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F Mandy

Publications and source records attributed to F Mandy.

12 recordsLinked to original sources
PubMed2000

Cytofluorometric methods for assessing absolute numbers of cell subsets in blood. European Working Group on Clinical Cell Analysis.

The enumeration of absolute levels of cells and their subsets in clinical samples is of primary importance in human immunodeficiency virus (HIV)+ individuals (CD4+ T- lymphocyte enumeration), in patients who are candidates for autotransplantation (CD34+ hematopoietic progenitor cells), and in evaluating leukoreduced blood products (residual white blood cells). These measurements share a number of technical options, namely, single- or multiple-color cell staining and logical gating strategies. These can be accomplished using single- or dual-platform counting technologies employing cytometric methods. Dual-platform counting technologies couple the percentage of positive cell subsets obtained by cytometry and the absolute cell count obtained by automated hematology analyzers to derive the absolute value of such subsets. Despite having many conceptual and technical limitations, this approach is traditionally considered as the reference method for absolute cell count enumeration. As a result, the development of single-platform technologies has recently attracted attention with several different technical approaches now being readily available. These single-platform approaches have less sources of variability. A number of reports clearly demonstrate that they provide better coefficients of variation (CVs) in multicenter studies and a lower chance to generate aberrant results. These methods are therefore candidates for the new gold standard for absolute cell assessments. The currently available technical options are discussed in this review together with the results of some cross-comparative studies. Each analytical system has its own specific requirements as far as the dispensing precision steps are concerned. The importance of precision reverse pipetting is emphasized. Issues still under development include the establishment of the critical error ranges, which are different in each test setting, and the applicability of simplified low-cost techniques to be used in countries with limited resources.

Antigens, CD34↗
PubMed2000

Decreased HIV-associated T cell apoptosis by HIV protease inhibitors.

Antiretroviral treatment of patients infected with HIV results in improvements in CD4+ T cell number. Emerging evidence suggests that some of the improvements in CD4+ T cell number that occur in response to protease inhibitor (PI) therapy may not be accounted for solely by enhanced viral suppression, implying that PI may directly affect T cell survival. Since HIV T cell depletion is associated with enhanced apoptosis, we analyzed the effect of PIs on T cell apoptosis. In vitro treatment of peripheral blood lymphocytes (PBLs) from HIV-infected but untreated patients with reverse transcriptase inhibitors (RTIs) does not alter apoptosis, whereas PI treatment rapidly reduces CD4+ and CD8+ T cell apoptosis. In contrast, PI treatment does not alter apoptosis in PBL blasts from HIV-negative patients, or in Jurkat T cells. Consistent with this observation, 8 days of PI therapy in HIV-infected patients does not significantly alter plasma viremia, yet results in significant inhibition of CD4+ and CD8+ T cell apoptosis. The inhibitory effects of PI on apoptosis have implications concerning the treatment of HIV and its pathogenesis.

Apoptosis↗
PubMed1998

Quantitative flow cytometry: inter-laboratory variation.

Quantitative flow cytometry (QFCM) offers a means of standardization within and between flow cytometers. QFCM parameters were set by determining the antibody-binding capacity (ABC) of CD4, CD8, and CD3 cells from 10 normal donors with the use of eight FACScan flow cytometers. QC3 beads and a certified blank bead were used to set up the instruments. Fluorescein isothiocyanate (FITC) conjugated to molecular equivalents of soluble fluorochrome (MESF) microbead standards was used before and after the donor samples were run to ensure that the machines were operating consistently. Lyophilized cells (Cytotrol) were used as a target, to control for antigen expression in the cell preparation. Quantitative Simply Cellular (QSC) beads were used to establish a standard calibration curve for each of the FITC and phycoerythrin antibody conjugates on each of the instruments. Single-parameter fluorescent histograms derived from list-mode files were used to calculate the slope (coefficient of response), intercept (zero channel), number of channels per decade, and ABC or MESF threshold (blank bead). The fluorescence intensity (geometric mean) of the positive and negative donor cell populations was compared with the standard curves, and the ABCs were calculated. The results show consistent instrument performance between laboratories. However, after standardization of CD3, CD4, and CD8 ABCs to microbeads, large variations were noted between donors and laboratories. The source of this variation does not appear to be in the instrumentation but may be due to the lack of an unified set-up protocol, introducing issues of antibody saturation, methods for whole blood lysis and fixation, and the behavior of the microbead standards.

