Flow cytometric enumeration of DNA-stained oceanic planktonic protists

The aim of this study was to test the practicality of enumeratingfixed, DNA-stained heterotrophic protists (H) and phototrophicprotists (P) in contrasting regions of the Atlantic Ocean. Oceanicprotists were enumerated using a standard flow cytometer (FACSort,BD) at an enhanced flow rate of up to 1.0 mL min^–1 toincrease numbers of counted cells. The enumeration error ofprotists decreased hyperbolically from 30–40 to < 5%corresponding to the number (<100 to > 2000) of enumeratedcells. H and P were discriminated using the extra red chlorophyll-derivedplastidic fluorescence of the latter. The relationship betweencounts of stained and unstained fixed and unfixed P was statisticallyclose to 1:1, confirming the accuracy of stained protist countingby flow cytometry and adequate discrimination of P from H cells.The estimated average abundance of H in the surface mixed layerof the southern and northern oligotrophic gyres was remarkablysimilar, with 400 ± 140 and 450 ± 60 cells mL^–1,respectively, adding further evidence to the suggestion thatthese regions are in steady state. In agreement with earlierstudies in more productive aquatic environments, a significantcorrelation (correlation coefficient 0.84, P < 0.0001) wasfound between the H and the total bacterioplankton numbers,with an average ratio of 1300 prokaryotes to 1 H cell, suggestinga relatively constant trophic interaction between these twogroups. This study demonstrates that flow cytometric enumerationof protists is 100 times faster compared with microscopy and,thus, represents a major improvement for quantifying protistsin ocean waters, including oligotrophic gyres.     

Flow cytometric method for enumeration and classification of reactive immature granulocyte populations

We developed a flow cytometric method for the enumeration and classification of nonmalignant immature granulocytes (IG). In this study, IG are defined as most immature (IG stage 1: promyelocytes and myelocytes) and as more mature (IG stage 2: metamyelocytes). Blood specimens from 46 patients with documented infectious or inflammatory disease and known presence of IG (by routine manual microscopy) were analyzed. For a reference manual differential count, we used a 400 white blood cell (WBC) differential and separated granulocytes into promyelocytes and myelocytes combined, metamyelocytes, and included band cells in the mature, segmented neutrophil population. The flow cytometric method is based on three-color staining of whole, anticoagulated blood with CD45-PerCP, CD16-FITC, and CD11b-PE-labeled monoclonal antibodies and a three-step gating procedure. The flow cytometric results were confirmed by cell sorting and microscopic evaluation of the sorted cells. A total of 10,000 events, excluding debris, were recorded per specimen and IG stage 1 (CD16-/CD11b-), IG stage 2 (CD16-/CD11b+), and mature neutrophils (CD16+/CD11b+) were categorized. Regression and correlation between flow cytometric IG and the manual differential showed y = 1.34x + 0.95, r(2) = 0.86 for IG stages 1 and 2 combined versus promyelocytes, myelocytes, and metamyelocytes. For IG stage 1 versus microscopic counts of promyelocytes and myelocytes, the results were y = 1.53x + 1.24, r(2) = 0.76; for IG stage 2 versus manual metamyelocyte count, y = 0.77x + 0.21, r(2) = 0.58. Reproducibility of the flow cytometric method showed a coefficient of variation (CV) of 6.8% for all IG combined compared with a CV of 50.2% for manual differential IG count (based on a routine 100 WBC count). Samples were found stable at least 12 h at 25 degrees C and at least 48 h at 4 degrees C for flow cytometry. After staining and lysing, the sample was stable for at least 120 min at room temperature. We analyzed samples from patients with myelodysplastic and myeloproliferative disease separately. We found that CD16- mature neutrophils falsely elevated the flow cytometric IG count. Similar results were obtained in blood from patients treated with granulocyte-colony stimulating factor (G-CSF). Although this restricts the use of the method somewhat, we believe that this flow cytometric method is useful for enumerating reactive IG, as well as for evaluating automated methods for IG identification by hematology analyzers.     

Flow cytometric enumeration and immunophenotyping of hematopoietic stem and progenitor cells

Flow cytometric enumeration of CD34+ hematopoietic stem and progenitor cells (HPC) is widely used for evaluation of graft adequacy of peripheral blood stem cell grafts, and is also useful in planning the apheresis sessions necessary to obtain these grafts. The state-of-the-art method to enumerate CD34+ cells makes use of a multiparameter definition of HPC based on their light scatter characteristics and dim expression of CD45, and the use of counting beads to derive the concentration of CD34+ cells directly from the flow cytometric assessment. This method can be extended with a viability stain and additional markers for further immunological characterization of CD34+ cells, and has been successfully implemented in multicenter trials. Thus, the lower threshold of a safe HPC graft in terms of short- and long-term hematopoiesis may be more accurately defined.     

