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Biomedical subjects

Stephen P Perfetto

Publications and source records attributed to Stephen P Perfetto.

12 recordsLinked to original sources
PubMed2007

Increased immunofluorescence sensitivity using 532 nm laser excitation.

OBJECTIVE: We evaluated the use of a high power, diode pulsed solid-state laser emitting 532 nm light for immunofluorescence applications. We compared the sensitivity and utility of this laser with the standard 488 nm excitation. METHODS: A flow cytometer was equipped with both a 488 nm and a 532 nm laser; fluorescence emissions from each laser were collected using the same filters and the same detector system. Cells or compensation beads (e.g. latex beads coated with anti-kappa antibodies) were stained with monoclonal antibodies conjugated to phycoerythrin (PE) as well as the PE tandem dyes TRPE, Cy5PE, Cy5.5PE, and Cy7PE. The sensitivity of detection of these reagents as well as those in heavily compensated channels was quantified by measuring the spreading error for a primary detector into a secondary detector. RESULTS: Measurement of the fluorescence emission of PE and PE-tandem dyes was considerably more sensitive when using 532 nm excitation (150 mW) as compared with 488 nm excitation (20 mW). In addition, as the absolute number of photoelectrons collected was greater, there was less measurement-error-induced spread into the compensated channels. As an example, when comparing the spreading error of PE labeled cells into the TRPE detector, the green laser was found to be 15-fold more sensitive as compared with the blue laser. In addition, the blue laser produced more autofluoresent signal from cells as compared with the green laser. Together, these advantages of the 532 nm excitation line provides for a significantly improved detection of immunofluorescence staining.

Antibodies, Monoclonal↗
PubMed2006

Quantum dot semiconductor nanocrystals for immunophenotyping by polychromatic flow cytometry.

Immune responses arise from a wide variety of cells expressing unique combinations of multiple cell-surface proteins. Detailed characterization is hampered, however, by limitations in available probes and instrumentation. Here, we use the unique spectral properties of semiconductor nanocrystals (quantum dots) to extend the capabilities of polychromatic flow cytometry to resolve 17 fluorescence emissions. We show the need for this power by analyzing, in detail, the phenotype of multiple antigen-specific T-cell populations, revealing variations within complex phenotypic patterns that would otherwise remain obscure. For example, T cells specific for distinct epitopes from one pathogen, and even those specific for the same epitope, can have markedly different phenotypes. The technology we describe, encompassing the detection of eight quantum dots in conjunction with conventional fluorophores, should expand the horizons of flow cytometry, as well as our ability to characterize the intricacies of both adaptive and innate cellular immune responses.

CD3 Complex↗
PubMed2006

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

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

Amines↗
PubMed2005

Characterization of subsets of CD4+ memory T cells reveals early branched pathways of T cell differentiation in humans.

The pathways for differentiation of human CD4(+) T cells into functionally distinct subsets of memory cells in vivo are unknown. The identification of these subsets and pathways has clear implications for the design of vaccines and immune-targeted therapies. Here, we show that populations of apparently naive CD4(+) T cells express the chemokine receptors CXCR3 or CCR4 and demonstrate patterns of gene expression and functional responses characteristic of memory cells. The proliferation history and T cell receptor repertoire of these chemokine-receptor(+) cells suggest that they are very early memory CD4(+) T cells that have "rested down" before acquiring the phenotypes described for "central" or "effector" memory T cells. In addition, the chemokine-receptor(+) "naive" populations contain Th1 and Th2 cells, respectively, demonstrating that Th1/Th2 differentiation can occur very early in vivo in the absence of markers conventionally associated with memory cells. We localized ligands for CXCR3 and CCR4 to separate foci in T cell zones of tonsil, suggesting that the chemokine-receptor(+) subsets may be recruited and contribute to segregated, polarized microenvironments within lymphoid organs. Importantly, our data suggest that CD4(+) T cells do not differentiate according to a simple schema from naive --> CD45RO(+) noneffector/central memory --> effector/effector memory cells. Rather, developmental pathways branch early on to yield effector/memory populations that are highly heterogeneous and multifunctional and have the potential to become stable resting cells.

CD4-Positive T-Lymphocytes↗
PubMed2004

Vaccination in humans generates broad T cell cytokine responses.

In recent years, the quantification of T cell responses to pathogens or immunogens has become a common tool in the evaluation of disease pathogenesis or vaccine immunogenicity. Such measurements are usually limited to enumerating IFN-gamma-producing cells after ex vivo stimulation with Ag, but little is known about the phenotype or complete functional repertoire of the Ag-specific cells. We used 12-color flow cytometry to characterize Ag-specific T cells elicited by vaccines or natural infection to determine lineage and differentiation status as well as the capacity to produce four cytokines (IFN-gamma, TNF-alpha, IL-2, and IL-4) and a chemokine (MIP1beta). As expected, responding cells had a typical memory phenotype; however, the cytokine profiles associated with the responses were highly complex. The pattern of cytokine coexpression in response to specific Ags was a skewed subset of the complete repertoire (revealed by polyclonal stimulation). We found significant differences in the patterns of cytokines elicited by vaccination (where IFN-gamma was by far a subdominant response) vs natural infection; in addition, there was fairly significant intersubject variation. Our findings illustrate the limitation of the evaluation of immune responses using single functional measurements (such as IFN-gamma); in fact, it is likely that sensitive evaluation of Ag-specific T cells will require the coordinate measurement of several cytokines. The presence and variability of these complex response profiles introduce the possibility that selective functional expression patterns may provide correlates for vaccine efficacy or disease progression.

AIDS Vaccines↗
PubMed2004

Ontogeny of gamma delta T cells in humans.

