The ischemic time window of ectopic endometrial tissue crucially determines its ability to develop into endometriotic lesions

Endometriosis develop from shed endometrial fragments via retrograde menstruation. This affects the survival, proliferation and vascularization of the tissue and its final ability to form endometriotic lesions. Within this study, uterine tissue samples from donor mice were precultivated for 24 h or 72 h to simulate avascular periods. Their morphology, microvessel density, apoptotic activity and expression of angiogenesis-related proteins were analyzed in vitro. The formation of endometriotic lesions in vivo was assessed after transplantation of precultivated uterine tissue samples to the abdominal wall and dorsal skinfold chambers by means of high-resolution ultrasound, intravital fluorescence microscopy, histology and immunohistochemistry. In vitro, 72-h-precultivated uterine tissue samples exhibit extensive areas of tissue necrosis and high numbers of apoptotic cells as well as a significantly reduced cell and microvessel density. These samples failed to develop into endometriotic lesions. In contrast, the 24-h-precultivated samples showed, that their early vascularization and growth in vivo was improved when compared to controls. This indicates that avascular periods have a strong impact on the survival of ectopic endometrial tissue and the chance for the development of endometriosis.

Acoustofluidic separation of cells and particles

Acoustofluidics, the integration of acoustics and microfluidics, is a rapidly growing research field that is addressing challenges in biology, medicine, chemistry, engineering, and physics. In particular, acoustofluidic separation of biological targets from complex fluids has proven to be a powerful tool due to the label-free, biocompatible, and contact-free nature of the technology. By carefully designing and tuning the applied acoustic field, cells and other bioparticles can be isolated with high yield, purity, and biocompatibility. Recent advances in acoustofluidics, such as the development of automated, point-of-care devices for isolating sub-micron bioparticles, address many of the limitations of conventional separation tools. More importantly, advances in the research lab are quickly being adopted to solve clinical problems. In this review article, we discuss working principles of acoustofluidic separation, compare different approaches of acoustofluidic separation, and provide a synopsis of how it is being applied in both traditional applications, such as blood component separation, cell washing, and fluorescence activated cell sorting, as well as emerging applications, including circulating tumor cell and exosome isolation.

Measuring DNA content in live cells by fluorescence microscopy

Background

Live-cell fluorescence microscopy (LCFM) is a powerful tool used to investigate cellular dynamics in real time. However, the capacity to simultaneously measure DNA content in cells being tracked over time remains challenged by dye-associated toxicities. The ability to measure DNA content in single cells by means of LCFM would allow cellular stage and ploidy to be coupled with a variety of imaging directed analyses. Here we describe a widely applicable nontoxic approach for measuring DNA content in live cells by fluorescence microscopy. This method relies on introducing a live-cell membrane-permeant DNA fluorophore, such as Hoechst 33342, into the culture medium of cells at the end of any live-cell imaging experiment and measuring each cell’s integrated nuclear fluorescence to quantify DNA content. Importantly, our method overcomes the toxicity and induction of DNA damage typically caused by live-cell dyes through strategic timing of adding the dye to the cultures; allowing unperturbed cells to be imaged for any interval of time before quantifying their DNA content. We assess the performance of our method empirically and discuss adaptations that can be implemented using this technique.

Results

Presented in conjunction with cells expressing a histone 2B-GFP fusion protein (H2B-GFP), we demonstrated how this method enabled chromosomal segregation errors to be tracked in cells as they progressed through cellular division that were later identified as either diploid or polyploid. We also describe and provide an automated Matlab-derived algorithm that measures the integrated nuclear fluorescence in each cell and subsequently plots these measurements into a cell cycle histogram for each frame imaged. The algorithm’s accurate assessment of DNA content was validated by parallel flow cytometric studies.

Conclusions

This method allows the examination of single-cell dynamics to be correlated with cellular stage and ploidy in a high-throughput fashion. The approach is suitable for any standard epifluorescence microscope equipped with a stable illumination source and either a stage-top incubator or an enclosed live-cell incubation chamber. Collectively, we anticipate that this method will allow high-resolution microscopic analysis of cellular processes involving cell cycle progression, such as checkpoint activation, DNA replication, and cellular division.

Electronic supplementary material

The online version of this article (10.1186/s13008-018-0039-z) contains supplementary material, which is available to authorized users.