Flow Cytometry↗
PubMed1998

Flow cytometric quantitation of immunofluorescence intensity: problems and perspectives. European Working Group on Clinical Cell Analysis.

Quantitation of immunofluorescence intensity serves to estimate the number of defined molecules expressed on or in cells. Clinical applications of this diagnostic tool are increasing, e.g., aberrant expression of various antigens (Ag) by leukemic blasts or lymphoma cells, intensity of CD38 expression by CD8+ T-lymphocytes to monitor activation status, and intensity of CD62P to detect platelet activation. In this report we discuss the quality-control measures required for quantitation of fluorescence intensity, and we review seven concepts that have been developed to quantify fluorescence intensity during the past 15 years. Initial work addressed the conversion of logarithmic channel numbers into units of relative fluorescence. The design and use of calibration beads labeled with predefined amounts of dye allowed instrument-independent expression of fluorescence intensity in units of molecules of equivalent soluble fluorochrome (MESF). This method was refined by the combined use of such standards with monoclonal antibodies (mAb) conjugated 1:1 with phycoerythrin (PE), allowing translation of fluorescence intensity into numbers of antibodies bound per cell. Alternatively, the use of 1:1 PE-conjugated mAb under the assumption that CD4+ lymphocytes reproducibly bind 50,000 CD4 mAb molecules was proposed to convert units of relative fluorescence intensity into units of antibodies bound per cell. The use of antibody-binding capacity as a surrogate marker for quantification of Ag expression was addressed more directly by the development of antibody-binding standards. The quantitative indirect immunofluorescence assay is based on beads labeled with various amounts of CD5 mAb that calibrate the binding of the secondary antibody in units of antibody-binding capacity. Alternatively, goat anti-mouse-labeled calibration beads have been developed. Published results obtained with the latter calibrators showed an unexpected inaccuracy. The different ways in which calibrators and cells under study bind mAb (i.e., Fab mediated versus Fc mediated) may have contributed to this variation. Recently, the use of stabilized cell populations expressing Ag in a specified range of concentrations has been proposed as an Ag-specific calibration system of mAb binding. We identify several issues on the level of instrumentation, reagents, and cells under study that should be solved to allow standardization of quantitative assessments of immunofluorescence intensity.

Animals↗
PubMed1998

Performance of calibration standards for antigen quantitation with flow cytometry.

In the frame of the activities initiated by the Task Force for Antigen Quantitation of the European Working Group on Clinical Cell Analysis (EWGCCA), an experiment was conducted to evaluate microbead standards used for quantitative flow cytometry (QFCM). An unified window of analysis (UWA) was established on three different instruments (EPICS XL [Coulter Corporation, Miami, FL], FACScan and FACS Calibur [Becton Dickinson, San Jose, CA]) with QC3 microbeads (FCSC, PR). By using this defined fluorescence intensity scale, the performance of several monoclonal antibodies directed to CD3, CD4, and CD8 (conjugated and unconjugated), from three manufacturers (BDIS, Coulter [Immunotech], and DAKO) was tested. In addition, the QIFI system (DAKO) and QuantiBRITE (BDIS), and a method of relative fluorescence intensity (RFI, method of Giorgi), were compared. mAbs reacting with three more antigens, CD16, CD19, and CD38 were tested on the FACScan instrument. Quantitation was carried out using a single batch of cryopreserved peripheral blood leukocytes, and all tests were performed as single color analyses. Significant correlations were observed between the antibody-binding capacity (ABC) values of the same CD antigen measured with various calibrators and with antibodies differing in respect to vendor, labeling and possible epitope recognition. Despite the significant correlations, the ABC values of most monoclonal antibodies differed by 20-40% when determined by the different fluorochrome conjugates and different calibrators. The results of this study indicate that, at the present stage of QFCM consistent ABC values may be attained between laboratories provided that a specific calibration system is used including specific calibrators, reagents, and protocols.

