Flow Cytometry: The Glass Is Half Full

Noninvasive in vivo photoacoustic detection of malaria with Cytophone in Cameroon

Current malaria diagnostics are invasive, lack sensitivity, and rapid tests are plagued by deletions in target antigens. Here we introduce the Cytophone, an innovative photoacoustic flow cytometer platform with high-pulse-rate lasers and a focused ultrasound transducer array to noninvasively detect and identify malaria-infected red blood cells (iRBCs) using specific wave shapes, widths, and time delays generated from the absorbance of laser energy by hemozoin, a universal biomarker of malaria infection. In a population of Cameroonian adults with uncomplicated malaria, we assess our device for safety in a cross-sectional cohort (n = 10) and conduct a performance assessment in a longitudinal cohort (n = 20) followed for 30 ± 7 days after clearance of parasitemia. Longitudinal cytophone measurements are compared to point-of-care and molecular assays (n = 94). Cytophone is safe with 90% sensitivity, 69% specificity, and a receiver-operator-curve-area-under-the-curve (ROC-AUC) of 0.84, as compared to microscopy. ROC-AUCs of Cytophone, microscopy, and RDT compared to quantitative PCR are not statistically different from one another. The ability to noninvasively detect iRBCs in the bloodstream is a major advancement which offers the potential to rapidly identify both the large asymptomatic reservoir of infection, as well as diagnose symptomatic cases without the need for a blood sample.

From Genesis to Old Age: Exploring the Immune System One Cell at a Time with Flow Cytometry

The immune system is a highly complex and tightly regulated system that plays a crucial role in protecting the body against external threats, such as pathogens, and internal abnormalities, like cancer cells. It undergoes development during fetal stages and continuously learns from each encounter with pathogens, allowing it to develop immunological memory and provide a wide range of immune protection. Over time, after numerous encounters and years of functioning, the immune system can begin to show signs of erosion, which is commonly named immunosenescence. In this review, we aim to explore how the immune system responds to initial encounters with antigens and how it handles persistent stimulations throughout a person's lifetime. Our understanding of the immune system has greatly benefited from advanced technologies like flow cytometry. In this context, we will discuss the valuable contribution of flow cytometry in enhancing our knowledge of the immune system behavior in aging, with a specific focus on T-cells. Moreover, we will expand our discussion to the flow cytometry-based assessment of extracellular vesicles, a recently discovered communication channel in biology, and their implications for immune system functioning.

A low-cost, label-free microfluidic scanning flow cytometer for high-accuracy quantification of size and refractive index of particles

Flow cytometers and fluorescence activated cells sorters (FCM/FACS) represent the gold standard for high-throughput single-cell analysis, but their usefulness for label-free applications is limited by the unreliability of forward and side scatter measurements. Scanning flow cytometers represent an appealing alternative, as they exploit measurements of the angle-resolved scattered light to provide accurate and quantitative estimates of cellular properties, but the requirements of current setups are unsuitable for integration with other lab-on-chip technologies or for point-of-care applications. Here we present the first microfluidic scanning flow cytometer (μSFC), able to achieve accurate angle-resolved scattering measurements within a standard polydimethylsiloxane microfluidic chip. The system exploits a low cost linearly variable optical density (OD) filter to reduce the dynamic range of the signal and to increase its signal-to-noise ratio. We present a performance comparison between the μSFC and commercial machines for the label free characterization of polymeric beads with different diameters and refractive indices. In contrast to FCM and FACS, the μSFC yields size estimates linearly correlated with nominal particle sizes (R² = 0.99) and quantitative estimates of particle refractive indices. The feasibility of using the μSFC for the characterization of biological samples is demonstrated by analyzing a population of monocytes identified based on the morphology of a peripheral blood mononuclear cells sample, which yields values in agreement with the literature. The proposed μSFC combines low setup requirements with high performance, and has great potential for integration within other lab-on-chip systems for multi-parametric cell analysis and for next-generation point-of-care diagnostic applications.

Visualisation of Host-Pathogen Communication

The core of biomedical science is the use of laboratory techniques to support the diagnosis and treatment of disease in clinical settings. Despite tremendous advancement in our understanding of medicine in recent years, we are still far from having a complete understanding of human physiology in homeostasis, let alone the pathology of disease states. Indeed medical advances over the last two hundred years would not have been possible without the invention of and continuous development of visualisation techniques available to research scientists and clinicians. As we have all learned from the recent COVID pandemic, despite advances in modern medicine we still have much to learn regarding infection biology. Indeed antimicrobial resistant (AMR) bacteria are a global threat to human health, meaning research into bacterial pathogenesis is vital. In this chapter, we will briefly describe the nature of microbes and host immune responses before delving into some of the visualisation techniques utilised in the field of biomedical research with a focus on host-pathogen interactions. We will give a brief overview of commonly used techniques from gold standard staining methods, in situ hybridisation, microscopy, western blotting, microbial characterisation, to cutting-edge image flow cytometry and mass spectrometry. Specifically, we will focus on techniques utilised to visualise interactions between the host, our own bodies, and invading organisms including bacteria. We will touch on in vitro and ex vivo modelling methodology with examples utilised to delineate pathogenicity in disease. A better understanding of bacterial biology, immunology and how these fields interact (host-pathogen communications) in biomedical research is integral to developing novel therapeutic approaches which circumvent the need for antibiotics, an important issue as we enter a post-antibiotic era.