Contributions to the dynamics of cervix remodeling prior to term and preterm birth

Major clinical challenges for obstetricians and neonatologists result from early cervix remodeling and preterm birth. Complications related to cervix remodeling or delivery account for significant morbidity in newborns and peripartum mothers. Understanding morphology and structure of the cervix in pregnant women is limited mostly to the period soon before and after birth. However, evidence in rodent models supports a working hypothesis that a convergence of factors promotes a physiological inflammatory process that degrades the extracellular collagen matrix and enhances biomechanical distensibility of the cervix well before the uterus develops the contractile capabilities for labor. Contributing factors to this remodeling process include innervation, mechanical stretch, hypoxia, and proinflammatory mediators. Importantly, the softening and shift to ripening occurs while progesterone is near peak concentrations in circulation across species. Since progesterone is required to maintain pregnancy, the premise of this review is that loss of responsiveness to progesterone constitutes a common final mechanism for remodeling the mammalian cervix in preparation for birth at term. Various inputs are suggested to promote signaling between stromal cells and resident macrophages to drive proinflammatory processes that advance the soft cervix into ripening. With infection, pathophysiological processes may prematurely drive components of this remodeling mechanism and lead to preterm birth. Identification of critical molecules and pathways from studies in various rodent models hold promise for novel endpoints to assess risk and provide innovative approaches to treat preterm birth or promote the progress of ripening at term.

Mitochondrial staining allows robust elimination of apoptotic and damaged cells during cell sorting

High-speed fluorescence-activated cell sorting is relevant for a plethora of applications, such as PCR-based techniques, microarrays, cloning, and propagation of selected cell populations. We suggest a simple cell-sorting technique to eliminate early and late apoptotic and necrotic cells, with good signal-to-noise ratio and a high-purity yield. The mitochondrial potential dye, TMRE (tetramethylrhodamine ethyl ester perchlorate), was used to separate viable and non-apoptotic cells from the cell sorting samples. TMRE staining is reversible and does not affect cell proliferation and viability. Sorted TMRE(+) cells contained a negligible percentage of apoptotic and damaged cells and had a higher proliferative potential as compared with their counterpart cells, sorted on the basis of staining with DNA viability dye. This novel sorting technique using TMRE does not interfere with subsequent functional assays and is a method of choice for the enrichment of functionally active, unbiased cell populations.

Standardization of a method to detect bovine sperm-bound antisperm antibodies by flow cytometry

The objectives were to standardize some methodological and analytical aspects of a direct technique to detect sperm-bound antisperm antibodies (ASAs) in bovine semen using flow cytometry, including the effects of prefixation of sperm membranes with formalin buffer solution and inclusion of dead cells in the analysis. Fourteen Angus bulls, including ASA-positive (experimentally induced ASAs) and 10 reproductively normal ASA-negative bulls, were used. Fixation of sperm membranes had no significant effect on the percentage of IgG- or IgA-bound spermatozoa detected by flow cytometry. However, including dead cells in the analysis increased the percentage of IgG-bound spermatozoa in fixed (live and dead 18.6 ± 9.7% and live 1.3 ± 0.5%; median ± SEM) and nonfixed samples (live and dead 18.8 ± 9.2%, live 1.5 ± 0.6%; P = 0.0029), as well as IgA-bound spermatozoa in fixed (live and dead 16.3 ± 6.4%, live 0.3 ± 0.5%) and nonfixed samples (live and dead 21.4 ± 4.6%, live 1.0 ± 0.5%; P = 0.0041) in semen from ASA-negative bulls. Intrasample, intra-assay, and interassay coefficients of variation (CV) were 0.8%, 4.6%, and 5.3%, respectively, for determination of sperm-bound IgG, and were 2.8%, 8.4%, and 40.3% for determination of sperm-bound IgA. Despite the high interassay CV for IgA determination, all ASA-positive bulls consistently had high percentages of IgA-bound spermatozoa. Flow cytometry correctly identified ASA-positive bulls. Confocal laser microscopy confirmed binding of ASAs to sperm heads and cytoplasmic droplets, and less frequently to midpieces and principal piece. In conclusion, although fixation was not necessary, dead cells should be excluded from the analysis, because ejaculates with a large proportion of dead cells can yield false-positive results. Flow cytometry was accurate and reliable for detection of sperm-bound IgG and IgA and discrimination between ASA-positive and ASA-negative bulls.

