. In this regard, it has been suggested that EMPs have the potential to act as biomarkers of disease status. In this review, we will present the evidence to support this hypothesis and propose a novel concept for the development of a diagnostic device that could be implemented in the clinic.

Microparticles in health and disease

Microparticles (MPs), small membrane-derived vesicles, are derived from many cell types and released into the circulation. Microparticles can express antigens, and contain cell surface proteins, cytoplasmic contents, and nuclear components from their cell of origin that determines their composition, characterization, and transfer of biologic information. Certain prompts for this release include shear stress, complement activation, proapoptotic stimulation, cellular damage, or agonist interaction with cell surface receptors. Release can be physiologic or pathologic and is associated with proinflammatory and procoagulant effects and has been implicated in thrombotic states. Microparticles also contribute to systemic inflammation and cardiovascular, hematologic, and oncologic disease states. The study of MPs in human medicine is rapidly advancing and extends into the physiology of health, the pathophysiology of disease, and the role of MPs in transfusion medicine. In veterinary medicine, published work on MPs has been limited to the area of inherited disorders, blood storage, and leukoreduction (LR). Microparticle research is still in its infancy, and this review should be seen as a snapshot of what is currently known. As research continues important limitations, including variations in preanalytic variables such as collection, storage, or centrifugation, and limitations of quantitation are coming to the forefront. Correlation of quantitation of MPs with assays of activity will hopefully shed light on the true nature of MPs in health and disease. This review will focus on the role of cellular exocytic vesiculation in health, disease, and transfusion medicine.

FlowFP: A Bioconductor Package for Fingerprinting Flow Cytometric Data

A new software package called flowFP for the analysis of flow cytometry data is introduced. The package, which is tightly integrated with other Bioconductor software for analysis of flow cytometry, provides tools to transform raw flow cytometry data into a form suitable for direct input into conventional statistical analysis and empirical modeling software tools. The approach of flowFP is to generate a description of the multivariate probability distribution function of flow cytometry data in the form of a “fingerprint.” As such, it is independent of a presumptive functional form for the distribution, in contrast with model-based methods such as Gaussian Mixture Modeling. FlowFP is computationally efficient and able to handle extremely large flow cytometry data sets of arbitrary dimensionality. Algorithms and software implementation of the package are described. Use of the software is exemplified with applications to data quality control and to the automated classification of Acute Myeloid Leukemia.

Flow cytometry as a tool for measurement of steroid hormone receptor protein expression in leukocytes

Measurement of protein expression in live, intact cells using flow cytometry (FC) has been employed for several decades in the areas of immunology, cell biology, and molecular biology. More recently, this technique has found appreciation in applied scientific fields, including cancer biology and endocrinology, to serve as a tool for identifying cells more likely to respond to specific treatments. FC, also referred to as fluorescence-activated cell sorting (FACS), is an antibody-based method that provides the user with an ability to identify proteins expressed on surfaces of cells as well as in the cytoplasm, including steroid hormone receptors. This technique is most useful for examining specific cell types in a heterogeneous population and therefore can be used to identify cells more likely to respond to treatments based on expression of the appropriate receptor. Isolation of purified subpopulations for further manipulation and investigation of functional capacity is also possible using a cell sorter, which uses similar technology to isolate cells for use by the researcher. This is especially important for studying responses of less abundant cell populations in tissues that express high levels of a target protein or receptor of interest. Furthermore, FACS analysis is clinically useful to identify and isolate responsive cell populations, which may be less appreciable in whole tissues because of the diluting effects of surrounding, nonresponding cell types. Immune cells are commonly utilized as a source of cell populations in the FC technique and have previously been shown to express steroid hormone receptors and respond to steroid hormone treatment. Here, we demonstrate that FC is a useful tool for identifying immune cells expressing steroid hormone receptor protein. This method can also be easily expanded to include other, nonimmune cell populations to address specific research questions related to steroid hormone receptor biology.

Contagem de reticulócitos de cães saudáveis ou anêmicos pela citometria de fluxo

Compararam-se os resultados da contagem de reticulócitos pela microscopia de luz e pelo método da citometria de fluxo em 25 cães saudáveis (controle), 60 cães com anemia regenerativa e 40 com anemia arregenerativa. Houve diferença nas contagens absolutas obtidas pela microscopia de luz e pela citometria de fluxo nos três grupos estudados. A contagem de reticulócitos foi mais alta pela citometria de fluxo que a contagem pela microscopia de luz, mostrando ser um método mais sensível, simples e seguro para a quantificação de reticulócitos.