Flow cytometric evaluation of anti-herpes drugs

A rapid means of screening drugs for toxicity and anti-herpes simplex virus activity was developed based on the flow cytometric detection of HSV induced changes in cellular DNA content. Subconfluent monolayers of human diploid fibroblasts (HEL 299) were assayed for DNA content with propidium iodide 24 h after infection with HSV-1 (multiplicity of infection 1-10) and treatment with the drug to be tested. Infection was detected by a broadening of the normal diploid and tetraploid peaks and presence of greater than 4-n DNA staining. Inhibition of viral DNA synthesis and maintenance of the normal growth pattern of control cells was indication of antiviral activity. Toxicity of the compound was indicated by the loss of S phase and tetraploid cell populations. Using this assay, we evaluated the activities of one experimental and two established antiviral agents.     

Flow cytometric evaluation of cell cycle characteristics during in vitro differentiation of chick embryo chondrocytes

The cell cycle kinetic characteristics of chick endochondral chondrocytes differentiating in vitro were studied by flow cytometry. In addition, the synthesis of type I and type X collagens of the same cells was evaluated by immunoprecipitation. Dedifferentiated cells, derived from chick embryo tibiae and grown attached to a substratum, were characterized by type I collagen synthesis, a high growth fraction (GF = 0.94), minimal cell loss factor (phi = 0.02), and a total cell cycle time of the proliferating cells of about 17 h (tG1 = 8 h, tS = 5 h, and tG2 + M = 4 h). Transfer of dedifferentiated cells to suspension culture on agarose-coated dishes induced differentiation to hypertrophic chondrocytes. These were characterized by type X collagen synthesis, a low growth fraction (GF = 0.52), maximal cell loss factor (phi = 1.0), and a total cell cycle time of the proliferating cells of about 73 h (tG1 = 53 h, tS = 12 h, and tG2 + M = 8 h). The transition from dedifferentiated chondrocytes to hypertrophic chondrocytes was accompanied by large increases of the duration of all the cell cycle phases and of the number of quiescent and degenerating cells. Associated with these alterations in cell cycle kinetics was a switch from type I to type X collagen synthesis. Further preliminary data suggest that the population of differentiating chondrocytes (a state between dedifferentiated and hypertrophic chondrocytes) comprises a heterogeneous population of fast and slow growing cells.     

Flow cytometric evaluation of leukocyte function in rat whole blood

The aim of this study was to establish a standard flow cytometric method to measure the phagocytic function of and intracellular hydrogen peroxide (H2O2) production by rat leukocytes. Thirty-six adult, male Sprague-Dawley rats were included in this study. Whole-blood specimens from the inferior vena cava were collected in a heparinized tube and ethylenediaminetetraacetic acid (EDTA) anticoagulated tube. The phagocytic function of and intracellular H2O2 generation by leukocytes were measured with FACS Vantage trade mark flow cytometer (Becton Dickinson, San Jose, CA), using fluorescent microspheres and dihydrorhodamine-123 as probes, respectively. Several conditions were optimized in this study, including anticoagulants (heparin and EDTA), fluorescent probes (0.75- and 1.72-microm-diameter microspheres), incubation time, and concentration of the chemicals used in the experiment. Neutrophils, monocytes, and lymphocytes could be clearly defined and separated in whole blood by flow cytometry and tested for phagocytosis and intracellular H2O2 generation without the need for further purification and handling of the cells. Intracellular H2O2 production by and phagocytic function of neutrophils and monocytes were inhibited in EDTA-anticoagulated blood compared with heparin- anticoagulated blood (P < 0.01). Neutrophils showed similar phagocytic function to 0.75- and 1.72-microm microspheres, but monocytes showed weak phagocytic activity to 1.72-microm beads compared with 0.75-microm beads (P < 0.01). In conclusion, a flow cytometric method to measure the phagocytic function of and intracellular H2O2 production by rat leukocytes has been developed. Quantitative flow cytometric analysis of rat leukocyte function is convenient and feasible and provides a reliable and rapid assay to assess phagocytosis and intracellular H2O2 production by rat neutrophils and monocytes.     