Amine-reactive dyes for dead cell discrimination in fixed samples

Amine-reactive dyes, also known as LIVE/DEAD fixable dead cell stains, are a class of viability dyes suitable for identifying dead cells in samples that will be fixed. These dyes cross the cell membranes of dead cells, and react with free amines in the cytoplasm. Live cells exclude these dyes because their cell membranes are intact, and free dye is washed away after staining. Notably, the reaction is irreversible; therefore, when cells are fixed and permeabilized (as with intracellular staining procedures), the bound dye remains associated with the dead cells (unlike other viability dyes). Since amine-reactive dyes are fluorescent when excited by lasers, dead cells can be identified by flow cytometry. This unit describes procedures, troubleshooting, and outcomes for using the two most commonly used amine-reactive dyes, ViViD and Aqua Blue.

Improved survival in rhesus macaques immunized with modified vaccinia virus Ankara recombinants expressing simian immunodeficiency virus envelope correlates with reduction in memory CD4+ T-cell loss and higher titers of neutralizing antibody

Previous studies demonstrated that immunization of macaques with simian immunodeficiency virus (SIV) Gag-Pol and Env recombinants of the attenuated poxvirus modified vaccinia virus Ankara (MVA) provided protection from high viremia and AIDS following challenge with a pathogenic strain of SIV. Although all animals became infected, plasma viremia was significantly reduced in animals that received the MVA-SIV recombinant vaccines compared with animals that received nonrecombinant MVA. Most importantly, the reduction in viremia resulted in a significant increase in median and cumulative survival. Continued analysis of these animals over the subsequent 9 years has shown that they maintain a survival advantage, although all but two of the macaques have progressed to AIDS. Importantly, improved survival correlated with preservation of memory CD4(+) T cells in the peripheral blood. The greatest survival advantage was observed in macaques immunized with regimens containing SIV Env, and the titer of neutralizing antibodies to the challenge virus prior to or shortly following challenge correlated with preservation of CD4(+) T cells. These data are consistent with a role for neutralizing antibodies in nonsterilizing protection from high viremia and associated memory CD4(+) T-cell loss.

Acute leukemia immunohistochemistry: a systematic diagnostic approach

CONTEXT

The diagnosis and classification of leukemia is becoming increasingly complex. Current classification schemes incorporate morphologic features, immunophenotype, molecular genetics, and clinical data to specifically categorize leukemias into various subtypes. Although sophisticated methodologies are frequently used to detect characteristic features conferring diagnostic, prognostic, or therapeutic implications, a thorough microscopic examination remains essential to the pathologic evaluation. Detailed blast immunophenotyping can be performed with lineage- and maturation-specific markers. Although no one marker is pathognomonic for one malignancy, a well-chosen panel of antibodies can efficiently aid the diagnosis and classification of acute leukemias.

OBJECTIVE

To review important developments from recent and historical literature. General immunohistochemical staining patterns of the most commonly encountered lymphoid and myeloid leukemias are emphasized. The goal is to discuss the immunostaining of acute leukemias when flow cytometry and genetic studies are not available.

DATA SOURCES

A comprehensive review was performed of the relevant literature indexed in PubMed (National Library of Medicine) and referenced medical texts. Additional references were identified in the reviewed manuscripts.

CONCLUSIONS

Immunophenotyping of blasts using an immunohistochemical approach to lymphoid and myeloid malignancies is presented. Initial and subsequent additional antibody panels are suggested to confirm or exclude each possibility in the differential diagnosis and a general strategy for diagnostic evaluation is discussed. Although the use of immunohistochemistry alone is limited and evaluation by flow cytometry and genetic studies is highly recommended, unavoidable situations requiring analysis of formalin-fixed tissue specimens arise. When performed in an optimized laboratory and combined with a careful morphologic examination, the immunohistochemical approach represents a useful laboratory tool for classifying various leukemias.

The histone deacetylase inhibitor ITF2357 selectively targets cells bearing mutated JAK2(V617F)

