Sequential paraformaldehyde and methanol fixation for simultaneous flow cytometric analysis of DNA, cell surface proteins, and intracellular proteins

Analysis of the multiparametric cell cycle data

This chapter was originally written in 2011. The idea was to give some history of cell cycle analysis before and after flow cytometry became widely accessible; provide references to educational material for single parameter DNA content analysis, introduce and discuss multiparameter cell cycle analysis in a methodological style, and in a casual style, discuss aspects of the work over the last 40years that we have given thought, performing some experiments, but didn't publish. It feels like there is a linear progression that moves from counting cells for growth curves, to counting labeled mitotic cells by autoradiography, to DNA content analysis, to cell cycle states defined by immunofluorescence plus DNA content analysis, to extraction of cell cycle expression profiles, and finally to probability state modeling, which should be the "right" way to analyze cytometric cell cycle data. This is the sense of this chapter. In 2023, we have updated it, but the exciting, expansive aspects brought about by spectral and mass cytometry are still young and developing, and thus have not been vetted, reviewed, and presented in mature form.

High-throughput RNA sequencing of paraformaldehyde-fixed single cells

Single-cell transcriptomic studies that require intracellular protein staining, rare cell sorting, or inactivation of infectious pathogens are severely limited. This is because current high-throughput single-cell RNA sequencing methods are either incompatible with or necessitate laborious sample preprocessing for paraformaldehyde treatment, a common tissue and cell fixation and preservation technique. Here we present FD-seq (Fixed Droplet RNA sequencing), a high-throughput method for droplet-based RNA sequencing of paraformaldehyde-fixed, permeabilized and sorted single cells. We show that FD-seq preserves the RNA integrity and relative gene expression levels after fixation and permeabilization. Furthermore, FD-seq can detect a higher number of genes and transcripts than methanol fixation. We first apply FD-seq to analyze a rare subpopulation of cells supporting lytic reactivation of the human tumor virus KSHV, and identify TMEM119 as a potential host factor that mediates viral reactivation. Second, we find that infection with the human betacoronavirus OC43 leads to upregulation of pro-inflammatory pathways in cells that are exposed to the virus but fail to express high levels of viral genes. FD-seq thus enables integrating phenotypic with transcriptomic information in rare cell subpopulations, and preserving and inactivating pathogenic samples.

High-throughput RNA sequencing of paraformaldehyde-fixed single cells

Single-cell transcriptomic studies that require intracellular protein staining, rare cell sorting, or inactivation of infectious pathogens are severely limited. This is because current high-throughput single-cell RNA sequencing methods are either incompatible with or necessitate laborious sample preprocessing for paraformaldehyde treatment, a common tissue and cell fixation and preservation technique. Here we present FD-seq (Fixed Droplet RNA sequencing), a high-throughput method for droplet-based RNA sequencing of paraformaldehyde-fixed, permeabilized and sorted single cells. We show that FD-seq preserves the RNA integrity and relative gene expression levels after fixation and permeabilization. Furthermore, FD-seq can detect a higher number of genes and transcripts than methanol fixation. We first apply FD-seq to analyze a rare subpopulation of cells supporting lytic reactivation of the human tumor virus KSHV, and identify TMEM119 as a potential host factor that mediates viral reactivation. Second, we find that infection with the human betacoronavirus OC43 leads to upregulation of pro-inflammatory pathways in cells that are exposed to the virus but fail to express high levels of viral genes. FD-seq thus enables integrating phenotypic with transcriptomic information in rare cell subpopulations, and preserving and inactivating pathogenic samples.

Current high-throughput single-cell transcriptomic methods are incompatible with paraformaldehyde, a common cell fixation technique. Here the authors present FD-seq, a method for droplet-based RNA sequencing of paraformaldehyde-fixed, stained and sorted single cells.

Efficacy of the Antigenicity-Retaining Ability of Fixative Solutions for Liquid-Based Cytology: Immunocytochemistry of Long-Term Storage

INTRODUCTION/OBJECTIVE

Liquid-based cytology (LBC) is advantageous as multiple stained specimens can be prepared and used for additional assays such as immunocytochemical and molecular-pathological investigations. Two types of preservative-fixative solutions (fixatives) are used for nongynecologic specimens used in the BD SurePath-LBC (SP-LBC) method, and their components vary. However, few studies have evaluated the differences in antigen-retaining ability between these fixatives. Therefore, we investigated and compared the antigen-retaining ability of the fixatives in immunocytochemical staining (ICC) under long-term storage conditions.

MATERIALS AND METHODS

Sediments of cultured RAJI cells (derived from Burkitt's lymphoma) were added to each fixative (red and blue) and stored at room temperature for a specified period (1 h; 1 week; and 1, 3, and 6 months). The specimens were then prepared using the SP-LBC method and subjected to ICC. Positivity rate was calculated using the specimens fixed at room temperature for 1 h as a control. Antibodies against Ki67 expressed in the nucleus and against CD20 and leukocyte common antigen (LCA) expressed on the cell membrane were used.

RESULTS

For CD20 and LCA, the positivity rate increased with time in the red fixative compared with that in the control. In the blue fixative, the positivity rate was highest at 1 h and was maintained at a high level throughout the storage period. In contrast, the Ki67 positivity rate was highest at 1 h in both red and blue fixatives and markedly decreased with time. Therefore, although refrigerated (8°C) storage was used, no improvement was noted.

CONCLUSIONS

Long-term storage is possible for cell membrane antigens at room temperature; however, it is unsuitable for intranuclear antigens. Therefore, we conclude that suitable fixative type and storage temperature differ based on antigen location. Further investigation is warranted.

Conformation-specific monoclonal antibodies recognizing the native structure of G protein-coupled receptor (GPCR)

It is quite difficult to generate monoclonal antibodies that recognize the three-dimensional structures of the antigens of interest. To address this limitation, we developed a new hybridoma technology termed "optimized stereospecific targeting (SST)". Here we aimed at generating stereospecific monoclonal antibodies against a G protein-coupled receptor (GPCR). The optimized SST technique enabled the efficient production of conformation-specific monoclonal antibodies against human corticotropin-releasing hormone receptor 1 (huCRHR1). Hybridoma cells secreting stereospecific monoclonal antibodies were selectively cloned by a limiting dilution method and the target monoclonal antibodies were purified by protein A column chromatography. They specifically cross-reacted with native huCRHR1 expressed on the surface of CHO cells, whereas they showed no affinity for MDA-MB-231 cancer cells, which abundantly express EphA2 on the cell surface. Furthermore, immunofluorescence analysis revealed that treatment of huCRHR1-expressing CHO cells with 4% paraformaldehyde led to a decrease in the affinity of purified monoclonal antibodies for intact huCRHR1 on the cell surface. In addition, purified monoclonal antibodies showed no cross-reactivity with huCRHR1 expressed on Sf9 insect cells. These results strongly suggest that monoclonal antibodies generated by the optimized SST technique feature specific binding to the intact form of the target GPCR on mammalian cells.