T cell receptors consist either of an alpha-chain combined with a beta-chain or a gamma-chain combined with a delta-chain. alphabeta T cells constitute the majority of T cells in human blood throughout life. Flow cytometric analyses presented in this study, which focus on the representation of the developmental (naive and memory) subsets of gammadelta T cells, show by function and phenotype that this lineage contains both naive and memory cells. In addition, we show that the representation of naive T cells is higher among alphabeta than gammadelta T cells in adults and that the low frequency of naive gammadelta T cells in adults reflects ontological differences between the two major gammadelta subsets, which are distinguished by expression of Vdelta1 vs Vdelta2 delta-chains. Vdelta1 cells, which mirror alphabeta cells with respect to naive representation, predominate during fetal and early life, but represent the minority of gammadelta cells in healthy adults. In contrast, Vdelta2 cells, which constitute the majority of adult gammadelta cells, show lower frequencies of naive cells than Vdelta1 early in life and show vanishingly small naive frequencies in adults. In essence, nearly all naive Vdelta2 cells disappear from blood by 1 year of life. Importantly, even in children less than 1 year old, most of the nonnaive Vdelta2 cells stain for perforin and produce IFN-gamma after short-term in vitro stimulation. This represents the earliest immunological maturation of any lymphocyte compartment in humans and most likely indicates the importance of these cells in controlling pathology due to common environmental challenges.

Adult↗
PubMed2004

Viable infectious cell sorting in a BSL-3 facility.

With the increase in demand for high-speed cell sorting of viable infectious and now therapeutic cell samples, safety concerns for the protection of flow cytometer operators have increased. This chapter describes a quick, sensitive, and reproducible procedure to assure sample containment before sorting these samples. This procedure includes aerosol containment, physical barriers, environmental controls, and personal protection. An aerosol management system produces a negative pressure within the sort chamber where aerosols are vacuumed directly into a HEPA filter. Physical barriers include the manufacturer's standard plastic shield and panels. The flow cytometer is contained in a BSL-3 laboratory for maximum environmental control and the operator is protected using a respiratory system. Containment is measured using highly fluorescent Glo-Germ particles under the same conditions as the cell sort but with the sorter adjusted to produce large amounts of aerosols. These aerosols are collected by a vacuum air sampling system for 10 min in three locations onto a glass slide and examined microscopically. With this system in place, aerosol containment can be measured quickly and efficiently, therefore reducing the risk to the operator when sorting viable infectious cells.

Aerosols↗
PubMed2003

Measuring containment of viable infectious cell sorting in high-velocity cell sorters.

BACKGROUND: With the advent of high-speed sorters, aerosols are a considerable safety concern when sorting viable infectious materials. We describe a four-part safety procedure for validating the containment. METHODS: This procedure includes aerosol containment, physical barriers, environmental controls, and personal protection. The Aerosol Management System (AMS) produces a negative pressure within the sort chamber, where aerosols are forced through a HEPA filter. Physical barriers include the manufacturer's standard plastic shield and panels. The flow cytometer was contained within a BSL-3 laboratory for maximum environmental control, and the operator was protected by a respiratory system. Containment was measured by using highly fluorescent Glo-Germ particles under the same conditions as the cell sort. RESULTS: Escaping aerosols were vacuumed for 10 min onto a glass slide and examined. With the AMS active and the cytometer producing the maximum aerosols possible, Glo-Germ particles remained within the sort chamber. Measurements taken directly outside the door averaged fewer than one particle per slide, and those taken at 2 ft away and on top of the sorter were completely negative. CONCLUSIONS: With this monitoring system in place, aerosols can be efficiently measured, thus reducing the risk to the operator while sorting viable infectious cells.

Aerosols↗
PubMed2003

Biosafety concerns for shared flow cytometry core facilities.

Many researchers who need flow cytometry for their projects have neither sufficient funds nor the work volume to justify the purchase of an analytic cytometer or cell sorter. In shared flow cytometry facilities, costs for instrument purchases, cytometer maintenance, and personnel are pooled to provide economic services for a multitude of users when they are required. Owing to the diverse nature of the samples that are submitted to core facilities, the biohazard potential of the samples can vary dramatically. For the safety of facility personnel and users, it is critical that information about hazards contained in the samples be transmitted to instrument operators before flow cytometry experiments are started. During 1999 the former Biosafety Committee of the International Society for Analytical Cytology formulated a framework biosafety questionnaire for shared facilities designed to request information about the hazard potential of experimental samples from investigators who wish to use the facility. In this report we review safety issues that are pertinent to flow cytometry core facilities by discussing the individual components of this biosafety questionnaire.

Animals↗
PubMed2002

High-resolution patterns of meiotic recombination across the human major histocompatibility complex.

Definitive characteristics of meiotic recombination events over large (i.e., >1 Mb) segments of the human genome remain obscure, yet they are essential for establishing the haplotypic structure of the genome and for efficient mapping of complex traits. We present a high-resolution map of recombination at the kilobase level across a 3.3-Mb interval encompassing the major histocompatibility complex (MHC). Genotyping of 20,031 single sperm from 12 individuals resulted in the identification and fine mapping of 325 recombinant chromosomes within genomic intervals as small as 7 kb. Several principal characteristics of recombination in this region were observed: (1) rates of recombination can differ significantly between individuals; (2) intense hot spots of recombination occur at least every 0.8 Mb but are not necessarily evenly spaced; (3) distribution in the location of recombination events can differ significantly among individuals; (4) between hot spots, low levels of recombination occur fairly evenly across 100-kb segments, suggesting the presence of warm spots of recombination; and (5) specific sequence motifs associate significantly with recombination distribution. These data provide a plausible model for recombination patterns of the human genome overall.

Adolescent↗