Flow Cytometry Approaches to Obtain Medulloblastoma Stem Cells from Bulk Cultures

Cancer stem cells are considered the reservoir cancer cells that are resistant to most of the forms of cancer therapies and cause relapse of the tumor. Medulloblastoma (MB), a primary CNS tumor, is a very fast-growing tumor affecting younger population. In order to characterize medulloblastoma cancer stem cells or studying the drug resistance in MB mediated through the cancer stem cells, it becomes essential to isolate and study them. Isolation and characterization of tumor cells is a critical step in understanding the cancer progression and to devise novel approaches against them as drug targets. Typically, characterization of stem cells is done through surface marker analysis and with the advent of flow cytometry based techniques, this has become incredibly straightforward. Flow cytometry employs a uniformly linear flow of cells created by complex hydraulics of the flow cytometer followed by illuminating flow path with a LASER beam. This gives very valuable information about cell composition in forward scatter (FSC) and side scatter (SSC). The surface molecules of the cells can further be stained with various florescent dyes which upon excitation with the LASER beam will give the signal that will be detected by the instrument. Flow cytometer is high-throughput equipment and requires careful operation to get valuable information about the samples. In this chapter, we describe how from a bulk cell sample of medulloblastoma cells, cancer stem cells are isolated.

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.

Immunophenotyping of Human Regulatory T Cells

Regulatory T cells, also known as Tregs, play a pivotal role in maintaining homeostasis of the immune system and self-tolerance. Tregs express CD3, CD4, CD25, and FOXP3 but lack CD127. CD4 and CD3 identify helper T lymphocytes, of which Tregs are a subset. CD25 is IL-2Rα, an essential activation marker that is expressed in high levels on Tregs. FOXP3 is the canonical transcription factor, important in the development, maintenance, and identification of Tregs. CD127 is IL-7 receptor, expressed inversely with suppression, and is therefore downregulated on Tregs. Flow cytometry is a powerful tool that is capable of simultaneously measuring Tregs along with several markers associated with subpopulations of Tregs, activation, maturation, proliferation, and surrogates of functional suppression. This chapter describes a multicolor flow cytometry-based approach to measure human Tregs, including details for surface staining, fixation/permeabilization, intracellular/intranuclear staining, acquisition of samples on a flow cytometer, plus analysis and interpretation of resulting FCS files.

In Vitro Assessment of the Antioxidant Properties of Aqueous Byproduct Extracts of Vitis vinifera

Aqueous extracts were obtained at low temperature with the Naviglio technology from grapevine stalks (Merlot), marc (Merlot and Cabernet Sauvignon) and leaves (Merlot) as typical byproducts of winemaking industry, and their properties were evaluated cytofluorometrically on human dermal fibroblasts. Leaf extracts had the greatest total phenolic ((47.6±3.5) mg/g) and proanthocyanidin ((24.2±0.1) mg/g) contents compared to the others. The preliminary colorimetric MTT (3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide) assay individuated two consecutive non-toxic volume fractions of each extract (from 0.8 to 12.8%) that were adopted for three cytofluorometric tests. The first cell membrane test did not evidence any harmful effects against plasma membranes at the two non-toxic volume fractions. The second mitochondrial membrane test showed a decreased (p<0.01) percentage of cells ((15.7±8.3) vs (32.5±1.3) %) with active polarized mitochondrial membranes at the higher non-cytotoxic volume fractions of extracts from Cabernet Sauvignon marc in response to 4.5 mM H₂O₂, and from Merlot stalks (p<0.05) at 1.5 mM H₂O₂ ((49.3±6.1) vs (64.6±2.4) %) and without H₂O₂ ((89.7±2.4) vs (96.9±1.8) %), compared to the controls submitted to the same H₂O₂ concentration. Conversely, mitochondrial activity of leaf extracts significantly (p<0.05) increased ((96.3±1.8) and (96.4±1.4) %) after treatment with 0.5 mM H₂O₂ at both non-cytotoxic volume fractions compared to control ((88.2±1.1) %). Finally, as evidenced by the third oxidative status test, stalk extracts did not evidence relevant effects on the cellular oxidative state, while the extracts of marc and leaves demonstrated significantly medium (p<0.05) to highly (p<0.001) positive effects following exposure to H₂O₂ ranging from 0.5 to 4.5 mM, compared to controls.

Sizing biological cells using a microfluidic acoustic flow cytometer

We describe a new technique that combines ultrasound and microfluidics to rapidly size and count cells in a high-throughput and label-free fashion. Using 3D hydrodynamic flow focusing, cells are streamed single file through an ultrasound beam where ultrasound scattering events from each individual cell are acquired. The ultrasound operates at a center frequency of 375 MHz with a wavelength of 4 μm; when the ultrasound wavelength is similar to the size of a scatterer, the power spectra of the backscattered ultrasound waves have distinct features at specific frequencies that are directly related to the cell size. Our approach determines cell sizes through a comparison of these distinct spectral features with established theoretical models. We perform an analysis of two types of cells: acute myeloid leukemia cells, where 2,390 measurements resulted in a mean size of 10.0 ± 1.7 μm, and HT29 colorectal cancer cells, where 1,955 measurements resulted in a mean size of 15.0 ± 2.3 μm. These results and histogram distributions agree very well with those measured from a Coulter Counter Multisizer 4. Our technique is the first to combine ultrasound and microfluidics to determine the cell size with the potential for multi-parameter cellular characterization using fluorescence, light scattering and quantitative photoacoustic techniques.