Flow cytometric measurement of [Ca2+]i and pHi in conjugated natural killer cells and K562 target cells during the cytotoxic process

Measurement of intracellular ions by flow cytometry

Using flow cytometry, single-cell measurements of calcium can be made on isolated populations identified by one or more phenotypic characteristics. Most earlier techniques for measuring cellular activation parameters determined the mean value for a population of cells, which did not permit optimal resolution of the responses. The flow cytometer is particularly useful for this purpose because it can measure ion concentrations in large numbers of single cells and thereby allows ion concentration to be correlated with other parameters such as immunophenotype and cell cycle stage. A limitation of flow cytometry, however, is that it does not permit resolution of certain complex kinetic responses such as cellular oscillatory responses. This unit describes the preparation of cells, including labeling with antibodies and with calcium probes, and discusses the principles of data analysis and interpretation.

Measurement of intracellular calcium ions by flow cytometry

Using flow cytometry, single-cell measurements of calcium can be made on isolated populations identified by one or more phenotypic characteristics. This unit describes the preparation of cells, including labeling with antibodies and with calcium probes, and discusses the principles of data analysis and interpretation.

Tracing apoptosis and stimulation in individual cells by fluorescence intensity and anisotropy decay

Presented is the use of fluorescence lifetime (FLT), anisotropy decay, and associated parameters as differential indicators of cellular activity. A specially designed combination of a frequency mode based time resolved microscope and a picoliter well-per-cell array have been used to perform temporal measurements in individual cells under various biological conditions. Two biological models have been examined: mitogenic activation of peripheral blood mononuclear cells (PBMC) and induction of programmed cell death (apoptosis) in Jurkat T cells (JTC). The FLT of fluorescein stained PBMC was found to increase from 4+/-0.02 to 4.5+/-0.025 ns due to mitogenic activation, whereas during apoptosis in fluorescein stained JTC, the FLT remained constant. Notably, the rotational correlation times changed in both models: decreased in PBMC from 2.5+/-0.08 to 2+/-0.1 ns, and increased in JTC from 2.1+/-0.07 to 3.3+/-0.09 ns. FLT and rotational correlation time were used to calculate the steady state fluorescence anisotropy (FA) which was compared to directly measured FA values. The present study suggests that in addition to bioindication, the said parameters can provide valuable information about cellular mechanisms that may involve complex molecular diffusion dynamics, as well as information about structural changes that a cellular fluorophore undergoes in the course of cell activation.

Measurement of intracellular ions by flow cytometry

The recent development of a number of new fluorescent probes makes it possible to measure the concentrations of various intracellular free ions in single living cells. Among these ions are calcium, magnesium, sodium, potassium, and hydrogen (pH). This unit describes flow cytometric protocols using the dyes Indo-1 AM, Fluo-3, and Fura Red AM to measure intracellular calcium concentration. Support protocols detail the use of calcium buffers to calibrate a flow cytometric calcium assay, and methods to facilitate dye loading; an alternate protocol describes the use of a spectrofluorimeter to measure intracellular calcium for those investigators without access to a flow cytometer.

Flow cytometry for natural killer T cells: multi-parameter methods for multifunctional cells

Valpha24-Jalpha18 invariant natural killer T cells (iNKT) are an evolutionary conserved sub-lineage of T cells with effector-memory phenotype that often express an NK cell surface antigen CD161 and is characterized by reactivity to self-glycolipids and alpha-galactosylceramide (alphaGalCer) that are presented by monomorphic HLA class-I-like molecule CD1d. Upon antigen recognition, iNKT cells can rapidly produce multiple cytokines and chemokines and regulate development of Th-2 and Th-1 immune responses. Potential importance of iNKT cells has been demonstrated in several animal models of infection diseases, autoimmunity, and cancer. Multi-parameter flow cytometry has been the main tool to study human and murine iNKT cells. Analysis of human iNKT cells is particularly demanding since their frequency among peripheral blood T cells is relatively low ranging from less than 0.01% to 1%, with a mean of about 0.1%. Herein, we discuss flow cytometry applications that are utilized for iNKT cell identification and enumeration, subset characterization, detection of intracellular cytokines, quantitative analysis of multiple secreted molecules, cell-mediated cytotoxicity, and migration.

Determination of individual cell Michaelis-Menten constants

BACKGROUND

A novel methodology for the measurement and analysis of apparent K(M) (Michaelis-Menten constant) and V(MAX) values of individual cells is suggested. It is based on a mathematical model that considers substrate influx into the cell, its intracellular enzymatic hydrolysis, and the product efflux. The mathematical formulation was approximated linearly in order to analyze intracellular substrate conversion characteristics via Michaelis-Menten theory.