Application of digital holographic tomography in antitumor effect of cantharides complex on 4T1 breast cancer cells

The study focuses on a methodology providing noninvasive monitoring and evaluation of the antitumor effect of traditional Chinese medicine, cantharides complex (canth), on 4T1 breast tumor cells. Digital holographic tomography (DHT) and developed data post-processing algorithms were used for quantitative estimation of changes in optical and morphological parameters of cells. We calculated and compared data on the refractive index, thickness, and projected area of 4T1 breast tumor cells in control untreated specimens and those treated with doxorubicin hydrochloride (DOX), canth, and their combinations. Post-treatment changes in cellular morphology recorded by DHT demonstrated that the two drugs led to noticeably different morphological changes in cells that can be presumably associated with different pathways of their death, apoptosis, or necrosis. The effect of combined treatment with these two drugs strongly depended on their relative concentrations and could lead to changes characteristic either for DOX or for canth; however, being more profound than those obtained when using each drug solely. The results obtained by DHT are in a good correspondence with commonly used cell viability analysis and immunofluorescent analysis of changes in cellular cytoskeleton.

Fixed single-cell RNA sequencing for understanding virus infection and host response

Single-cell transcriptomic studies that require intracellular protein staining, rare cell sorting, or inactivation of infectious pathogens are severely limited because current high-throughput RNA sequencing methods are incompatible with paraformaldehyde treatment, a common tissue and cell fixation and preservation technique. Here we present FD-seq, a high-throughput method for droplet-based RNA sequencing of paraformaldehyde-fixed, stained and sorted single-cells. We show that FD-seq preserves the mRNA integrity and relative abundances during fixation and subsequent cell retrieval. Furthermore, FD-seq detects a higher number of genes and transcripts than methanol fixation. We applied FD-seq to investigate two important questions in Virology. First, by analyzing a rare population of cells supporting lytic reactivation of the human tumor virus KSHV, we identified TMEM119 as a host factor that mediates viral reactivation. Second, we found that upon infection with the betacoronavirus OC43, which causes the common cold and is a close relative of SARS-CoV-2, pro-inflammatory pathways are primarily upregulated in lowly-infected cells that are exposed to the virus but fail to express high levels of viral genes. FD-seq thus enables integrating phenotypic with transcriptomic information in rare cell populations, and preserving and inactivating pathogenic samples that cannot be handled under regular biosafety measures.

Investigation of the response of tear-film neutrophils to interleukin 8 and their sensitivity to centrifugation, fixation, and incubation

During eye closure, a large number of neutrophils (polymorphonuclear neutrophils, PMNs) invade the ocular surface and are often referred to as tear-film PMNs. While immunophenotyping experiments have been performed on tear-film PMNs, the impact of commonly used experimental procedures on their phenotype as well as their response to interleukin-8 (IL-8), a physiological inflammatory mediator, have not yet been investigated. A gentle eye wash method was used to collect cells at home. In the morning upon awaking, participants washed their eyes with sterile phosphate buffer saline (PBS) and collected the runoff into a sterile polypropylene tube. The cell collection was then delivered to the lab within two hours. The effects of centrifugation, incubation and fixation with paraformaldehyde (PFA) before (pre-fixed staining) or after (post-fixed staining) incubation with antibodies were characterized. Tear-film PMNs as well as blood PMNs (used for comparison) were also stimulated with IL-8. To assess the reproducibility of cell collection and variability in receptor expression over time, participants were also asked to collect cells three times over a period of a month. The change in expression of surface receptors, CD11b, CD16, CD55, CD66b, important inflammatory and activation markers, and CD45 (PAN leukocyte marker) was assessed by flow cytometry. Fixing tear-film PMNs prior to the staining with antibodies resulted in a significant (fivefold or more) reduction in the expression of CD11b, CD16 and CD45 when compared to unfixed samples, while CD16 was the only receptor to undergo significant downregulation upon post-staining fixation. Furthermore, additional centrifugation step prior to antibody incubation as well as long (4 h) incubation at 37 °C resulted in significant reductions in expression of CD11b, CD16 and CD55 when compared to control samples. As opposed to blood PMNs, stimulating tear-film PMNs with IL-8 did not induce any significant changes in expression of CD11b, CD16, CD55 and CD66b. When working with collected tear-film PMNs, our results suggest that any additional centrifugation and incubation step should be avoided, or at least limited, and post fixation staining is recommended in order to preserve cell phenotype and cell integrity of tear film PMNs. Our study also adds further information on the reproducibility of the gentle eye wash as well as the inability of tear-film PMNs to modulate their surface receptors upon stimulation with IL-8. The latter may be due to prior exposure to IL-8, activation in the closed-eye environment, or a reduced ability to respond to inflammatory stimulus. Further mechanistic studies will be needed to gain a better understanding of the tear-film neutrophil phenotype.

Analyzing the scaffold immune microenvironment using flow cytometry: practices, methods and considerations for immune analysis of biomaterials

The immune system has evolved as a powerful tool for our body to combat infections, and is being engineered for new treatments in cancer and autoimmune disease. More recently, the complex role of the immune system is being recognized in tissue repair, regenerative medicine and biomaterial responses. From these combined interests, the field of immunoengineering is rapidly growing. However, bridging immunology with engineering poses numerous challenges including the biological complexity, language of immunology and accurately leveraging the powerful techniques of immunology to new applications. Elucidating the identity and function of immune cell populations responding to engineering systems will be required for continued advancement. Multi-color flow cytometry is a central technique used by immunologists for this purpose that requires careful control of variables, data acquisition, and interpretation. Here, we present methods for multi-color flow cytometry experimental design and analysis focused on characterizing the scaffold immune microenvironment in regenerative medicine research.

An optimized permeabilization step for flow cytometry analysis of nuclear proteins in myeloid differentiation of blood cells into neutrophils

Polymorphonuclear leukocytes (PMNLs) or neutrophils play an important role in the innate immune response. Working with human neutrophils is challenging because these cells are sensitive to changes in the surrounding media and quickly become apoptotic. Meanwhile the experiments with mature neutrophils may be very important for studies of blood function. In this paper we propose an improved technique of flow cytometry nuclear protein analysis with double antibody labeling, which allows direct comparison of protein quantity (overlay histograms) in the primary cells (neutrophils) and progenitor cell lines (line HL-60), to study differentiation process and for other research purposes. We suggest improved technique to analyze and compare nuclear proteins levels in the myeloid differentiation model system (HL-60 cell line) and / or primary human neutrophils. This method was justified with measurement of GFI1 protein expression level, as well-known transcription factor, typical and essential for mature neutrophils. The key protocol features are as follows: •Suggested protocol allows simply, direct and correct visual comparison of flow cytometry data in overlay diagrams for myeloid blood cells on various stages of differentiation.•70% ethanol permeabilization of neutrophils and HL-60 cells results in lower background fluorescence and better peak resolution than MeOH and Saponin permeabilization.•Non-specific antibody binding in neutrophils can be efficiently blocked by using 1% BSA and non-immune goat serum.

Multiparameter cytometric analysis of complex cellular response

Complex analysis of cellular responses after experimental treatment is important for screening, mechanistic understanding of treatment effects, and the identification of sensitive and resistant cell phenotypes. Modern multicolor flow cytometry has demonstrated its power for such analyses. Here, we introduce a multiparametric protocol for complex analysis of cytokinetics by the simultaneous detection of seven fluorescence parameters. This analysis includes the detection of two surface markers for immunophenotyping, analysis of proliferation based on the cell cycle and the measurement of incorporated nucleoside analogue 5-ethynyl-2'-deoxyuridine (EdU) in newly synthesized DNA, analysis of DNA damage using an anti-phospho-histone H2A.X (Ser139) antibody, and determination of cell death using a fixable viability probe and intracellular detection of caspase-3 activation. To demonstrate the applicability of this protocol for the analysis of heterogeneous and complex cell responses, we used different treatments and model cell lines. We demonstrated that this protocol has the potential to provide complex and simultaneous analysis of cytokinetics and analyze the heterogeneity of the response at the single-cell level. © 2017 International Society for Advancement of Cytometry.