Antibodies, Monoclonal↗
PubMed1998

Impact of unified procedures as implemented in the Canadian Quality Assurance Program for T lymphocyte subset enumeration. Participating Flow Cytometry Laboratories of the Canadian Clinical Trials Network for HIV/AIDS Therapies.

The objective of the Canadian Quality Assurance Program (CQAP) is to provide the most reproducible and accurate T-cell subset enumeration for individuals living with HIV who are enrolled in the Canadian Clinical Trial Network for Human Immunodeficiency Virus (HIV) and Acquired Immune Deficiency Syndrome (AIDS) Therapies (abbreviated as CTN). The Canadian National Laboratory for Analytical Cytology, within the Laboratory Centre for Disease Control, is part of the Health Protection Branch of Health Canada. For the past eight years, the Laboratory for Analytical Cytology has been responsible for delivering a bilingual quality assurance program for CD4 T-cell enumeration. This federal program, which integrates biotechnology transfer with quality assessment, was achieved through the organization of workshops focused on technology transfer and essential skill-building techniques. Two training sessions were conducted for the CTN flow cytometer operators. The first introduced the concept of window of analysis, to demonstrate the practical benefits of unified quantitative fluorescent measurement. As a follow-up to the first workshop, participants performed a series of quantitative assays that monitored the expression of CD69, an early activation marker. This quantitative fluorescence protocol was performed with acceptable inter-laboratory variation using modified commercial kits. The second workshop focused on a absolute count method based on a single platform. Four preserved whole-blood preparations were tested with this approach. The combined effort reduced inter-laboratory variation. The direct impact was monitored as related to the frequency of participation. Over the years, the standard deviation of average accumulated variation decreased dramatically with increased frequency of participation, from 10% to <4%.

Canada↗
PubMed1991

Effect of chronic exposure of PCB (Aroclor 1254) on specific and nonspecific immune parameters in the rhesus (Macaca mulatta) monkey.

The immunomodulatory effects of low-level, chronic polychlorinated biphenyl PCB; (Aroclor 1254) exposure were investigated in female rhesus (Macaca mulatta) monkeys. Five groups of monkeys (initially 16 monkeys/group) were orally administered PCB at levels of 0, 5, 20, 40 or 80 micrograms/kg body wt/day. Tests for immunomodulation were initiated after 55 months of exposure to PCBs. Statistically significant observed immune changes included a dose-related decrease in the anamnestic (IgM and IgG) response to sheep red blood cells. Conversely, the antibody response to pneumococcus antigen did not differ significantly across the test groups. A statistically significant dose-related decrease in lymphoproliferation was noted with increasing doses of PCBs when phytohemagglutinin and Concanavalin A, but not when pokeweed mitogen, were used as mitogens. A trend toward reduced peak chemiluminescence (mV/min) was observed in zymosan-activated peripheral blood monocytes. The time to peak chemiluminescence of phorbol myristate acetate activation was statistically increased in a dose-response fashion. Flow cytometric analysis results of peripheral blood lymphocytes using the markers CD4, CD8, and CD20 were similar across the test groups. The mean percentage levels for the CD2 marker in the treated groups were statistically lower than the mean in the control, while absolute numbers for CD2 were similar across the test groups. Serum hydrocortisone levels did not differ among the test groups. Taken together these results indicate that low-level, chronic PCB exposure alters a number of rhesus monkey immune system components and that these effects may be due to altered T-cell and/or macrophage function. These data may be of use in extrapolating potential human health effects following chronic PCB exposure.

Animals↗
PubMed1983

Assessment of the effect of IgG antibodies to ragweed and rye grass on the IgE antibody disc RAST.

The results of the present study indicate that the IgE disc RAST is susceptible to interference by IgG antibodies directed against the same allergens on the disc. Thus removal of IgG antibodies with protein A-Sepharose caused an enhancement of as much as 66% in IgE RAST binding for six sera from treated ragweed and rye grass allergic patients. Furthermore, such interference was shown to vary for a given patient over a period of two years. The use of an alternate support media, matrex-beads linked with excess of ragweed allergen, eliminated the interference effect. The relationship between IgG antibody levels and the interference effect as well as the clinical significance of these findings is discussed.

Absorption↗