We investigated the activity of ITF2357, a novel histone deacetylase inhibitor (HDACi) with antitumor activity, on cells carrying the JAK2(V617F) mutation obtained from polycythemia vera (PV) and essential thrombocythemia (ET) patients as well as the HEL cell line. The clonogenic activity of JAK2(V617F) mutated cells was inhibited by low concentrations of ITF2357 (IC(50) 0.001-0.01 microM), 100- to 250-fold lower than required to inhibit growth of normal or tumor cells lacking this mutation. Under these conditions, ITF2357 allowed a seven fold increase in the outgrowth of unmutated over mutated colonies. By western blotting we showed that in HEL cells, ITF2357 led to the disappearance of total and phosphorylated JAK2(V617F) as well as pSTAT5 and pSTAT3, but it did not affect the wild-type JAK2 or STAT proteins in the control K562 cell line. By real-time PCR, we showed that, upon exposure to ITF2357, JAK2(V617F) mRNA was not modified in granulocytes from PV patients while the expression of the PRV-1 gene, a known target of JAK2, was rapidly downmodulated. Altogether, the data presented suggest that ITF2357 inhibits proliferation of cells bearing the JAK2(V617F) mutation through a specific downmodulation of the JAK2(V617F) protein and inhibition of its downstream signaling.

Live-cell assay for detection of apoptosis by dual-laser flow cytometry using Hoechst 33342 and 7-amino-actinomycin D

This protocol describes a rapid and simple method for the identification of apoptotic cells. Owing to changes in membrane permeability, early apoptotic cells show an increased uptake of the vital DNA dye Hoechst 33342 (HO342) compared with live cells. The nonvital DNA dye 7-amino-actinomycin D (7-AAD) is added to distinguish late apoptotic or necrotic cells that have lost membrane integrity from early apoptotic cells that still have intact membranes as assayed by dye exclusion. The method is suitable to be combined with cell surface staining using Abs of interest labeled with fluorochromes that are compatible with HO342 and 7-AAD emissions. Surface antigen staining is carried out according to standard methods before staining for apoptosis. The basic assay can be completed in 30 min, and extra time is needed for cell surface antigen staining.

Requirement of aggregation propensity of Alzheimer amyloid peptides for neuronal cell surface binding

Background

Aggregation of the amyloid peptides, Aβ40 and Aβ42, is known to be involved in the pathology of Alzheimer's disease (AD). Here we investigate the relationship between peptide aggregation and cell surface binding of three forms of Aβ (Aβ40, Aβ42, and an Aβ mutant).

Results

Using confocal microscopy and flow cytometry with fluorescently labelled Aβ, we demonstrate a correlation between the aggregation propensity of the Alzheimer amyloid peptides and their neuronal cell surface association. We find that the highly aggregation prone Aβ42 associates with the surface of neuronal cells within one hour, while the less aggregation prone Aβ40 associates over 24 hours. We show that a double mutation in Aβ42 that reduces its aggregation propensity also reduces its association with the cell surface. Furthermore, we find that a cell line that is resistant to Aβ cytotoxicity, the non-neuronal human lymphoma cell line U937, does not bind either Aβ40 or Aβ42.

Conclusion

Taken together, our findings reveal that amyloid peptide aggregation propensity is an essential determinant of neuronal cell surface association. We anticipate that our approach, involving Aβ imaging in live cells, will be highly useful for evaluating the efficacy of therapeutic drugs that prevent toxic Aβ association with neuronal cells.

Accurate assessment of cell count and viability with a flow cytometer

BACKGROUND

In this study we developed a method to measure cell concentration and viability in specimens received in flow cytometry and cytogenetics laboratories.

METHODS

Specimens are stained with a vital fluorescent dye, SYTO13, the cell impermeant viability dye, 7-AAD, and a leukocyte marker, CD45. After the addition of an internal calibrator microsphere, FLOW-COUNT, the flow cytometer is capable of measuring the viability of nucleated cells, giving a general assessment of leukocyte populations and measuring their concentration.

RESULTS

An accurate assessment of specimen quality is an important parameter when performing flow cytometric and cytogenetic leukemia/lymphoma assessment. High quality specimen is desired to avoid the pitfalls of non-specific staining and limited cellularity/viability.

CONCLUSIONS

Use of a cell count and viability measurement prior to leukemia and lymphoma assessment by flow cytometry and cytogenetics helps to increase the rate of successful immunophenotypic and cytogenetic analysis.