Nuclear translocation of STAT3 and NF-κB are independent of each other but NF-κB supports expression and activation of STAT3

NF-κB and STAT3 are essential transcription factors in immunity and act at the interface of the transition from chronic inflammation to cancer. Different functional crosstalks between NF-κB and STAT3 have been recently described arguing for a direct interaction of both proteins. During a systematic analysis of NF-κB/STAT3 crosstalk we observed that appearance of the subcellular distribution of NF-κB and STAT3 in immunofluorescence heavily depends on the fixation procedure. Therefore, we established an optimized fixation protocol for the reliable simultaneous analysis of the subcellular distributions of both transcription factors. Using this protocol we found that cytokine-induced nuclear accumulation of NF-κB or STAT3 did not alter the subcellular distribution of the other transcription factor. Both knockout and overexpression of STAT3 does not have any major effect on canonical TNFα-NF-κB signalling in MEF or HeLa cells. Similarly, knockout of p65 did not alter nuclear accumulation of STAT3 in response to IL-6. However, p65 expression correlates with elevated total cellular levels of STAT3 and STAT1 and supports activation of these transcription factors. Our findings in MEF cells argue against a direct physical interaction of free cellular NF-κB and STAT3 but point to more intricate functional interactions.

Antigen Masking During Fixation and Embedding, Dissected

Antigen masking in routinely processed tissue is a poorly understood process caused by multiple factors. We sought to dissect the effect on antigenicity of each step of processing by using frozen sections as proxies of the whole tissue. An equivalent extent of antigen masking occurs across variable fixation times at room temperature. Most antigens benefit from longer fixation times (>24 hr) for optimal detection after antigen retrieval (AR; for example, Ki-67, bcl-2, ER). The transfer to a graded alcohol series results in an enhanced staining effect, reproduced by treating the sections with detergents, possibly because of a better access of the polymeric immunohistochemical detection system to tissue structures. A second round of masking occurs upon entering the clearing agent, mostly at the paraffin embedding step. This may depend on the non-freezable water removal. AR fully reverses the masking due both to the fixation time and the paraffin embedding. AR itself destroys some epitopes which do not survive routine processing. Processed frozen sections are a tool to investigate fixation and processing requirements for antigens in routine specimens.

Measurement of PTEN by Flow Cytometry

Recent advancements have driven the development of smaller footprint, less expensive, and user-friendly flow cytometers introducing the technology to more users.Flow cytometry is an established tool for multiparametric analysis of various important cellular characteristics. Fluorescent dyes or fluorophore-conjugated antibodies allow for measurement of protein expression, identification of cell populations, or DNA content analysis. This is combined with analysis of light-scattering detection to determine cell size and complexity to allow for the study of complex cell samples, such as whole blood. Through antibody staining for a variety of surface markers as well as intracellular proteins we can also elucidate intracellular signaling, and phosphor-signaling, on a single-cell basis.Here we describe the application of flow cytometry analysis to the tumor suppressor PTEN in various cancer cell lines and a mouse model.

Diet-induced obesity modulates epigenetic responses to ionizing radiation in mice

Both exposure to ionizing radiation and obesity have been associated with various pathologies including cancer. There is a crucial need in better understanding the interactions between ionizing radiation effects (especially at low doses) and other risk factors, such as obesity. In order to evaluate radiation responses in obese animals, C3H and C57BL/6J mice fed a control normal fat or a high fat (HF) diet were exposed to fractionated doses of X-rays (0.75 Gy ×4). Bone marrow micronucleus assays did not suggest a modulation of radiation-induced genotoxicity by HF diet. Using MSP, we observed that the promoters of p16 and Dapk genes were methylated in the livers of C57BL/6J mice fed a HF diet (irradiated and non-irradiated); Mgmt promoter was methylated in irradiated and/or HF diet-fed mice. In addition, methylation PCR arrays identified Ep300 and Socs1 (whose promoters exhibited higher methylation levels in non-irradiated HF diet-fed mice) as potential targets for further studies. We then compared microRNA regulations after radiation exposure in the livers of C57BL/6J mice fed a normal or an HF diet, using microRNA arrays. Interestingly, radiation-triggered microRNA regulations observed in normal mice were not observed in obese mice. miR-466e was upregulated in non-irradiated obese mice. In vitro free fatty acid (palmitic acid, oleic acid) administration sensitized AML12 mouse liver cells to ionizing radiation, but the inhibition of miR-466e counteracted this radio-sensitization, suggesting that the modulation of radiation responses by diet-induced obesity might involve miR-466e expression. All together, our results suggested the existence of dietary effects on radiation responses (especially epigenetic regulations) in mice, possibly in relationship with obesity-induced chronic oxidative stress.

Validation of cell-based fluorescence assays: practice guidelines from the ICSH and ICCS - part III - analytical issues

Clinical diagnostic assays, may be classified as quantitative, quasi-quantitative or qualitative. The assay's description should state what the assay needs to accomplish (intended use or purpose) and what it is not intended to achieve. The type(s) of samples (whole blood, peripheral blood mononuclear cells (PBMC), bone marrow, bone marrow mononuclear cells (BMMC), tissue, fine needle aspirate, fluid, etc.), instrument platform for use and anticoagulant restrictions should be fully validated for stability requirements and specified. When applicable, assay sensitivity and specificity should be fully validated and reported; these performance criteria will dictate the number and complexity of specimen samples required for validation. Assay processing and staining conditions (lyse/wash/fix/perm, stain pre or post, time and temperature, sample stability, etc.) should be described in detail and fully validated.

Nanopodia--thin, fragile membrane projections with roles in cell movement and intercellular interactions

Adherent cells in culture maintain a polarized state to support movement and intercellular interactions. Nanopodia are thin, elongated, largely F-actin-negative membrane projections in endothelial and cancer cells that can be visualized through TM4SF1 (Transmembrane-4-L-six-family-1) immunofluorescence staining. TM4SF1 clusters in 100-300 μm diameter TMED (TM4SF1 enriched microdomains) containing 3 to as many as 14 individual TM4SF1 molecules. TMED are arranged intermittently along nanopodia at a regular spacing of 1 to 3 TMED per μm and firmly anchor nanopodia to matrix. This enables nanopodia to extend more than 100 μm from the leading front or trailing rear of polarized endothelial or tumor cells, and causes membrane residues to be left behind on matrix when the cell moves away. TMED and nanopodia have been overlooked because of their extreme fragility and sensitivity to temperature. Routine washing and fixation disrupt the structure. Nanopodia are preserved by direct fixation in paraformaldehyde (PFA) at 37 °C, followed by brief exposure to 0.01% Triton X-100 before staining. Nanopodia open new vistas in cell biology: they promise to reshape our understanding of how cells sense their environment, detect and identify other cells at a distance, initiate intercellular interactions at close contact, and of the signaling mechanisms involved in movement, proliferation, and cell-cell communications. The methods that are developed for studying TM4SF1-derived nanopodia may be useful for studies of nanopodia that form in other cell types through the agency of classic tetraspanins, notably the ubiquitously expressed CD9, CD81, and CD151.