METHODS

Utilizing static cytometry, the time dependence of the fluorescence intensity [FI(t)] emitted from prelocalized and defined FDA stained cells was recorded. This required frequent periodical measurements of the same cells, which are sequentially exposed to various fluorogenic substrate concentrations.

RESULTS

Model simulations correlated with experimental results. Differences in distributions of individual K(M) and V(MAX) values of cells incubated with and without PHA were evident. Average K(M) and V(MAX) values of PHA-stimulated cells increased by 99% and 540%, respectively.

CONCLUSIONS

This study may provide a tool for assessing intracellular enzymatic activity in individual intact cells under defined physiologic conditions. This may open new vistas in various areas, giving answers to critical questions arising in the field of cell and developmental biology, immunology, oncology, and pharmacology.

A novel technique for the fluorometric assessment of T lymphocyte antigen specific lysis

The 51Cr release assay has traditionally been used to investigate effector cell cytotoxic function against labeled targets, but this method has inherent problems that include hazards associated with radioactivity, cell labeling and high spontaneous release. Here we describe a novel flow cytometric assay which addresses and improves upon the problems currently encountered with the 51Cr release assay. The fluorometric assessment of T lymphocyte antigen specific lysis (FATAL) assay employs dual staining (PKH-26 and CFSE) to identify and evaluate the target population. We found that the PKH-26/CFSE combination efficiently labeled target cells. Evaluation of the spontaneous leakage from dye labeled target cells was forty fold lower than the spontaneous leakage seen with the 51Cr release assay. The FATAL assay permitted a more accurate assessment of the effector: target ratio, and detected low levels of cytotoxic T lymphocyte (CTL) mediated lysis. There was a strong correlation between the 51Cr release and FATAL assays, when performed in parallel with identical effector and target cells (r(2)=0.998, P=<0.0001). This novel method of detecting cytolysis represents a qualitative and quantitative improvement over standard 51Cr release analysis. The FATAL assay will be of value to further investigate mechanisms of cytolysis by effector cell populations.

Changes in intracellular calcium concentration and pH of target cells during the cytotoxic process: a quantitative study at the single cell level

This study reports on the changes in intracellular calcium concentration ([Ca2+]in) and intracellular pH ([pH]in) that occur in K562 target cells during interaction with human Natural Killer (NK) cells. The data were obtained using a quantitative fluorescence microscope and fluorescent ratio probes specific for [Ca2+]in (Fura-2-AM) and [pH]in (BCECF-AM). Results demonstrate that two types of target cell response to the attack by an NK cell can be distinguished. The target cell either dies immediately, due to the complete breakdown of the membrane impermeability, or the initial membrane damage (i.e., increased membrane permeability) is repaired and the cell "escapes" immediate death. During both responses an increase of [Ca2+]in takes place in the target cells. In the cells that die immediately, however, [Ca2+]in reaches higher levels (approximately 1,400 nM) than in the cells that restore the initial damage (approximately 700 nM). Changes in target cell [pH]in are also detected during both responses. The direction of the change (acidification or alkalinization) as well as the level of the change depend on extracellular pH ([pH]ex). Also, [pH]in remains changed during the time the cells were followed (10 min). The programming time (i.e., the time from the initiation of the cytotoxic process to the time that a change in the physiological parameter was detected) of the killing process that leads to an immediate target cell death appears to be shortest at [pH]ex 7.3-7.6 (approximately 3 min).

Flow cytometric measurement of NK cell immunoconjugates by pulse width processing

Pulse width analysis, in flow cytometry, has been widely used for optimal cell size resolution in cell kinetics analysis. Pulses, generated by scattered light or fluorescence of cells, are electronically analyzed for their height and width. The information generated from these two properties of the pulses is utilized to distinguish signals from single cells vs. signals from cell clumps or aggregates. Pulse width, unlike pulse height, is more sensitive to differences in cell diameter, and therefore can discriminate very small differences in it, which pulse height cannot. We have exploited this property of pulse widths to measure immunoconjugates between NK cells and their targets. Discrimination of the free target cells from the conjugated ones is possible by the pulse widths of only light scatter signals, both forward and/or orthogonal. This resolution was not obtained if pulse height of the same signals was visualized. Using this resolution it was possible to distinguish single cells from the aggregates between target and effector cells. We propose that this is a better method for distinguishing conjugates than the method in which prior vital staining of cells is used.

