Wiley
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Bioreduction of water‐soluble tetrazolium salts (e.g., MTS, XTT, and MTT) to their respective formazans is generally regarded as an indicator of cell “redox activity.” The reaction is attributed mainly to mitochondrial enzymes and electron carriers. However, MTT reduction may also be catalyzed by a number of other nonmitochondrial enzymes. The goal of this work was to establish the sites of MTT reduction in intact HepG2 human hepatoma cells in culture.
In order to establish the subcellular localization of the sites of reduction of MTT, we imaged the formation of MTT‐formazan deposits using backscattered light confocal microscopy. Mitochondria were visualized in viable cells using fluorescent dyes that bind in a manner dependent (JC‐1 and TMRE) or independent (NAO) of mitochondrial electric potential.
Only 25–45% of MTT‐formazan was associated with mitochondria after 25 min of incubation. No more than 25% of the mitochondrial area on images was occupied by MTT‐formazan. Mitochondrial fluorescence of TMRE, NAO, and the monomeric form of JC‐1 decreased rapidly in cells incubated with MTT. However, the intensity of fluorescence of JC‐1 aggregates dropped by less than 30% at the onset of incubation and remained constant as reduction of MTT proceeded further.
(1) Most of MTT‐formazan deposits are not coincident with mitochondria. (2) Monomeric JC‐1, as well as TMRE and NAO, accumulating in mitochondria may be displaced by MTT. Thus, the presence of positively charged organic compounds (like MTT) may distort measurements of mitochondrial transmembrane electric potential, which are based on accumulation of fluorescent dyes. Cytometry 47:236–242, 2002. © 2002 Wiley‐Liss, Inc.
Integrin αIIbβ3 mediates platelet adhesion and aggregation and plays a crucial role in thrombosis and hemostasis. αIIbβ3 is expressed in a low affinity state on resting platelets. Upon platelet activation, αIIbβ3 shifts to a high affinity conformation that efficiently binds its ligands. On human platelets, the high affinity conformation of αIIbβ3 is detected by the monoclonal antibody (mAb), PAC‐1. However, a reagent with binding specificity to high affinity mouse αIIbβ3 has not been described so far.
A novel rat mAb directed against mouse αIIbβ3 (JON/A) was generated and characterized. JON/A was conjugated with fluorescein isothiocyanate (JON/AFITC) or with R‐phycoerythrin (JON/APE) and used for flow cytometric analysis of mouse platelets.
Although JON/AFITC bound to resting and activated platelets, virtually no binding of the larger JON/APE to resting platelets was detectable. However, strong binding of JON/APE occurred on platelet activation in a dose‐dependent manner. Binding of JON/APE required extracellular free calcium and was irreversible, thereby stabilizing the high affinity conformation of αIIbβ3.
JON/APE is the first tool for direct assessment of integrin αIIbβ3 activation in mice. Furthermore, JON/AFITC and JON/APE provide the first examples of fluorescent antibody derivatives with identical antigenic specificitiy that allow the discrimination between the resting and the activated state of an integrin. Cytometry 48:80–86, 2002. © 2002 Wiley‐Liss, Inc.
A method has been developed for reducing the intrinsic autofluorescence background component in cells labeled with fluorescent antibodies, thus permitting low levels of antibody‐binding on highly autofluorescent cells to be quantified. The method is based on the broad autofluorescent excitation spectra compared to the well‐defined spectra of the fluorescent label. Two laser wavelengths were used, one optimally to excite the fluorescent label plus autofluorescence and the second to excite only the autofluorescence. Two fluorescence measurements were made in the same wavelength region and the signals were subtracted on a cell‐by‐cell basis using a difference amplifier to zero the autofluorescence and amplify the signal from the fluorescent label. Test results on unlabeled autofluorescent macrophages showed that the autofluorescence component was reduced by balancing the signal inputs to the difference amplifier. When labeled macrophages were analyzed, the autofluorescence was reduced and the fluorescent‐labeled antibody‐binding component was amplified. The method was also able to resolve labeled lymphocytes from unlabeled autofluorescent macrophages.
Identification of nonviable cells in immunofluorescently stained cell populations is essential for obtaining accurate data. Fluorescent non‐vital DNA dyes, particularly propidium iodide (PI), have been used routinely in flow cytometry for discrimination of dead cells from viable cells on the basis of fluorescence. We describe here the use of an alternative DNA dye, 7‐amino‐actinomycin D (7‐AAD), which can replace PI for the exclusion of nonviable cells. As an example, we present in this paper the utilization of 7‐AAD on various leukemic cell lines for dead cell exclusion whenever the viable cell population could not be discriminated reliably from nonviable cells on the light scatter histogram; 7‐AAD is suitable for dead cell discrimination in lengthy experiments because it is efficiently excluded by intact cells and has a high DNA binding constant. In addition, the dye is valuable in combination with phycoerythrin (PE)‐fluorescence dual‐color flow cytometry on a single argon laser instrument, since its emission in the far red can easily be separated from the emission of PE; 7‐AAD was used on fluoresceinisothiocyanate (FITC) and PE surface‐labeled human thymocytes for characterization of the dying subpopulation of cells which is undergoing programmed cell death. In this heterogeneous cell preparation, the spectral properties of the dye permitted the classification of viable and nonviable cell subpopulations by multiparameter analysis.