Flow cytometric enumeration of absolute lymphocyte number in peripheral blood using two parameters of light scatter

A method was developed to measure the absolute lymphocyte count (ALC) of whole blood using the Spectrum III automated flow cytometer. Ninety-nine samples of human peripheral blood were analysed on the Spectrum and the Coulter Counter S Plus II, to allow for comparison of the two machines. Regression analysis was used to test the extent of agreement between the sets of measurements on the two machines. The results demonstrated that the slope of the regression line was not significantly different from one, indicating a high level of correlation between Spectrum and Coulter ALC's. However, the mean difference between Coulter and Spectrum ALC's was not equal to zero, with the Spectrum giving counts approximately 10% lower than those of the Coulter machine. This is attributed to the different ways by which the two machines define a lymphocyte, the Spectrum III by two parameters of light scatter and the Coulter S Plus II by the single parameter of cell volume.     

Flow cytometric identification and enumeration of photosynthetic sulfur bacteria and potential for ecophysiological studies at the single-cell level

We show the potential of flow cytometry as a fast tool for population identification and enumeration of photosynthetic sulfur bacteria. Purple (PSB) and green sulfur bacteria (GSB) oxidize hydrogen sulfide to elemental sulfur that can act as storage compound to be further oxidized to sulfate generating the reducing power required for growth. Both groups have different elemental sulfur allocation strategies: whereas PSB store elemental sulfur as intracellular inclusions, GSB allocate sulfur globules externally. We used well-characterized laboratory strains and complex natural photosynthetic populations developing in a sharply stratified meromictic lake to show that PSB and GSB could be detected, differentiated and enumerated in unstained samples using a blue laser-based flow cytometer. Variations in cell-specific pigment content and the dynamics of sulfur accumulation, both intra- and extracellularly, were also detected in flow cytometric plots as sulfur accumulation changed the light scatter characteristics of the cells. These data were used to show the potential for studies on the metabolic status and the rate of activity at the single-cell level. Flow cytometric identification and enumeration resulted in faster and more precise analyses than previous approaches, and may open the door to more complex ecophysiological experiments with photosynthetic sulfur bacteria in mixed cultures and natural environments.     

Flow cytometric evaluation of sperm parameters in relation to fertility potential

Most laboratory methods used to evaluate semen quality have not correlated highly with fertilizing capacity. The discovery of a variety of fluorochromes and compounds conjugated to fluorescent probes has enabled a more widespread analysis of sperm attributes, and in conjunction with the flow cytometer, permit the evaluation of a large number of spermatozoa. A number of characteristics of sperm integrity, viability and function can be assessed by flow cytometry. The DNA status of spermatozoa has been determined using the metachromatic properties of acridine orange (AO). AO staining, when used in the sperm chromatin structure assay (SCSA), correlates with fertility in a number of species. DNA fragmentation can also be assessed using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, which identifies DNA strand breaks by labeling free 3'-OH termini with modified nucleotides. The status of the sperm acrosome can be determined using fluorescently labeled lectins and LysoTracker Green DND-26, a fluorescent acidotropic probe. Capacitation status has been observed through calcium-mediated changes using chlortetracycline (CTC) or by changes in membrane fluidity monitored by the binding of the fluorescent amphiphilic probe, Merocyanine 540. Fluorescently labeled annexin-V, C6NBD and Ro-09-0198 can also be used to detect changes in membrane phospholipid distribution. Cell viability can be determined using the propensity of propidium iodide (PI), ethidium homodimer-1 (EthD-1) or Yo-Pro-1 to permeate damaged membranes. These are generally more adaptable to clinical flow cytometry than the bisbenzimide membrane impermeable stain, Hoechst 33258, which excites in the ultraviolet range and requires UV laser equipment. Mitochondrial function can be determined using rhodamine 123 (R123) and MitoTracker Green FM (MITO) and 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1). Flow cytometry is a tool that may be used in the future to monitor many new potential markers of sperm function.     