Flow cytometric determination of intracellular calcium changes in human peripheral blood mononuclear cells during conjugation to tumour cell lines

Using a flow cytometric assay, conjugate formation between human peripheral blood mononuclear cells (PBMC) and three different human tumour cell lines has been analysed. Changes in the intracellular calcium levels of PBMC were monitored using the calcium sensitive dye Fluo-3. Target cell populations were distinguished by forward scatter or following loading with the fluorescent dye, SNARF-1. Intracellular calcium was expressed as a ratio of fluorescence of conjugated to unconjugated PBMC and followed for ten minutes after initiation of conjugation. The results demonstrate an apparent increase in intracellular calcium in PBMC conjugated to the NK-sensitive cell line K562, and that the kinetics and magnitude of this response varied considerably between individuals. Tumour cells which were resistant to lysis (as determined in a 4 h chromium release assay) were also capable of eliciting a calcium response from PBMC. Although the induction of a rise in intracellular calcium was therefore not correlated with cytotoxicity, it was greater in IL-2-activated PBMC upon exposure to the same target cell lines as PBMC.

Preliminary characterization of lymphoid hybridoma cell lines derived from the pregnant mouse uterus

Seven independent cell lines were derived from the fusion of migratory cells recovered from explant cultures of metrial glands to SP 2/0, a non-Ig secreting B cell myeloma. The migrating cells came from a pool of metrial glands from day 6-8 pregnant random bred CD1 mice and were assumed to be cells early in the differentiation pathway to granulated metrial gland (GMG) cells. The fused cells were cloned twice at the limiting dilution. Hybridization was confirmed by quantitation of cellular DNA using propidium iodide staining and by karyotyping. Electron microscopy revealed that each of the hybrid cell lines was composed of cells which were lymphoid in appearance, but lacked the granules found in mature GMG cells. The surface phenotype of all lines is CD45+, LGL-1-, asialo GM-1-, IgG-, IgM-, CD3- and CD25- (p55 of IL-2 receptor). Although the hybridomas lack those phenotypic markers which were used to show that GMG cells are related to the natural killer (NK) cell lineage (ie LGL-1, asialo GM-1), they do express the pan-leukocyte marker CD45 as well as the lytic protein, perforin, at levels intermediate to those of SP 2/0 cells and GMG cells. In addition, the hybridomas were observed to preferentially bind the NK target cell YAC and to be capable of lytic activity at temperatures below 30 degrees C. Because these hybridomas may represent fusion to an early progenitor cell of the NK/GMG cell lineage, their continued characterization is of merit.

Spectra of fluorescent dyes used in flow cytometry

Flow cytometry uses a relatively small set of dyes for immunochemistry and nucleic acid detection, most of which have been known and used reliably in flow cytometry for several years. These can usually be combined to make simultaneous two-color measurements of multiple cell-surface antigens and nucleic acid content. Because of the overlap of dye spectra and difficulties in finding dyes with substantial Stokes shifts that can be excited by the argon laser, simultaneous three-color or more detection can be more difficult. A basic knowledge of the factors that go into producing the fluorescent signal, including the spectra of dyes and their overlap, is necessary in planning multicolor experiments. By contrast, there have been a number of new fluorescent probes developed for detecting ions, membrane potential, metabolism, organelles, and other properties of living cells as well as for determining cell viability, proliferation, and cell tracking. So far most of these physiological probes are being used only for fundamental research rather than for cell classification. However, as research activity expands in this area, its diagnostic potential is likely to be increasingly appreciated.

A flow cytometric study of the membrane potential of natural killer and K562 cells during the cytotoxic process

This study demonstrates that it is possible to investigate the membrane potential of interacting cells during the cytotoxic process using flow cytometry. Changes in the membrane potential of NK and K562 cells, involved in a cell-mediated cytotoxic process, were studied by standard and slit-scan flow cytometry, using the membrane potential sensitive fluorescent probe DiBAC4(3). The NK cells were labeled with a membrane marker (TR-18 or DiI) prior to incubation with K562 cells and the conjugates that were formed could be identified on the basis of the membrane marker fluorescence and light scattering signals. With a slit-scan technique we measured the membrane potential of each cell in a conjugate separately. The results show that depolarization of the K562 cell occurs as a consequence of the cytotoxic activity of the NK cell. This depolarization appears to be an early sign of cell damage because the cell membrane still remains impermeable to propidium iodide. Our data also indicate that depolarization of the NK cell occurs as a result of its cytotoxic activity.