Combined flow cytometric analysis of surface and intracellular antigens reveals surface molecule markers of human neuropoiesis

Surface molecule profiles undergo dynamic changes in physiology and pathology, serve as markers of cellular state and phenotype and can be exploited for cell selection strategies and diagnostics. The isolation of well-defined cell subsets is needed for in vivo and in vitro applications in stem cell biology. In this technical report, we present an approach for defining a subset of interest in a mixed cell population by flow cytometric detection of intracellular antigens. We have developed a fully validated protocol that enables the co-detection of cluster of differentiation (CD) surface antigens on fixed, permeabilized neural cell populations defined by intracellular staining. Determining the degree of co-expression of surface marker candidates with intracellular target population markers (nestin, MAP2, doublecortin, TUJ1) on neuroblastoma cell lines (SH-SY5Y, BE(2)-M17) yielded a combinatorial CD49f^-/CD200^high surface marker panel. Its application in fluorescence-activated cell sorting (FACS) generated enriched neuronal cultures from differentiated cell suspensions derived from human induced pluripotent stem cells. Our data underlines the feasibility of using the described co-labeling protocol and co-expression analysis for quantitative assays in mammalian neurobiology and for screening approaches to identify much needed surface markers in stem cell biology.

Single-cell phospho-protein analysis by flow cytometry

This protocol describes methods for monitoring intracellular phosphorylation-dependent signaling events on a single-cell basis. This approach measures cell signaling by treating cells with exogenous stimuli, fixing cells with formaldehyde, permeabilizing with methanol, and then staining with phospho-specific antibodies. Thus, cell signaling states can be determined as a measure of how cells interact with their environment. This method has applications in clinical research as well as mechanistic studies of basic biology. In clinical research, diagnostic or drug efficacy information can be retrieved by discovering how a disease affects the ability of cells to respond to growth factors. Basic scientists can use this technique to analyze signaling events in cell lines and human or murine primary cells, including rare populations, like B1 cells or stem cells. This technique has broad applications bringing standard biochemical analysis into primary cells in order to garner valuable information about signaling events in physiologic settings.

Immunolabeling artifacts and the need for live-cell imaging

Fluorescent fusion proteins have revolutionized examination of proteins in living cells. Still, studies using these proteins are met with criticism because proteins are modified and ectopically expressed, in contrast to immunofluorescence studies. However, introducing immunoreagents inside cells can cause protein extraction or relocalization, not reflecting the in vivo situation. Here we discuss pitfalls of immunofluorescence labeling that often receive little attention and argue that immunostaining experiments in dead, permeabilized cells should be complemented with live-cell imaging when scrutinizing protein localization.

Cytofluorometric detection of rodent malaria parasites using red-excited fluorescent dyes

Flow cytometry is a potentially efficient approach for the quantification of parasitemias in experimental malaria infections and drug susceptibility assays using rodent malaria models such as Plasmodium berghei. In this study, we used two red DNA-binding fluorochromes, rhodamine 800 (R800) and LD700, to measure parasitemia levels in whole blood samples from mice infected with P. berghei. Blood samples were treated with RNAse A to eliminate RNA-derived signals. Propidium iodide, which stains both DNA and RNA, was used as a positive control. The parasitemia levels determined by R800 and LD700 were comparable to those calculated by microscopic analysis of blood smears and flow cytometry using Hoechst 33258. RNAse treatment did not affect these measurements. We also used R800 or LD700 to quantify parasitemias in mice infected with a GFP-expressing P. berghei line to correlate the parasitemia levels determined by DNA staining versus parasite numbers using GFP fluorescence as a surrogate measurement. A positive correlation was found between levels determined by flow cytometry using these dyes and those measured by GFP expression. Similar results were obtained when parasitemias determined by flow cytometry were compared to those determined by conventional microscopy. The limit of detection of infected red blood cells using R800 or LD700 staining was 0.1% and 0.15%, respectively. This study demonstrates that red laser-based flow cytometry using R800 or LD700 can be used for effective quantification of parasitemia levels in Plasmodium infected red blood cells. Furthermore, this method has the advantage that it does not require RNAse pretreatment and allows for a greater amount of cells to be analyzed for parasite burden than otherwise measured by conventional microscopy. © 2011 International Society for Advancement of Cytometry.

Techniques for dual staining of DNA and intracellular immunoglobulins in murine hybridoma cells: applications to cell-cycle analysis of hyperosmotic cultures

Flow cytometry was used to evaluate the effects of hyperosmotic stress on cell-cycle distribution and cell-associated immunoglobulins for murine hybridoma cells grown in batch culture. Paraformaldehyde/methanol fixation substantially increased the fluorescence signal for intracellular immunoglobulins compared to ethanol fixation. For surface immunoglobulins, similar fluorescence signals were observed regardless of fixation method. Dual staining of immunoglobulins and cellular DNA was employed to determine immunoglobulin pool size as a function of cell-cycle phase. The intracellular immunoglobulin pool sizes increased as the cells progressed through the cell cycle for both control and hyperosmotic cultures. For control cultures, the immunoglobulin pool size increased during the exponential phase of culture, followed by a decrease as the cultures entered stationary phase. In contrast, hyperosmotic cultures showed an initial decrease in immunoglobulin pool size upon the application of osmotic shock, followed by an increase to a level above that of control cultures. This behavior was observed in all phases of the cell cycle. In addition, hyperosmotic cultures exhibited an increase in cell size when compared to control cultures. When normalized for cell size, the intracellular immunoglobulin concentration in hyperosmotic cultures was initially lower than in control cultures and subsequently increased to slightly above the level of control cells. Cells in all phases of the cell cycle behaved in a similar manner. There was no apparent relationship between the intracellular antibody concentration and the rate of antibody secretion.

Indirect immunofluorescent labeling of fixed cells

Flow cytometry protocols for defining cell surface or intracellular antibody staining are discussed. Various staining protocols are provided. Routine cell surface and intracellular techniques as well as more advanced signal enhancement techniques are detailed.

Simultaneous characterization of phospho-proteins and cell cycle in activated T cell subsets

Multi-colour flow cytometry is the only technological platform that can analyse the highly complex cellular composition of the immune system in parallel and at a single cell resolution. Analysis of the T cell compartment, in particular, requires the simultaneous measurement of multiple markers in order to account for lineage, phenotype and function. Flow cytometry also enables the analysis of intracellular signalling events. By combining the expression of surface markers, intracellular cytokines, phosphorylated versus unphosphorylated kinases, cell proliferation and DNA profile, mechanistic and kinetic information of subset-specific signalling may be obtained: this has not previously been achieved. Here we present a protocol which permits all of these aspects to be explored simultaneously. By comparing basic procedures previously described we were able to optimise different variables, including the choice of antibody/fluorochrome pairs, permeabilisation, fixation and labelling time, to obtain the best DNA staining of different cell types. We applied this method to study subset-specific signalling related to cytokine production and DNA synthesis in T cells responding to specific antigens.

