Identification of live cells for flow cytometric analysis of lymphoid subset proliferation in low viability populations

Isolation of B-cells using Miltenyi MACS bead isolation kits

This article describes the procedures used to isolate pure B-cell populations from whole blood using various Miltenyi magnetic-activated cell sorting (MACS) bead Isolation kits. Such populations are vital for studies investigating the functional capacity of B-cells, as the presence of other cell types may have indirect effects on B-cell function through cell-cell interactions or by secretion of several soluble molecules. B-cells can be isolated by two main approaches: 1) Negative selection—in which B-cells remain “untouched” in their native state; this is advantageous as it is likely that B-cells remain functionally unaltered by this process. 2) Positive selection–in which B-cells are labelled and actively removed from the sample. We used three Negative B-cell isolation kits as well as the Positive B-cell isolation kit from Miltenyi and compared the purity of each of the resulting B-cells fractions. Contamination of isolated B-cell fractions with platelets was the conclusive finding for all of the isolation techniques tested. These results illustrate the inefficiency of current available MACS B-cell isolation kits to produce pure B-cell populations, from which concrete findings can be made. As such we suggest cell sorting as the preferred method for isolating pure B-cells to be used for downstream functional assays.

Highlighting a need to distinguish cell cycle signatures from cellular responses to chemotherapeutics in SR-FTIR spectroscopy

Previous research has seen difficulties in establishing clear discrimination by principal component analysis (PCA) between drug-treated cells analysed by single point SR-FTIR spectroscopy, relative to multisampling cell monolayers by conventional FTIR. It is suggested that the issue arises due to signal mixing between cellular-response signatures and cell cycle phase contributions in individual cells. Consequently, chemometric distinction of cell spectra treated with multiple drugs is difficult even with supervised methods. In an effort to separate cell cycle chemistry from cellular response chemistry in the spectra, renal carcinoma cells were stained with propidium iodide and fluorescent-activated cell sorted (FACS) after exposure to a number of chemotherapeutic compounds; 5-fluorouracil (5FU) and a set of novel gold-based experimental compounds. The cell spectra were analysed separately by PCA in G(1), S or G(2)/M phase. The mode of action of established drug 5FU, known to disrupt S phase, was confirmed by FACS analysis. The chemical signature of 5FU-treated cells discriminated against both the control and gold-compound (KF0101)-treated cell spectra, suggesting a different mode of action due to a difference in cellular response.

Five-color flow cytometric analysis of swine lymphocytes for detection of proliferation, apoptosis, viability, and phenotype

BACKGROUND

The objective of this study was to develop a method to simultaneously examine phenotype, proliferation, apoptosis, and death of antigen-stimulated porcine lymphocytes.

METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated from pigs vaccinated with a Brachyspira hyodysenteriae bacterin.

RESULTS

Once isolated, PBMCs were stained with the fluorescent membrane intercalating dye, PKH67, and cultured with or without B. hyodysenteriae whole-cell sonicate antigen. Serial samples of nonstimulated and B. hyodysenteriae-stimulated PBMCs were harvested for flow cytometric analysis. Fluorochrome excitation was performed with spatially separated air-cooled argon and red helium neon laser beams. Five-color analysis included signal detection of PKH67 (proliferation), phycoerythrin (cell surface antigen), Texas Red phycoerythrin tandem (cell surface antigen), allophycocyanin (annexin V), and 7-amino-actinomysin D (7AAD; viability). For analysis, gates were set on live (annexin V(-), 7AAD(-)), intact apoptotic (annexin V(+), 7AAD(dim)), and live plus intact apoptotic (annexin V(+/-), 7AAD(dim/-)) cells, and the phenotypes of PBMCs within these populations were determined during the course of the in vitro response. Dead cells (i.e., 7AAD(bright)) were excluded from the analysis.

CONCLUSION

Application of this method for the determination of porcine lymphocyte subset proliferation is presented.