The energy transfer efficiency E was measured between fluorescein‐conjugated concanavalin A (Con A) and rhodamine‐conjugated Con A bound to homogeneous tissue culture cells, the HK22 murine lymphoma cell line. Results from a flow cytometric energy transfer method (FCET) and two different steady‐state fluorimeter methods were compared. The data were found to be in close agreement after careful correction of the steady‐state fluorimetric measurements for contributions from dissociating ligand. The biological variability of the individual cells with respect to E was calculated using an error propagation analysis and were found to be less than the variability in the absolute amount of ligand binding per cell. FCET has a number of advantages over the fluorimetric measurements using suspensions of cells: (1) relatively labile receptor‐ligand complexes can be measured; (2) the analysis can be restricted to undamaged cells by gating the data collection on the light‐scattering signals; (3) heterogeneous populations of cells with respect to donor and acceptor topology can be distinguished by the correlation of E with other cellular parameters derived from additional signals or combinations thereof; and (4) the dynamics of donor‐acceptor redistribution on subpopulations can be measured.
Bài tổng quan này mô tả nhiều phương pháp để nhận diện và phân biệt giữa hai cơ chế chết tế bào khác nhau, apoptosis và hoại tử. Đa phần các phương pháp này đã được áp dụng trong các nghiên cứu về apoptosis trong dòng tế bào bạch cầu HL-60 của người bị kích hoạt bởi các chất ức chế DNA topoizomeras I hoặc II, và trong các tế bào tuyến ức của chuột bởi cả chất ức chế topoizomeras hoặc prednisolone. Trong hầu hết các trường hợp, apoptosis chọn lọc đối với tế bào trong pha nhất định của chu kỳ tế bào: chỉ tế bào HL-60 pha S và tế bào tuyến ức G0 bị ảnh hưởng chính. Hoại tử được kích hoạt bởi nồng độ quá cao của những loại thuốc này. Các đặc điểm tế bào sau đây đã được xác định có ích trong việc nhận diện kiểu chết tế bào: (a) Sự kích hoạt endonuclease trong tế bào apoptosis dẫn đến việc chiết xuất DNA có trọng lượng phân tử thấp sau khi tế bào bị thẩm thấu, dẫn đến giảm khả năng nhuộm bằng các fluoroquinone đặc hiệu với DNA. Đo hàm lượng DNA giúp nhận diện tế bào apoptosis và phát hiện được pha đặc hiệu của chu kỳ tế bào liên quan đến tiến trình apoptosis. (b) Tính toàn vẹn màng tế bào, mất trong tế bào hoại tử nhưng không mất trong tế bào apoptosis, đã được thăm dò bằng cách loại trừ iodua propidium (PI). Sự kết hợp giữa PI và Hoechst 33342 tỏ ra là một đầu dò tuyệt vời để phân biệt các tế bào sống, hoại tử, apoptosis sớm và muộn. (c) Điện thế xuyên màng ty thể, đo thông qua khả năng giữ rhodamine 123 được giữ nguyên trong tế bào apoptosis nhưng không trong tế bào hoại tử. (d) Bơm proton lysosome phụ thuộc vào ATP, thử nghiệm thông qua khả năng hút acridine orange (AO) trong môi trường sống, cũng được giữ nguyên trong tế bào apoptosis nhưng không trong tế bào hoại tử. (e) Phân tích bivariate của tế bào được nhuộm DNA và protein tiết lộ giảm đáng kể hàm lượng protein trong tế bào apoptosis, có lẽ do sự kích hoạt của protease nội sinh. Tế bào hoại tử, có màng bị rò, có hàm lượng protein tối thiểu. (f) Nhuộm RNA cho phép phân biệt giữa tế bào G0 và G1 và như vậy có thể chứng minh rằng apoptosis lựa chọn tế bào tuyến ức G0. (g) Sự giảm trong tán xạ ánh sáng phía trước, được đi kèm bởi hoặc không có thay đổi (tế bào HL-60) hoặc tăng (tế bào tuyến ức) của tán xạ góc phải, là những thay đổi sớm trong apoptosis. (h) Độ nhạy của DNA in situ đối với sự suy thoái, tăng trong tế bào apoptosis và tế bào hoại tử. Đặc điểm này, được thăm dò bằng cách nhuộm với AO ở pH thấp, cung cấp một thử nghiệm nhạy cảm và sớm để phân biệt giữa các tế bào sống, tế bào apoptosis và tế bào hoại tử, cũng như để đánh giá đặc điểm pha chu kỳ tế bào của các tiến trình này. (i) Phương pháp chuyển dịch nick in situ sử dụng triphospohonucloside gắn nhãn có thể được sử dụng để tiết lộ đứt gãy sợi DNA, để phát hiện giai đoạn rất sớm của apoptosis. Dữ liệu cho thấy rằng lưu lượng tế bào học có thể được áp dụng trong nghiên cứu cơ bản về cơ chế sinh hóa và phân tử của apoptosis, cũng như trong lâm sàng nơi khả năng theo dõi các dấu hiệu sớm của apoptosis trong các mẫu từ các khối u của bệnh nhân có thể dự đoán kết quả của một số phác đồ điều trị. © 1992 Wiley-Liss, Inc.