Salinity stress results in rapid cell cycle changes of tilapia (Oreochromis mossambicus) gill epithelial cells

We have developed a technique for immunocytochemistry of fish gill cells that we used to quantify tilapia (Oreochromis mossambicus) mitochondria-rich cells (MRC) and other gill cells (non-MRC) within different cell cycle phases by laser scanning cytometry. Gill cells fixed on coverslips were triple stained with propidium iodide to distinguish G1 vs. G2 phases, Ser10-phosphorylated histone H3 antibody to label mitotic cells, and Na(+)/K(+) ATPase antibody to label MRC. These parameters were measured at 0 (control), 4, 8, 16, 24, 48, 72, and 168 hr (1 week) following exposure of freshwater (FW) acclimated fish to 2/3 seawater (SW). MRC increased mitotic activity very rapidly peaking at 8 hr following SW exposure. This change in mitotic MRC is indicative of epithelial reorganization during SW acclimation. In contrast to MRC, the proportion of non-MRC (likely pavement cells (PVC)) in mitosis did not change significantly in response to SW exposure. Moreover, twice as many MRC were in mitosis compared with non-MRC, suggesting that MRC turn over faster than other cell types during SW acclimation. Following the mitosis peak, MRC accumulated in G2 phase over a period of 16-72 hr post-SW exposure. We also observed G2 arrest with similar kinetics following SW exposure in tilapia non-MRC (likely PVC). We interpret the G2 arrest that occurs after an initial wave of transient increase in MRC mitosis as a means for conserving energy for dealing with the osmotic stress imposed during the exposure of FW fish to SW.

Single-cell phospho-protein analysis by flow cytometry

This protocol describes methods for monitoring intracellular phosphorylation-dependent signaling events on a single-cell basis. This approach measures cell signaling by treating cells with exogenous stimuli, fixing cells with formaldehyde, permeabilizing with methanol, and then staining with phospho-specific antibodies. Thus, cell signaling states can be determined as a measure of how cells interact with their environment. This method has applications in clinical research as well as mechanistic studies of basic biology. In clinical research, diagnostic or drug efficacy information can be retrieved by discovering how a disease affects the ability of cells to respond to growth factors. Basic scientists can use this technique to analyze signaling events in cell lines and human or murine primary cells, including rare populations, like B1 cells or stem cells. This technique has broad applications to take standard biochemical analysis into primary cells to garner valuable information about signaling events in physiologic settings.

Flow acetone-staining technique: a highly efficient procedure for the simultaneous analysis of DNA content, cell morphology, and immunophenotype by flow cytometry

The accurate determination of cell cycle, immunophenotypes and morphology at single-cell level is not fully achieved by current flow cytometry protocols. Acetone, a coagulant fixative/permealizing agent, is widely used in static cytometry, but is impractical in flow cytometry because of its shrinking effect. We sought for conditions of acetone treatment that could permit the simultaneous analysis of physical parameters, surface and intracellular immunostaining, and DNA content. We evaluated different experimental conditions (concentration, duration of fixation, temperature, presence of proteins) to test the capacity of acetone fixation/permeabilization to preserve cell physical parameters (forward and side scatters, FSC, and SSC) and immunophenotyping while allowing stoichiometric DNA staining. The commonly used ethanol fixation technique was used as reference method. To detect phenotypes and DNA content simultaneously, we employed 7-aminoactinomycin D (7-AAD) as "intercalating" dye for DNA in spite of, or just for, its controversial ability in stoichiometric DNA staining. Cells were resting peripheral blood monucleated cells (PBMCs), T- and B-cell blasts obtained by PBMCs stimulation, and the human cell lines Ramos and Shep. Acetone fixation, preserving both the recovery and the physical parameters of cells, is drastically influenced by temperature of treatment and is practicable only when the protocol is realized at 8 degrees C. Under this condition, acetone maintains the immunophenotypic fluorescences (realized before or after the fixation) better than ethanol. Stoichiometric DNA staining of acetone processed cells, the variation coefficients (CV) of frequency distributions of G1/G0 and G2/M phases, the modes ratio of these distributions and doublets generation are at least comparable to those obtained with ethanol treatment. The assay developed in the present study, that we called flow acetone-staining technique (FAST), accurately analyzes cell cycle, physical parameters and immunophenotypes in heterogenous cell populations, and thus provides a useful tool for cytomics.

African swine fever virus p10 protein exhibits nuclear import capacity and accumulates in the nucleus during viral infection

African swine fever virus (ASFV), a large enveloped DNA-containing virus, infects domestic and wild pigs, and multiplies in soft ticks, causing an economically relevant hemorrhagic disease. Evaluation of the nuclear import ability of ASFV p10 protein was the major purpose of the present work. Two approaches were used to determine if p10 protein is imported into the nucleus by an active process: a yeast-based nuclear import assay and the determination of the subcellular localization of p10 protein in mammalian cells by fluorescence microscopy. The results obtained clearly demonstrate that p10 protein is actively imported into the nucleus, both in yeast and mammalian cells. Experiments aiming at identifying the critical residues responsible for the nuclear import of ASFV p10 protein indicate that the amino acids comprised between the positions 71 and 77 are important, although not sufficient, for the protein active nuclear import. In ASFV-infected cells, the p10 protein strongly accumulates in the nucleus at late times post-infection, indicating that p10 protein may accomplish an important function inside the nucleus during the late phase of the viral replication cycle.

Changes in fluorescence intensity of selected leukocyte surface markers following fixation

BACKGROUND

Immunophenotyping of blood leukocytes often involves fixation with paraformaldehyde prior to cytometry analysis. However, the influence of cell type and marker specificity on the stability of fluorescence intensity after fixation has not been well studied.

METHODS

Human whole blood was stained using a panel of fluorescein isothiocyanate-labeled antibodies to surface markers. Unfixed and fixed samples were analyzed by flow cytometry at 0, 2, 4, 6, 24, 48, and 96 h after staining. Fluorescence measurements were converted to molecules of equivalent soluble fluorochrome for comparison.

RESULTS

Fixation caused a significant decrease in both forward and side scatter at 48 h which required gating adjustments to achieve resolution of cell populations. The autofluorescence increased progressively in fixed samples (ninefold at 96 h for monocytes). Variable decreases in marker-associated fluorescence became apparent after correction for autofluorescence. The magnitude of the decrease at 96 h varied with cell type and marker, from 5% for CD32 on monocytes to 39% for CD16 on neutrophils.

CONCLUSION

The change in fluorescence intensity following staining and fixation of leukocytes varies with cell type and surface marker. Fluorescence stability should be determined for each cell type and marker used, and the confounding effects of fixation on cell autofluorescence should be considered.

HER2 expression as a potential marker for response to therapy targeted to the EGFR

Since human epidermal growth factor receptor 2 (HER2) is known to participate with the epidermal growth factor receptor (EGFR) in mitogenic signalling, we hypothesised that HER2 overexpression might indicate responsiveness to EGFR targeted therapies. MCF7 breast cancer cells transfected with the HER2 gene were subcloned to establish a set of genetically related cell lines expressing graded levels of HER2 by immunoblot analysis. The subcloned cell lines and parental MCF7 cells were characterised by their growth characteristics, and cell by cell patterns of EGFR, HER2 and HER3 expression as well as levels of phosphorylated mitogen-activated protein kinase (MAPK) and AKT by laser scanning cytometry (LSC). Growth inhibition assays were used to characterise response to EGFR targeted therapy, and to determine the relationship between therapeutic response and levels of tyrosine kinase expression. The levels of growth inhibition of AG1478 and of the AG1478-trastuzumab combinations were correlated with levels of HER2 expression among the different cell lines. Among EGFR, HER2 and HER3, HER2 overexpression was the best single predictive marker, but combinations of two markers provided additional predictive information.