Amine reactive dyes: An effective tool to discriminate live and dead cells in polychromatic flow cytometry

Membrane-damaged cells caused by either mechanical trauma or through normal biological processes can produce artifacts in immunophenotyping analysis by flow cytometry. Dead cells can nonspecifically bind monoclonal antibody conjugates, potentially leading to erroneous conclusions, particularly when cell frequencies are low. To date, DNA intercalating dyes (Ethidium monoazaide (EMA), Propidium Iodide, 7AAD, etc.) or Annexin V have been commonly used to exclude dead cells; however, each suffer from technical problems. The first issue with such dyes is the dependence on a consistent dead cell source for fluorescence compensation. Another major issue is the stability of the staining; except for EMA, fixation and permeablization used for intracellular staining procedures can cause loss of fluorescence. EMA requires a UV exposure to covalently bond to DNA; while this dye is effective and is not affected by intracellular treatments it is weakly fluorescent. Here we report on the optimization of a new class of viability dyes, the amine reactive viability dyes (ViD) as a dead cell exclusion marker. The inclusion of ViD into the staining panel was found to be simple, reproducible and can have a significant benefit on the accuracy of identifying appropriate cell populations. We show the fluorescence of cells stained with these dyes correlates with traditional dead cell discriminating markers, even after fixation and permeabilization. Amine reactive viability dyes are a powerful tool for fluorescence immunophenotyping experiments.

Early apoptosis largely accounts for functional impairment of CD34+ cells in frozen-thawed stem cell grafts

Quality assessment of stem cell grafts is usually performed by flow cytometric CD34(+) enumeration or assessment of clonogenic output of fresh material. Previously, we identified the occurrence of early apoptosis, not detectable with the permeability marker 7-amino actinomycin D (7-AAD), in purified frozen-thawed CD34(+) cells, using the vital stain Syto16. Syto(high)/7-AAD(-) cells were defined as viable, Syto16(low)/7-AAD(-) cells as early apoptotic and Syto16(low)/7-AAD(+) as dead. This was confirmed in a subsequent study using frozen-thawed transplants of lymphoma patients. In the present study on grafts from multiple myeloma and lymphoma patients, we investigated the functional consequences of the early apoptotic process. The mean Syto16-defined viability was 41 and 42%, respectively, for both graft groups, compared to 78% and 72%, respectively, using 7-AAD only. The established early apoptosis marker annexin V missed roughly 50% of the early apoptosis detected with Syto16. In contrast, viability of CD34(+) cells in nonmanipulated whole blood transplants from a matched group of lymphoma patients, after 72 h of storage at 4 degrees C, was more than 90%, even with the Syto16 assay. CFU recovery (median 26-33%) after cryopreservation matched CD34(+) recovery after Syto16, but not 7-AAD correction. In contrast, colony-forming unit (CFU) recovery in the whole blood transplant was close to 100%. Furthermore, early apoptotic CD34(+) cells had lost migratory ability toward stromal cell derived factor-1alpha (SDF-1alpha). The establishment of a Syto16(high)/7-AAD(-) proportion of CD34(+) cells offers a new approach for a more correct determination of the number of viable nonapoptotic CD34(+) cells in stem cell grafts. Further development of this assay should allow its incorporation into the routine CD34(+) assessment of post-thawed samples in clinical flow cytometry laboratories.

Extensive early apoptosis in frozen-thawed CD34-positive stem cells decreases threshold doses for haematological recovery after autologous peripheral blood progenitor cell transplantation

Stem cell doses necessary for engraftment after myelo-ablative therapy as defined for fresh transplants vary largely. Loss of CD34+ cell quality after cryopreservation might contribute to this variation. With a new early apoptosis assay including the vital stain Syto16, together with the permeability marker 7-AAD, CD34+ cell viability in leucapheresis samples of 49 lymphoma patients receiving a BEAM regimen was analysed. After freeze-thawing large numbers of non-viable, early apoptotic cells appeared, leading to only 42% viability compared to 72% using 7-AAD only. Based on this Syto16 staining in the frozen-thawed grafts, threshold numbers for adequate haematological recovery of 2.8-3.0 x 10(6) CD34+ cells/kg body weight determined for fresh grafts, now decreased to 1.2-1.3 x 10(6) CD34+ cells/kg. In whole blood transplantation of lymphoma patients (n = 45) receiving a BEAM-like regimen, low doses of CD34+ cells were sufficient for recovery (0.3-0.4 x 10(6)CD34+ cells/kg). In contrast to freeze-thawing of leucapheresis material, a high viability of CD34+ cells was preserved during storage for 3 days at 4 degrees C, leaving threshold doses for recovery unchanged. In conclusion, the Syto16 assay reveals the presence of many more non-functional stem cells in frozen-thawed transplants than presumed thus far. This led to a factor 2.3-fold adjustment downward of viable CD34+ threshold doses for haematological recovery.

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.