Simultaneous flow cytometric measurement of viability and lymphocyte subset proliferation

Combined analysis of DNA content and immunofluorescence on single cells by flow cytometry provides information on the proliferative response of cellular sub-populations in mixed cell preparations. However, the presence of considerable numbers of dead (nonviable) cells impairs accurate flow cytometric data analysis, mainly, because dead cells can bind antibodies non-specifically and show alterations in their DNA staining profiles. We developed a rapid method for identification of dead cells by fluorescence in cell preparations that are stained simultaneously for two-color immunofluorescence and DNA content. Cells are stained with 7-aminoactinomycin D (7-AAD) for dead cell discrimination and with fluorescein-isothiocyanate (FITC) and phycoerythrin (PE)-labeled monoclonal antibodies (mAb) for cell surface immunofluorescence. Diffusion of 7-AAD from stained, dead cells into unstained, live cells after cell permeabilization is blocked by the addition of its non-fluorescent analogue actinomycin D (AD). DNA is stained with red-excitable TO-PRO-3 iodide (TP3) which has an emission spectrum that can be effectively separated from the emissions of FITC, PE, and 7-AAD. TP3 staining is performed in the presence of ribonuclease A (RNAse) in phosphate-citrate buffer containing saponin (PCBS) at low pH. FITC fluorescence is sensitive to acid pH; therefore, PCBS is replaced after DNA staining with 1x PBS at pH 7.2 containing saponin to permit accurate detection of FITC immunofluorescence on the flow cytometer. We apply this method to the analysis of differential proliferation of lymphocyte subsets in cultures of human peripheral blood mononuclear cells (PBMC) with low viability.

Optimization of cell permeabilization for multiparametric flow cytometric analysis with lectin staining

BACKGROUND

This study was undertaken in mice to develop a reproducible procedure of cell permeabilization, allowing intracellular protein staining by immunofluorescence (i.e., Bcl-2) without losing surface labeling especially for lectins (i.e., B220 and peanut agglutinin [PNA]). This article reports results obtained with different permeabilization protocols.

METHODS

Lymphoid cells were extracted and prepared from Peyer's patches and spleen. After surface labeling using anti-B220-Cy-chrome and PNA-biotin/streptavidin-phycoerythrin, we comparatively tested three permeabilization protocols: saponin 0.3%, methanol 70%, and the commercial kit Dako Intrastain. Final Bcl-2 staining was performed and cells were analyzed by flow cytometry.

RESULTS

With 0.3% saponin as the permeabilization reagent, a significant loss of lectin labeling was observed when comparing mono PNA and triple (i.e. , B220-PNA-Bcl-2) staining (74.8% and 22.5% positive cells, respectively). Quality of PNA staining was conserved with Intrastain when comparing multiparametric versus monoparametric stainings (82. 4% of positive cells versus 78.3%, respectively). Intrastain preserved scatter characteristics (69.9% of total cells in the lymphocyte gate with Intrastain versus 13.7% with saponin 0.3% and 20.9% with methanol 70%). This protocol has been used for a preliminary multiparametric analysis in order to quantify Bcl-2 expression in PNA/B220-positive cells.

CONCLUSION

This protocol may be useful to assess simultaneously lectin cell surface labeling and intracellular target staining.

Discrimination of damaged/dead cells by propidium iodide uptake in immunofluorescently labeled populations analyzed by phase-sensitive flow cytometry

We report a flow cytometric fluorescence lifetime-based method to discriminate damaged/dead from viable cells in immunofluorescently labeled populations using propidium iodide as a dye-exclusion viability probe. Fluorescence signals from propidium iodide and the anti-thymus cell-surface immunofluorescence marker fluorochromes, phycoerythrin and phycoerythrin/Texas Red (tandem conjugate), which have overlapping emission spectra with propidium iodide, are resolved based on differences in their fluorescence emission lifetimes using phase-sensitive detection. Mouse thymus cell samples were first labeled separately with anti-Thy 1.2 antibody directly conjugated to phycoerythrin and to phycoerythrin/Texas Red and propidium iodide. Labeled cells were then analyzed to determine the lifetimes of the immunofluorescence markers and propidium iodide. Based on these results, rat and mouse thymocytes labeled with anti-Thy 1.1 conjugated to phycoerythrin and anti-Thy 1.2 conjugated to phycoerythrin/Texas Red, respectively, were suspended in phosphate buffered saline containing propidium iodide, and were analyzed as they passed through a flow chamber and crossed a high-frequency, intensity-modulated (sinusoidal) laser excitation beam. The resulting immunofluorescence and propidium iodide signals were resolved based on differences in fluorescence lifetimes expressed as phase shifts using phase-sensitive detection and displayed as frequency distribution histograms and bivariate contour diagrams. This technology provides a new method to resolve immunofluorescence and propidium iodide signals from overlapping fluorescence emission spectra and a flow cytometric lifetime-based technique to quantify damaged/dead cells in immunofluorescence studies.