A flow cytometry procedure for simultaneous characterization of cell DNA content and expression of intracellular protein kinase C-zeta

A selective involvement of protein kinase C-zeta (PKC-zeta) in the events regulating cell proliferation has been recently proposed. Here we report a flow cytometric method allowing the simultaneous association of intracellular PKC-zeta expression or phosphorylation with each cell cycle phase. Current methods for flow cytometry analysis were applied to several cell lines and compared to the method developed in our laboratory. The latter includes 2% paraformaldehyde (PFA), as fixing agent, a permeabilization/saturation step by means of a solution containing 150 mM NaCl, 5 mM EDTA, 50 mM Tris-HCl pH 7.4, 0.05% NP-40, 0.25% lambda-carrageenan and 0.02% NaN3, followed by labelling with a primary antibody (PKC-zeta or P-PKC-zeta) and with the appropriate FITC-conjugated secondary antibody. Cells processed by such a method disclosed no substantial modification of light scattering features with respect to live cells. In addition, stainability with anti-PKC-zeta or anti-P-PKC-zeta antibodies was well preserved while stoichiometric staining of DNA with PI enabled accurate cell cycle analysis. Results show that a distinct up-regulation of P-PKC-zeta in G2/M phase occurs. The method here described, therefore, represents a simple, reproducible and conservative assay for a simultaneous assessment of intracellular PKC or P-PKC modulations within each cell cycle phase.

Guidelines for improving the reproducibility of quantitative multiparameter immunofluorescence measurements by laser scanning cytometry on fixed cell suspensions from human solid tumors

BACKGROUND

Laser scanning Cytometry (LSC) is a versatile technology that makes it possible to perform multiple measurements on individual cells and correlate them cell by cell with other cellular features. It would be highly desirable to be able to perform reproducible, quantitative, correlated cell-based immunofluorescence studies on individual cells from human solid tumors. However, such studies can be challenging because of the presence of large numbers of cell aggregates and other confounding factors. Techniques have been developed to deal with cell aggregates in data sets collected by LSC. Experience has also been gained in addressing other key technical and methodological issues that can affect the reproducibility of such cell-based immunofluorescence measurements.

METHODS AND RESULTS

We describe practical aspects of cell sample collection, cell fixation and staining, protocols for performing multiparameter immunofluorescence measurements by LSC, use of controls and reference samples, and approaches to data analysis that we have found useful in improving the accuracy and reproducibility of LSC data obtained in human tumor samples. We provide examples of the potential advantages of LSC in examining quantitative aspects of cell-based analysis. Improvements in the quality of cell-based multiparameter immunofluorescence measurements make it possible to extract useful information from relatively small numbers of cells. This, in turn, permits the performance of multiple multicolor panels on each tumor sample. With links among the different panels that are provided by overlapping measurements, it is possible to develop increasingly more extensive profiles of intracellular expression of multiple proteins in clinical samples of human solid tumors. Examples of such linked panels of measurements are provided.

CONCLUSIONS

Advances in methodology can improve cell-based multiparameter immunofluorescence measurements on cell suspensions from human solid tumors by LSC for use in prognostic and predictive clinical applications.

A simple correction for cell autofluorescence for multiparameter cell-based analysis of human solid tumors

BACKGROUND

Corrections that have been proposed to minimize the unwanted contribution of cell autofluorescence to the total fluorescence signal often require either specialized instrumentation or the sacrifice of a data channel so as to perform a measurement that can be used to correct for autofluorescence in individual cells. Here we propose a simple cell by cell correction for autofluorescence that is suitable for multiparameter laser scanning cytometry (LSC) studies in human solid tumors that relies on the ratio of mean autofluorescence to mean total cell fluorescence (mean Flauto/mean Fltotal). This approach assumes a correlation between the autofluorescence component and the total signal in individual cells. This correction does not require specialized instrumentation, and does not sacrifice a data channel in multiparameter studies. A potential disadvantage is that errors may be introduced by the assumption of a correlation between the two components of the total fluorescence signal in individual cells in samples in which no such correlation exists.

METHODS

Distributions of cell autofluorescence and total Her-2/neu cell fluorescence were obtained separately by LSC in three human breast cancer cell lines and in three samples of primary human lung cancer. In the breast cancer cell lines, autofluorescence measurements and Her-2/neu measurements were also obtained on the same cells.

RESULTS

We show that there is a partial correlation between autofluorescence and total Her-2/neu/FITC fluorescence in individual cells in the three breast cancer cell lines. We also show that the results of a ratio-based autofluorescence correction agree with those based on a true cell by cell correction. Computer simulation studies suggest that in samples with no correlation between the autofluorescence component and the true probe/dye fluorescence component, the ratio correction produces robust estimates of the mean true fluorescence signal, with relatively small but systematic underestimates of the coefficient of variation of such measurements under conditions commonly encountered in the measurement of human solid tumors.

CONCLUSIONS

A simple cell by cell correction for autofluorescence based on the ratio of mean Flauto to mean Fltotal can be applied in cell samples in which there is a correlation between cell autofluorescence and true probe/dye fluorescence in individual cells. In cell samples that lack this correlation, or in which it is not known whether such a correlation exists, this correction can be used with the reservation that there is a systematic but relatively small underestimation of the degree of variability of the measurements.

Coordinate analysis of murine immune cell surface markers and intracellular phosphoproteins by flow cytometry

Recently, phosphospecific flow cytometry has emerged as a powerful tool to analyze intracellular signaling events in complex populations of cells because of its ability to simultaneously discriminate cell types based on surface marker expression and measure levels of intracellular phosphoproteins. This has provided novel insights into the cell- and pathway-specific nature of immune signaling. However, we and others have found that the fixation and permeabilization steps necessary for phosphoprotein analysis often negatively affect the resolution of cell types based on surface marker analysis and light scatter characteristics. Therefore, we performed a comprehensive profile of >35 different murine surface marker Abs to understand the effects of fixation and permeabilization on surface Ag staining. Fortuitously, approximately 80% of the Abs tested resolved cell populations of interest, although with decreased separation between positive and negative populations and at very different titers than those used on live cells. The other 20% showed either complete loss of separation between populations or loss of intermediately staining populations. We were able to rescue staining of several of these Ags by performing staining after fixation, but before permeabilization, although with limited fluorophore choices. Scatter characteristics of lymphocytes were well retained, but changed dramatically for monocyte and neutrophil populations. These results compile a comprehensive resource for researchers interested in applying phosphospecific flow cytometry to complex populations of cells while outlining steps necessary to successfully apply new surface marker Abs to this platform.

Intracellular patterns of Her-2/neu, ras, and ploidy abnormalities in primary human breast cancers predict postoperative clinical disease-free survival

PURPOSE

In an earlier study, the presence of aneuploidy, Her-2/neu overexpression, and ras overexpression in the same cells (triple-positive cells) was of prognostic significance (P < 0.015) in 91 patients with localized breast cancer (median follow up, 32 months). Here, we present results involving a larger group of patients with longer follow-up.

EXPERIMENTAL DESIGN

Fixed cell suspensions prepared from primary tumors of 189 patients with early breast cancer were studied prospectively by multiparameter flow cytometry. Correlated intracellular fluorescence-based measurements of cell DNA content and Her-2/neu and ras protein were obtained on each of >2000 cells in each tumor. Intracellular combinations of abnormalities in these measurements were correlated with subsequent patient disease-free survival (DFS). Median time on study was 54 months (range, 7-128 months).

RESULTS

DFS of patients with > or = 5% triple-positive tumor cells was shorter than those who did not meet this criterion (P = 0.004). The difference remained statistically significant after accounting for nodal status, tumor size, and each of the component abnormalities (P = 0.006). Node-negative patients whose tumors had fewer than 2 abnormalities/cell had an especially favorable clinical course, with a 5-year DFS of 96% (lower confidence bound, 86%).