Flow cytometric energy transfer (FCET) measurements between labeled specific sites of cell surface elements (Szöllosi et al., Cytometry, 5:210–216, 1984) have been extended in a simplified form using a flow cytometer equipped with single excitation beam. This versatile and easily applicable method has several advantages over any nonflow cytometric (i.e., spectrofluorimetric) energy transfer measurements on cell surfaces: (1) The labeled ligands can be applied in excess, without washing, thereby enahling the investigation of relatively labile receptor‐ligand complexes. (2) Contributions of signals from cell debris, from cell aggregates, or from nonviable cells can be avoided by gating the data collection on the light scatter signal. (3) The heterogeneity of the cell population with respect to the proximity of the labeled binding sites can be studied. (4) In the cases of homologous ligands or of ligands binding to the same molecule but at different epitopes, the determination of fluorescence resonance energy transfer efficiency values can be carried out on a cell‐by‐cell basis, offering data on intramolecular conformational changes.
This modified FCET method enabled us to demonstrate the uniform density of glycoproteins, specific for Con A binding, in the plasma membrane of normal and Gross virus leukemic mouse cells of different sizes. The utility of this procedure has also been demonstrated by using the mean fluorescence intensities of the distribution curves in the calculation of the fluorescence energy transfer efficiency.
Flow cytometry has recently become a choice technique for the quantitative analysis of apoptosis. Monoparametric DNA analysis usually allows identification of apoptotic cells as a “subdiploid” peak. Progression through apoptosis leads to chromatin condensation, nuclear fragmentation and eventually to cell disruption. Thus, a major problem for the flow cytometric analysis of apoptotic populations is discrimination between debris and apoptotic cells. Here we demonstrate that the best parameter on which to make such a distinction is the DNA content, no matter what type of cell is studied. In contrast, discrimination between apoptotic, non‐apoptotic cells, and debris is possible on the basis of scattering signals only in few selected cases, depending on the morphology of the intact cells. © 1993 Wiley‐Liss, Inc.
Multiparameter flow cytometry and cell sorting were used to examine the process of apoptosis after activation of murine resting T cells with immobilized anti‐CD3. Activated T cells treated with Hoechst 33342 (HO‐33342) and analyzed by flow cytometry showed two major cell populations of high and low fluorescence. These populations were sorted and the DNA extracted and subjected to electrophoresis. Electrophoresis of DNA extracted from T cells showing a low level of HO‐33342 fluorescence (HO‐Low) resulted in a typical ladder pattern characteristic of internucleosomal DNA degradation associated with apoptosis, whereas the cellular DNA of the cells showing a high level of fluorescence (HO‐High) showed a narrow high molecular weight band. Multiparameter analysis further indicated that cells with HO‐High characteristics possessed corresponding high‐FSC/low‐SSC properties, whereas HO‐Low cells formed a cluster of low‐FSC/high‐SSC cells. Analysis of the DNA extracted from cells sorted on the basis of scatter properties alone confirmed that the low‐FSC/high‐SSC population contained the apoptotic cells and that the high‐FSC/low‐SSC population was comprised of viable cells. This methodology allowed us to determine the percentage of apoptotic cells following anti‐CD3 activation at various time points and to discriminate them from those in cell cycle. We could further quantitate the number of apoptotic versus viable CD4+ and CD8+ cells in the cell cycle. © 1993 Wiley‐Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.
A method was developed to measure the absolute lymphocyte count (ALC) of whole blood using the Spectrum III automated flow cytometer. Ninety‐nine samples of human peripheral blood were analysed on the Spectrum and the Coulter Counter S Plus II, to allow for comparison of the two machines. Regression analysis was used to test the extent of agreement between the sets of measurements on the two machines. The results demonstrated that the slope of the regression line was not significantly different from one, indicating a high level of correlation between Spectrum and Coulter ALC's. However, the mean difference between Coulter and Spectrum ALC's was not equal to zero, with the Spectrum giving counts approximately 10% lower than those of the Coulter machine. This is attributed to the different ways by which the two machines define a lymphocyte, the Spectrum III by two parameters of light scatter and the Coulter S Plus II by the single parameter of cell volume.
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