A novel fluorescein-histamine reagent to quantitate histamine receptor expression on leucocytes

The expression of histamine receptors on the surface of rat lymph node cells was studied using a reagent made by directly coupling fluorescein isothiocyanate (FITC) to histamine. This approach contrasts with the use of previous reagents, made by coupling histamine and fluorescein separately to a protein carrier, which bind non-specifically to cells and cause staining unrelated to histamine receptor expression. The new reagent was used, in combination with a panel of monoclonal antibodies, for the dual staining of rat lymph node cells for two-colour flow cytometric analysis to investigate the distribution of histamine receptors on different leucocyte subsets. The majority of cells were stained by the FITC-histamine reagent and these constituted two distinct populations, those with the properties of small lymphocytes and a second population which included macrophages. Inhibition studies with the drugs mepyramine and cimetidine, which are antagonists of H1 and H2 receptors, respectively, showed that most lymphocytes possess H1 receptors while the macrophages have H2 receptors. It seems that macrophages have a higher number of histamine receptors than the majority of lymphocytes, but that they are of lower affinity.

Preservation of B-cell-associated surface antigens by chemical fixation

Usual methods of chemical fixation preclude examination of cells with most monoclonal antibodies due to alteration or destruction of the surface antigen itself. A method of chemical stabilization and preservation of human B-cell-associated surface antigens is described which facilitates retrospective flow cytometric analysis. This method involves pretreatment of the cells with protease enzyme inhibitors, followed by chemical cross-linking of surface proteins with 2% formalin, and finally blockade of non-specific reactive groups with excess glycine. Once prepared, the expression of pertinent cellular antigens is stable on the cell surface for as long as 4 years. Such methodology could conceivably be used for preparation of cells for longitudinal quality control of monoclonal antibodies or archival storage of patient specimens for retrospective flow cytometric analysis.

Single UV excitation of Hoechst 33342 and ethidium bromide for simultaneous cell cycle analysis and viability determinations on in vitro cultures of murine B lymphocytes

Assessment of DNA content by flow cytometry has largely depended on staining techniques which do not permit exclusion of dead cells from the data set. During studies of B cell activation in vitro, the large number of nonviable cells greatly affects the cell cycle distribution and thus the accurate evaluation of proliferation flow cytometry. This report describes the development of two dual staining techniques which use Hoechst 33342 and ethidium bromide excited by a single UV source to eliminate dead cells from the DNA histogram of the viable cells in murine B cell cultures. Hoechst 33342 and 0.62 micrograms/ml of ethidium bromide permit the evaluation of cell cycle distributions on the viable cells with a ratio gate. The combination of Hoechst 33342 and 6.2 micrograms/ml ethidium bromide results in the resolution of the two populations due to fluorescence energy transfer with a single PMT. Using this technique we demonstrated the simultaneous determination of DNA and RNA content on viable cells using only two PMTs. Both these techniques can be performed on either a laser or an arc lamp flow cytometer where CVs of less than 7% and as low as 3.2% are normally achieved. Determination of the S phase using these techniques produces a high correlation with DNA synthesis determined by radiolabeled precursor determination. These techniques permit the use of flow cytometry to determine proliferation during B cell activation.