CONCLUSIONS

Patterns of accumulated intracellular molecular abnormalities in cells of primary human breast cancers are predictive for subsequent DFS independently of the abnormalities themselves taken individually.

Proliferating keratinocytes are putative sources of the psoriasis susceptibility-related EDA+ (extra domain A of fibronectin) oncofetal fibronectin

The extra domain A of fibronectin (EDA+ oncofetal isoform of fibronectin was recently reported to be overexpressed in psoriatic uninvolved epidermis. It has been proposed that the abnormal presence of EDA+ oncofetal protein at the dermal-epidermal junction in the uninvolved skin may provide the "psoriatic" environment in which keratinocytes are in a preactivated state with regard to mitogenic signals (e.g., T cell lymphokines). To determine the possible sources of cellular fibronectin in the non-lesional psoriatic skin, we aimed to investigate whether keratinocytes could produce the EDA+ oncofetal form of fibronectin. RT-PCR studies revealed that both cultured normal keratinocytes and HaCaT cells express the EDA+ splice variant of fibronectin mRNA, and in HaCaT cells the EDA+/EDA- transcript ratio was elevated compared with normal keratinocytes. Cultured keratinocytes and HaCaT cells showed intracytoplasmic staining with an EDA+ fibronectin-specific antibody and among the positively stained cells many showed mitosis. Using RT-PCR, western blot analysis, and flow cytometry, we showed that in synchronized HaCaT cells the amount of both total fibronectin and its EDA+ isoform change with the proliferation/differentiation state of HaCaT cells and peak in highly proliferating cells. We show that in short-term ex vivo cultures, a small population of EDA+ fibronectin containing cell population appear among psoriatic uninvolved, but not normal epidermal cells. We also demonstrate that cell attachment has a strong influence on the expression of both total and EDA+ fibronectin. Our results suggest that proliferating keratinocytes could be the sources of the psoriasis susceptibility-related EDA+ oncofetal fibronectin in the epidermis.

A suitable method for identifying cell aggregates in laser scanning cytometry listmode data for analyzing disaggregated cell suspensions obtained from human cancers

BACKGROUND

The presence of cell aggregates in cell suspensions obtained from human solid tumors can interfere with the measurement of cell DNA content of cell singlets, and can confound multiparameter analysis of other measurements on the same cells. Flow cytometric corrections for cell aggregates based on signal pulse shape have not proven to be reliable. Mathematical models have been developed to correct for cell aggregates in binned DNA histogram data, but they are not suitable for the correction of correlated non-DNA measurements obtained on the same cells.

METHODS

A total of 21 samples representing a variety of normal and malignant human cell types, including normal lymphocytes, normal sputum, human breast cancer cell lines, and mechanically disaggregated cell suspensions from primary breast cancers and nonsmall cell lung cancers, were studied by laser scanning cytometry (LSC) using the CompuCyte laser scanning cytometer (Cambridge, MA). Nuclear area, nuclear perimeter, and an LSC-based cell texture parameter were measured on approximately 400 cells in each sample, using an air-cooled, violet laser emitting at a wavelength of 405 nm for DAPI excitation, and each cell was classified as a singlet or aggregate by its appearance under direct observation. A "saddle function" provided by CompuCyte was used, together with an algorithm based on the measurements of nuclear area, perimeter, and cell texture (the APT algorithm), to identify cell aggregates and exclude them from the listmode data file.

RESULTS

Proportions of cell aggregates in the uncorrected samples ranging from 6 to 56% (mean, 20%) were reduced to proportions ranging from 0 to 7% (mean, 2.4%) after correction. The discriminant function was "tuned" to maintain both average cell singlet purity and average cell singlet yield at >70% over a broad range of cell DNA contents.

CONCLUSIONS

A combined approach to cell aggregate detection, which utilizes both the saddle function and the APT algorithm, produces list mode data files that exclude >80% of cell aggregates from samples of disaggregated cell suspensions of human tumors and other sources of clinical material. Such data files are suitable for multiparameter analysis.

Iron deprivation induces apoptosis independently of p53 in human and murine tumour cells

Iron deprivation induces apoptosis in some sensitive cultured tumour cells, while other cells are resistant. In order to elucidate the mechanisms involved in apoptosis induction by iron deprivation, we studied the expression of p53 and the expression of selected p53-regulated genes. To discriminate between changes coupled only with iron deprivation and changes involved in apoptosis induction by iron deprivation, we compared the expression of the genes in sensitive (human Raji, mouse 38C13) versus resistant (human HeLa, mouse EL4) cells under iron deprivation. Iron deprivation was achieved by incubation in a defined iron-free medium. The level of p53 mRNA decreased significantly under iron deprivation in sensitive cells, but it did not change in resistant cells. On the contrary, the level of the p53 protein under iron deprivation was slightly increased in sensitive cells while it was not changed in resistant cells. The activity of p53 was assessed by the expression of selected p53-regulated targets, i.e. p21(WAF1/CIP1) gene, mdm2, bcl-2 and bax. We did not detect any relevant change in mRNA levels as well as in protein levels of these genes under iron deprivation with the exception of p21(WAF1/CIP1). We detected a significant increase in the level of p21 mRNA in both (sensitive and resistant) mouse cell lines tested, however, we did not find any change in both (sensitive and resistant) human cell lines. Moreover, the p21(WAF1/CIP1) protein was accumulated in mouse-sensitive 38C13 cells under iron deprivation while all other cell lines tested, including human-sensitive cell line Raji, did not show any accumulation of p21(WAF1/CIP1) protein. It seems that the p21(WAF1/CIP1) mRNA, as well as protein accumulation, is not specifically coupled with apoptosis induction by iron deprivation and that it is rather cell-line specific. Taken together, we suggest that iron deprivation induces apoptosis at least in some cell types independently of the p53 pathway.

Bcl-2 promotes premature senescence induced by oncogenic Ras

The expression of the apoptosis inhibitory protein, Bcl-2, is increased in naturally senescing human fibroblasts and upon induction of their senescence-like growth arrest by oxidative stress, implying its role in maintaining their extended viability. Oncogenic Ras(V12) protein induces signaling cascades that result in the premature senescence of primary fibroblast cells, which are insensitive to oncogene-dependent apoptosis. Here we show that constitutive expression of Bcl-2 accelerates selected features of the Ras-induced senescence program in primary human fibroblasts. Yet, Bcl-2 also inhibits fibroblast apoptosis induced by exogenous H(2)O(2), while both signals induce an increased endogenous Bcl-2 expression in these cells. Together, these data suggest a context-dependent phenotypic function of Bcl-2 in the regulation of overlapping cell fate specification programs, with potential implications for both physiology and multistep tumorigenesis.

Higher pH promotes megakaryocytic maturation and apoptosis

Megakaryocytic (Mk) cells mature adjacent to bone marrow (BM) sinus walls and subsequently release platelets within the sinusoidal space or in lung capillaries. In contrast, primitive stem and Mk progenitor cells reside the furthest away from the BM sinus walls. The existence of pH gradients in the BM raises the question of whether pH affects Mk maturation and differentiation. We generated Mk cells from peripheral blood CD34(+) cells in a serum-free medium at different pH levels (7.2, 7.4, and 7.6) and found that higher pH resulted in an earlier and higher polyploidization of CD41(+) Mk cells and an earlier onset of Mk-cell apoptosis. The peak day of high ploidy was correlated well with the onset day of Mk apoptosis, thus suggesting that a decline in the fraction of high-ploidy Mk cells at the late culture stage is caused by Mk-cell apoptosis. We further explored the relationship between Mk-cell maturation and apoptosis by employing an antiapoptotic agent Z-Val-Ala-Asp(Ome)-FMK (zVAD). Addition of zVAD led to an average 30% higher and 2.8-day delayed polyploidization, while apoptosis was delayed by 2.4 days. Faster depletion of CD34(+) cells and an earlier peak in the fraction of larger colony-forming Mk cells (BFU-Mks) were also observed at higher pH. Taken together, these data suggest that higher pH promotes Mk-cell differentiation, maturation, and apoptosis.