Flow cytometric evaluation of the cytotoxicity of novel antiviral compounds

Two acyclic analogs of bromotubercidin were tested for cytotoxic effects on uninfected cells by monitoring cell growth and measuring cell cycle perturbations using flow cytometry. As reported elsewhere, 5-bromotubercidin analogs in which ribose was replaced by 2-hydroxyethoxymethyl (compound 102) or by 1,3-dihydroxypropoxymethyl (compound 183) were potent inhibitors of human cytomegalovirus (HCMV) replication in vitro (Pudlo et al.: Journal of Medicinal Chemistry 31:2086-2092, 1988). Because these compounds also inhibited the growth of uninfected cells, we performed kinetic studies with an established neoplastic line of human cells (KB) using flow cytometry. Growth of KB cells treated with either compound 102 or 183 were inhibited in a dose-dependent manner. Growth inhibition by compound 183, however, was not fully expressed for at least 24 h. DNA analysis by flow cytometry showed that a 4-h incubation with 10 microM compound 102 caused a decrease of cells in G2/M phase. Cells began to accumulate in early S phase by 12 h of incubation, leading to mid S phase accumulation at 21 h. Compound 183 at 10 microM slightly decreased the number of cells in G2/M phase after a 4-h incubation, and led to accumulation of DNA in S phase after a 12-h incubation. By 24 and 30 h, DNA histograms appeared similar to those of control cells but with a slight accumulation of the population in early S phase. In separate experiments, drugs were removed following a 24-h incubation. After removal of compound 102, KB cell growth resumed with a normal population doubling time. In contrast, the effects of compound 183 were not reversible, suggesting the two compounds acted by different biochemical mechanisms.     

Flow cytometric evaluation of DNA digestion with S1 nuclease

The digestion of DNA with the S1 nuclease has been investigated by flow cytometry on two cultured cell lines and on splenic lymphocytes. The nucleolytic activity of the enzyme has been determined by measuring the decrease in fluorescence intensity of DNA stained with Propidium Iodide (PI). The reaction kinetics could be estimated through the shift of the G1 peak, since the shape of the DNA histograms obtained from cell submitted to S1 digestion did not show any particular variation as compared with the histograms of undigested control cells. DNA digestion was found to be more pronounced when cells were previously damaged with agents known to induce strand breaks, such as gamma-rays or Adriamycin. The assessment of DNA sensitivity to S1 nuclease with flow cytometry may thus provide a fast and reliable procedure for evaluating chromatin structural changes, both in physiological and pathological conditions.     

Flow cytometric evaluation of human neutrophil apoptosis during nitric oxide generation in vitro: the role of exogenous antioxidants

Among numerous inflammatory mediators a nitric oxide molecule is supposed to be important in the modulation of neutrophil survival in vivo and in vitro. The effect of exogenous supply of NO donors such as SNP, SIN-1, and GEA-3162 on the course of human neutrophil apoptosis and the role of extracellular antioxidants in this process was investigated. Isolated from peripheral blood, neutrophils were cultured in the presence or absence of NO donor compounds and antioxidants for 8, 12, and 20 hours. Apoptosis of neutrophils was determined in vitro by flow cytometric analysis of cellular DNA content and Annexin V protein binding to the cell surface. Exposure of human neutrophils to GEA-3162 and SIN-1 significantly accelerates and enhances their apoptosis in vitro in a time-dependent fashion. In the presence of SNP, intensification of apoptosis has not been revealed until 12 hours after the culture. The inhibition of GEA-3162- and SIN-1-mediated neutrophil apoptosis by superoxide dismutase (SOD) but not by catalase (CAT) was observed. Our results show that SOD and CAT can protect neutrophils against NO-donors-induced apoptosis and suggest that the interaction of NO and oxygen metabolites signals may determine the destructive or protective role of NO donor compounds during apoptotic neutrophil death.     

Flow cytometric evaluation of adhesion of Streptococcus pyogenes to epithelial cells

The precise roles of various surface molecules in the attachment of Streptococcus pyogenes to host epithelia are currently unclear. A flow cytometry assay that facilitates the analysis of the kinetics of S. pyogenes adhesion to epithelial cells was developed. Dose- and time-dependent adhesion isotherms with both buccal epithelial cells (BECs) and Hep-2 cells as substrata were obtained. Although binding equilibrium is reached within 2 h on both cell types, saturation of binding sites on BECs is not achieved within a wide range of experimental conditions. This indicates a high degree of non-specific attachment to that cell type. Since no rinsing step is necessary when using flow cytometry to analyze adhesion, low-affinity associations were observable. This was confirmed by determining bacterial desorption rates early and late in the adsorption process. Binding irregularities were also easily detected since the cytometer records and displays data for up to 10,000 epithelial cells per time point. It is proposed to use this methodology to assign roles to particular surface molecules/characteristics during distinct phases of adhesion.     

Flow cytometric applications in cytopathology

Flow cytometric (FCM) methodology represents a powerful analytical tool for screening and detecting abnormal and malignant cells, for subclassifying malignancies beyond conventional morphologic type and grade and for transcending light microscopic features by providing more biologically meaningful information. This paper reviews the historical background leading to the development of the FCM methodology and instrumentation that is presently being used for cytopathologic (and histopathologic) diagnosis, tumor subclassification and identification of aggressive cancers. Emphasis is placed on human carcinomas, with reference to hematologic malignancies when appropriate. Examples of FCM DNA content and cytokinetic techniques are described for the various cytologic sampling methods. The advantages, limitations and future prospects for the application of flow cytometric techniques in cytopathology are discussed.     