Evaluation of steroid hormone receptor protein expression in intact cells using flow cytometry

Several methods are currently employed to evaluate expression of steroid hormone receptors in tissues and cells, including real-time reverse-transcriptase polymerase chain reaction (real-time RT-PCR) and western blot assays. These methods require homogenization of cells, thereby preventing evaluation of individual cells or specific cell types in a given tissue sample. In addition, methods such as real-time RT-PCR assess mRNA levels, which may be subject to posttranslational modifications that prevent subsequent production of functional proteins. Flow cytometry is a fluorescence-based technique commonly used to evaluate expression of cell surface and intracellular proteins. This method is especially useful as it allows for single-cell analysis and can be utilized to determine the amount of receptor expressed by individual cells. Flow cytometry is commonly used to analyze immune cell activity and determine functionality based on changes in expression of cell surface molecules, as well as intracellular proteins (such as cytokines). Here, we describe a method to identify protein expression of steroid hormone receptors by rat leukocytes from different organs (spleen, liver and thymus) using flow cytometry. We examined expression of glucocorticoid receptor (GR), androgen receptor (AR) and progesterone receptor (PR) by cells at these sites and were able to demonstrate expression of receptors, as well as the intensity of expression of each receptor. This method is useful for rapid, high throughput measurement of steroid hormone receptors at the protein level in single, intact cells and would be valuable to determine which cells are more likely to respond to steroid hormone treatment.

Isolation, purification and flow cytometric analysis of human intrahepatic lymphocytes using an improved technique

Intrahepatic lymphocytes (IHL) with their diverse and distinctive subsets emphasise the importance of the liver as a site of immunological activity, but special care is required for their isolation and characterisation. Protocols for IHL isolation, purification and FACS analysis were devised and compared with published extraction protocols. We have reduced the time that IHL are exposed to potentially damaging enzymes during extraction and purified specific subsets using monoclonal antibody (mAb)-coated magnetic microbeads. This has yielded IHL populations with higher viability than previously described protocols (92-95%, compared with 39-86%). Flow cytometric characterisation of IHL subset immunophenotypes was optimised by combining CD45 staining (fluorescence gating) with traditional light scatter properties. Using a panel of mAb and liver biopsies obtained from 23 cadaveric liver transplant donors, we show that the normal liver contains a heterogeneous IHL population with distinctive phenotypes. CD8+ IHL was the predominant population with a mean CD4/CD8 ratio of 1:1.7. Up to 40% of IHL expressed gammadeltaTCR and a third expressed CD56 NK marker; indicating a site of intense immunological activity. The techniques described will allow these cell types to be isolated, fully characterised and their physiological functions to be determined. The histologically normal liver contains heterogeneous and diverse IHL with large numbers of CD8+, NK, NKT and gammadelta+ cells.

Liquid chromatography coupled on-line to flow cytometry for postcolumn homogeneous biochemical detection

The feasibility of flow cytometry as read-out principle for homogeneous cell- or bead-based assays coupled on-line to LC is demonstrated using digoxin-coated beads (Dig-Beads) and fluorescent-labeled anti-digoxin (AD-FITC) as model system. The assay is carried out in a postcolumn continuous-flow reaction detection system where the AD-FITC and Dig-Beads are simultaneously added to the eluate of an LC separation column. Binding of AD-FITC to Dig-Beads results in a constant amount of fluorescence associated with the beads, which is detected by the flow cytometer. The presence of active compounds, such as digoxin and its analogues, in the sample will results in a decrease of the AD-FITC-Dig-Bead complex and, consequently, in the bead-associated fluorescence. Hence, the bead-associated fluorescence detected is inversely related to the digoxin concentration. A data-handling algorithm was developed in-house for adequate analysis of raw data output from the flow cytometer. Various conditions that influence the performance of this novel LC-biochemical detection (LC-BCD) system were investigated to determine the optimal settings of the bead-based biochemical interaction. The optimized flow injection bead-based assay was capable of detecting very low concentrations of digoxigenin (0.5 nmol/L), digoxin (0.1 nmol/L), and gitoxigenin (50 nmol/L). The applicability of LC coupled on-line to flow cytometry was demonstrated by the individual detection of digoxin, digoxigenin, and gitoxigenin in a single LC analysis. The successful coupling of LC on-line to flow cytometry principally enables the use of a wide range of new homogeneous assay formats in LC-BCD, such as membrane-bound receptor assays, cell-binding assays, and functional cell-based assays. Next to the ability to use insoluble targets, and also multiplexing assays, i.e., performing a number of assays simultaneously, using color- or size-coded beads becomes at hand in LC-BCD.

Molecular biology of leukemia

OBJECTIVE

To review the current tests for diagnosis and the implications of cytogenetic analysis in leukemia.

DATA SOURCES

Professional journals, books.

CONCLUSION

Leukemia is a genetic disorder with more than 500 recurring translocations. Recurrent chromosomal changes occur in more than one half of all cases of leukemia. Testing includes bone marrow biopsy and aspirate, histochemical staining, immunophenotyping, cytogenetics, and molecular markers. Characterization of specific chromosome changes provides information in determining initial therapy and post-remission therapy.

IMPLICATIONS FOR NURSING PRACTICE

Nurses must continually educate themselves to stay current with developing technology and the results of continuing research. This professional education must then be translated to the bedside throughout the continuum of care.