Intracellular hepatitis B virus nucleocapsids survive cytotoxic T-lymphocyte-induced apoptosis

Following antigen recognition, hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTL) induce a necroinflammatory liver disease in HBV-transgenic mice. An early event in this process is CTL-dependent activation of apoptosis in a small fraction of HBV-positive hepatocytes. Here we show that cytoplasmic HBV nucleocapsids and their cargo of replicative DNA intermediates survive CTL-induced apoptosis of hepatocytes in vitro. These results suggest that destruction of infected cells per se is not sufficient to destroy the replicating HBV genome in infected tissue and that other events in addition to this process are required for viral clearance to occur.

Detection of dead cells and measurement of cell killing by flow cytometry

A flow cytometer can quickly perform numerous quantitative, sensitive measurements on each individual cell within a large, heterogeneous population. The modern commercially available analytical instruments, which can be found in most hospitals, pathology laboratories, and cell biology research laboratories in the industrially developed countries, can now routinely measure fluorescence simultaneously at four different wavelengths, in addition to light scatter in two directions, at rates of thousands of cells per second. Thus, flow cytometry provides a powerful and versatile approach to the measurement of cell death and cell killing. However, it is important to stress that the biological nature of the phenomenon under investigation will determine which assay is appropriate, and at what stage in the process of cell killing it should be applied. This consideration is particularly important in the study of drug- or cell-mediated cytotoxicity.

Measurement of lymphocyte subset proliferation by three-color immunofluorescence and DNA flow cytometry

We developed a method for simultaneous flow cytometric analysis of three-color immunofluorescence and DNA content. We show here that staining with 7-amino-actinomycin D (7-AAD) at 10 microg/ml using a phosphate-citrate buffer at low pH containing saponin for cell membrane permeabilization yields good resolution DNA histograms with low coefficients of variation. Furthermore, light scatter properties of cells are preserved after permeabilization; this permits gating on cell populations that differ in scatter signals on the flow cytometer. Because of the low pH of the phosphate-citrate staining buffer, Alexa488, a pH-independent green-fluorescent fluorochrome is used instead of fluorescein-isothiocyanate (FITC) for cell surface staining in combination with phycoerythrin (PE) and with allophycocyanin (APC) which are both pH insensitive. Removal of 7-AAD after staining and replacing it with non-fluorescent actinomycin D (AD) retains DNA staining and allows detection of Alexa488, PE and APC cell surface immunofluorescence without interference from fluorescent 7-AAD in solution for clear identification of cell subpopulations even after prolonged stimulation in culture. Thus, using a four-color benchtop flow cytometer, measurement of Alexa488, PE and APC three-color immunofluorescence can be combined with 7-AAD DNA content analysis. Furthermore, we demonstrate that sample storage overnight without fixation for later analysis on the flow cytometer is possible without compromising results. Application of the method to the assessment of the differential proliferative responses of lymphocyte subsets of human peripheral blood mononuclear cells (PBMC) that were costimulated with CD3 and with CD28.2 is presented.

Detection of cell cycle subcompartments by flow cytometric estimation of DNA-RNA content in combination with dual-color immunofluorescence

BACKGROUND

Correlated flow cytometric measurements of phenotype and DNA-RNA content offer detailed information on cell cycle status of subpopulations in heterogeneous cell preparations in response to stimulation. We have developed a method for flow cytometric analysis of DNA-RNA content that has been optimized for simultaneous measurement of dual-color immunofluorescence.

METHODS

Nucleic acid staining was performed at low pH in the presence of saponin. DNA was stained with 7-aminoactinomycin D (7-AAD) and RNA with pyronin Y(G) (PY); both dyes were used at low concentrations, and 7-AAD was exchanged with nonfluorescent actinomycin D after DNA staining to minimize fluorochrome-fluorochrome interactions. For cell surface antigen staining, allophycocyanin was combined with pH-independent Alexa488 instead of fluorescein-isothiocyanate (FITC) because FITC is pH sensitive.

RESULTS

This method identified cell cycle subcompartments in CEM cells comparable to published results on cell lines using other dyes and staining methods. Measurement of DNA-RNA content in CD8 lymphocyte subsets of human peripheral blood mononuclear cells costimulated with CD3/CD28.2 showed that, after 48 h of stimulation, 80% of CD8(+) T cells were in the proliferative state, whereas 86% of CD8(+) non-T cells remained in G(0).

CONCLUSIONS

This technique permits the clear identification of cellular subpopulations by phenotype and assessment of their cell cycle status.

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.