Quantitation of baculovirus particles by flow cytometry

A method using flow cytometry (FCM) analysis was developed to quantitate baculovirus total particles produced in insect cell cultures. The method is a direct count of particles and involves staining of the baculovirus DNA with SYBR Green I, a highly fluorescent nucleic acid specific dye. Sample preparation of cell-free supernatant containing budded viral particles involves fixation with paraformaldehyde, freeze-thaw treatment, viral membrane permeabilization with Triton X-100, and sample heating to improve staining efficiency and enhance baculovirus particle green fluorescence intensities. In this study, the effects of the different treatment steps and medium composition on viral particle counts were examined in order to identify optimal preparation conditions. FCM analysis linearity was established over a viral concentration range of two logs with a lower detection limit at 10(5) viral particles per ml. Robustness and reproducibility of the method were assessed using samples from large-scale bioreactor cultures. The events (or virus particle counts) obtained by FCM analysis were usually higher than the titres obtained by end-point dilution assay (EPDA). Results from 16 different viral stocks showed an average ratio of 3.7 total particles (FCM) to infectious particles (EPDA). Essentially, the FCM analysis reported below shortens baculovirus quantitation time to 2 h and provides a good estimation of virus titers. It is believed that these findings will contribute to acceleration of process development in the area of baculovirus expression technology in general and specifically in process where stoichiometric multi-viral infections of cells are critical to the expression of complex products.

Influence of different radioprotective compounds on radiotolerance and cell cycle distribution of human progenitor cells of granulocytopoiesis in vitro

Ficoll-separated mononuclear cells (MNC) of cryopreserved human bone marrow were incubated with isotoxic doses of diltiazem, N-acetylcysteine (NAC), glycopolysaccharide extract of spirulina platensis (SPE), tempol, thiopental, WR2721 and WR1065. After irradiation with a single dose of 0.73 Gy, survival of granulocyte/macrophage colony-forming cells (GM-CFC) was determined at d 10-14, using an agar culture system. Diltiazem, NAC, tempol and WR1065 significantly improved radiotolerance with protection factors (PF) between 1.21 and 1.36 (n = 5, P < 0.05) at 0.73 Gy (PF-0.73 Gy). The survival curves of diltiazem (D0 = 0.88 Gy, n = 1.00), NAC (D0 = 0.92 Gy, n = 1.10), tempol (D0 = 0.99 Gy, n = 1.10), WR1065 (D0 = 0.89 Gy, n = 1.16) and control (D0 = 0.78 Gy, n = 1.00) over 0.36-2.91 Gy showed a significant radioprotective effect for D0 only for tempol (P = 0.018) and for the extrapolation number 'n' only in the case of NAC (P = 0.023). Cell cycle analysis of the CD34+ cell subpopulation (control-0 h: G1 = 82.7%, S = 13.7%, G2/M = 3.6%) revealed that all compounds with a significant PF-0.73 Gy also caused a significant increase in CD34+ cells in S phase up to 48 h. Within the first 24 h, only NAC (26.7 +/- 4.1%), tempol (14.3 +/- 1.0%) and possibly WR1065 (15.5 +/- 1.6%) had higher fractions of CD34+ S-phase cells compared with controls. This observation and the improvement of GM-CFC cloning efficiency indicated that only NAC was able to recruit progenitor cells in the cell cycle, whereas tempol and WR1065 possibly inhibited cell cycle progression by S and G2/M arrest. Of the radioprotectors tested, NAC, tempol and WR1065 may be suitable to support, alone or combined with cytokine therapy, accelerated haematopoietic recovery after irradiation.

Enhanced proliferative effects of a baculovirus-produced fusion protein of insulin-like growth factor and alpha(1)-proteinase inhibitor and improved anti-elastase activity of the inhibitor with glutamate at position 351

Alpha(1)-proteinase inhibitor (API) was coupled at the C-terminus of a human insulin-like growth factor (IGF) analog to facilitate its production in insect cells. This fusion protein significantly increased thymidine incorporation into HL-60 cells as compared with the incorporation observed with an equivalent molar mixture of the IGF analog and API. The M351E variant of API has been previously shown to reduce aggregate formation in prokaryotic expression systems. When the oxidation-sensitive methionine 351 of the inhibitor was changed to glutamate, the M351E variant was secreted in larger amounts from insect cells than the corresponding fusion protein with wild-type API. The M351E fusion protein and the corresponding chimera containing the wild-type API were tested for their capacity to inhibit human neutrophil elastase. The M351E variant was a more potent elastase inhibitor than the fusion protein containing the wild-type analog, whereas the proliferative activity of both chimeras was identical. The described mitogenic effect of the chimera and the improved anti-elastase activity of the M351E variant are two ideal properties for therapeutic agents acting in pathological situations where cell proliferation and inhibition of neutrophil elastase have to take place simultaneously, such as during wound healing.

Software compensation improves the analysis of heterogeneous tumor samples stained for multiparameter DNA flow cytometry

BACKGROUND

High concentrations of propidium iodide (PI), in combination with fluorescein isothiocyanate (FITC) and R-phycoerythrin (RPE) used for multiparameter DNA flow cytometry (FCM), cause spectral cross-talk into the green fluorescence channel (FL1). We have evaluated the use of post-acquisition software compensation (N-Color Compensation) in order to correct this spectral cross-talk caused by PI.

METHOD

Cell mixtures were prepared consisting of keratin 8/18 FITC labeled, keratin 8/18 RPE labeled, and unlabeled MCF-7 breast carcinoma cells. DNA was stained with PI (100 microM). Post-acquisition software compensation was applied to correct the spectral cross-talk of PI fluorescence. Secondly, the distribution of the Ki-67 (FITC) protein during the cell cycle (PI) of SiHa cervical carcinoma cells (no software compensation) was compared to the Ki-67 expression pattern of SiHa cells, simultaneously stained for keratin 8 (RPE), after applying software compensation. Finally, software compensation was used to compare the relative levels of PCNA and p53 expression in two clinical ovarian cancer ascites specimens, stained for PCNA or p53 (FITC), keratin 8/18 (RPE), and DNA (PI), with a known p53 status (positive and negative, respectively).

RESULTS

The Ki-67 cell cycle-dependent pattern of a triply stained sample (Ki-67 (FITC), keratin 8 (RPE), and DNA (PI)) is restored after software compensation and the results are comparable to the Ki-67 distribution of a sample stained solely for Ki-67 and DNA. P53 expression could only be resolved after using software compensation in the p53 positive ovarian ascites (OA) sample.

CONCLUSIONS

We conclude that software compensation is a robust and reliable post-acquisition method for the correction of RPE/PI spectral cross-talk, permitting better identification of weakly expressed proteins in heterogeneous clinical tumor samples stained for multiple cellular antigens and DNA using PI.