Flow cytometric evaluation of lymphocyte subpopulations in BALF of healthy smokers and nonsmokers

The purpose of this work was to evaluate the normal lymphocyte phenotype in the bronchoalveolar lavage fluid (BALF). BAL was carried out in 12 untreated healthy nonsmoking volunteers and in 9 cigarette smokers. For the analysis of lymphocyte subsets by two-color flow cytometry, the monoclonal antibodies used were directed anti: CD3, CD4, CD8, CD16, CD19, D25, CD45, CD56 and anti HLA-DR. An increase in the total number of cells in BALF of smoking persons and increased proportion of macrophages was observed. The percentage of CD8+ lymphocytes was 1.7 times higher, whereas the proportions of CD4+ cells, and a CD4+/CD8+ ratio were lower 1.5 and 2.6 times, respectively, in the BALF of cigarette smoking persons when compared with nonsmoking volunteers. The changes did not depend on the age of the person. In conclusion, we suggest that the decreased CD4/CD8 ratio and the elevated CD8 T cell subset may be regarded as a potential risk factor associated with clinically asymptomatic lung cancer. Moreover, in the interpretation of BALF from patients with pulmonary diseases cell proportions of nonsmoking and of smoking persons should be compared with the respective controls.     

Re-evaluating acridine orange for rapid flow cytometric enumeration of parasitemia in malaria-infected rodents.

Methods facilitating research in malaria are of pivotal relevance. Flow cytometry offers the possibility of rapid enumeration of parasitemia. It relies on staining the parasite DNA to distinguish between infected and non-infected red blood cell (RBC) populations. Unfortunately, in rodents abundant reticulocyte RNA interferes with the application of the method. This results in time-consuming sample preparation protocols that offer no clear advantage over microscopic counting. We re-evaluated the use of the DNA/RNA discriminating vital fluorochrome acridine orange (AO) for rapid flow cytometric enumeration of parasitemia in rodents. Whole blood from rodents infected with Plasmodium berghei and Plasmodium yoelii was stained with AO and analyzed by flow cytometer. A newly developed two-channel (FL1/FL3) detection method was compared with conventional one-channel (FL1) detection and microscopic counting. The new AO two-channel detection method clearly discriminated between infected and non-infected RBC populations. It showed to be linear above parasitemias of 0.3%. Sample processing time amounted to approximately 5 min. It is shown that AO can be used for rapid, precise, and accurate enumeration of parasitemia in rodents. Due to its ease of handling the method might find widespread application in malaria research.     

Flow cytometric evaluation of cell dispersion from human head and neck tumors

The preparation of single-cell suspensions from 25 human head and neck tumors is described. Dispersal was performed overnight at 4 degrees C under slight agitation of the tissue suspensions using various combinations of enzymes and additives. The cell suspensions were examined for number of cells released, viability, amount of debris, and DNA distribution by means of flow cytometry (FCM). It was shown that both trypsin/dithioerythritol (TD) and collagenase/D Nase (CDse) were of value in dispersing single cells from tumor tissue. In contrast to CDse, incubation with TD appeared to be cytolytic to normal lymphocytes. In a number of cases, DNA-FCM revealed ploidy abnormalities in a TD-suspension, which were not discernible in the concurrent CDse-suspension. Cell culture of primary cell suspensions corroborated the reliability of the DNA-FCM measurements. Pretreatment with CDse improved tumor disaggregation by TD and indicated a different dispersal capacity. Addition of Ca2+ and Mg2+ ions to the dispersal mixtures and preincubation of tumor slices in complete medium for 1 day before initiation of cell dispersion influenced favorably the quality of the cell suspension.     

Flow cytometric analysis of microorganisms

The application of flow cytometry to microorganisms is as old as the technique itself, but it has historically been underexploited for microbial applications. This is now being reversed and microbiologists are ideally placed to benefit from recent technological advances. While earlier papers demonstrated the use of flow cytometry for studies of viability and taxonomy, recent developments in bioinformatics and reporter gene technologies are leading to novel applications in microbiology. Variants of green fluorescent protein have been used for the study of conditional microbial gene regulation in medically important host-pathogen interactions and fluorescence-activated cell sorting is being applied to the isolation of novel mutants in directed evolution studies. This paper reviews the reasons for the delay in the application of flow cytometry to microbial problems, the range of applications, and their limitations and considers the progress made in developing new strategies for use in microbiological investigations.