Metal-induced alteration of the cell membrane/cytoplasm complex studied by flow cytometry and detergent lysis

Flow cytometric analysis of the cell cycle is most effectively accomplished with membrane-/cytoplasm-free ("clean") nuclei. Non-ionic detergents (e.g. NP40 or Triton X-100) commonly are employed to solubilize cell membranes/cytoplasm to produce "clean" nuclei. Treatment of murine erythroleukemic cells (MELC) with tri-n-butyltin methoxide, cadmium acetate, zinc sulfate, or lead acetate alters the properties of the cell membrane/cytoplasm complex making it resistant to NP40 dissolution. On a molar basis, the organotin compound was more effective in inducing resistance to detergent-mediated dissolution than the inorganic metal compounds. Resistance to NP40-mediated dissolution was manifested as an increase in the flow cytometric parameters 90 degrees scatter and fluorescein isothiocyanate (FITC) fluorescence and was confirmed by light microscopy.

The use of dansyl lysine to assess heat damage and thermotolerance of normal tissues

The fraction of cells excluding the fluorescent dye dansyl lysine has previously been shown to correlate well with heat-induced cell killing in a variety of mammalian cell lines and in murine tumors in vivo. Here we evaluate the usefulness of dansyl lysine as a probe for assessment of thermal damage and for measuring the kinetics of thermotolerance development and decay in murine normal tissues. Skin cells were heated in vivo with an initial treatment of 44 degrees C for 20 min by local radiofrequency. Bone marrow cells were heated at 42.5 degrees C for 20 min by whole body water bath immersion. Cell suspensions were prepared, heated in vitro for various lengths of time at 44 degrees C (skin) or 43 degrees C (bone marrow), and scored for the fraction of dansyl lysine-excluding cells. Skin and bone marrow cells expressed maximum thermotolerance by 8 and 6 hr, respectively and returned to normal heat sensitivity by 48 and 146 hr, respectively. The assay was not useful with skeletal muscle and liver, as we were not successful in obtaining viable, dansyl lysine-excluding cells from these tissues. Also, in our hands red blood cells, normal human leukocytes, mouse spleen and thymus cells all failed to stain dansyl lysine even after extreme heating. Dansyl lysine staining, particularly when combined with flow cytometry analysis, has been shown to be a useful method for assessing thermal damage and thermotolerance relatively rapidly in all tumor systems tested to date, and, as shown here, may possess utility in measuring similar endpoints for certain nonclonogenic normal tissues.

Fixation and long-term storage of human lymphocytes for surface marker analysis by flow cytometry

A method to preserve stained human lymphocytes for subsequent cell surface analysis by flow cytometry (FCM) is described. Cells stained with fluorescein isothiocyanate (FITC) and phycoerythrin (PE)-conjugated monoclonal antibodies and then fixed in 1% paraformaldehyde, followed by extensive washing and resuspension in 1% BSA medium, could be stored at 4 degrees C for at least 2 weeks prior to FCM analysis without significant alteration in the light scatter or fluorescence properties of the cells. Furthermore, the method was also suitable for analyzing lymphocytes that express T-cell activation markers in certain disease conditions. In addition, we have identified monoclonal antibody combinations that discriminate different lymphocyte subsets that are satisfactory for multiparameter analysis after 2 weeks of storage. This method should prove useful for enumerating lymphocyte subsets in field study sites remote from flow cytometry laboratories.

Utility of formaldehyde fixation for flow cytometry and inactivation of the AIDS associated retrovirus

To maximize safety in the setting of an increasing number of requests for flow cytometric analysis of specimens potentially contaminated with the AIDS retrovirus, we evaluated some commonly used fixatives for their ability to inactivate the infectious potential of the virus. We found that both formaldehyde (0.37% v/v) and paraformaldehyde (0.5% w/v) completely inactivated the infectious activity of both free and cell-associated lymphadenopathy associated virus (LAV), the etiologic agent for the acquired immunodeficiency syndrome (AIDS). Based on encouraging preliminary results we formally evaluated the effect of formaldehyde fixation on flow cytometric parameters. In addition to inactivating LAV, 0.37% formaldehyde in phosphate buffered saline preserved light scatter and fluorescence properties of cells stained with fluorescein isothiocyanate (FITC) and beta-phycoerythrin (PE) conjugated monoclonal antibodies. These findings suggest that formalin fixation may be useful for laboratories performing flow cytometric analysis of specimens potentially contaminated with the AIDS virus.