Acquisition - The electronic and software function of collecting data from a cytometer’s sensors, filtering the data, and storing it on the computer.

Allophycocyanin (APC) - A fluorescent protein that can be excited by laser lines from 595 to 647 nm and has maximum fluorescence emission between 640 and 680 nm. APC can be conjugated to antibodies for labeling of cell components.

Amplification - The process of increasing a signal. Electronic signals can be amplified either linearly or logarithmically.

Analog - A type of signal processing in which the output is a continuous function rather than a series of discrete (digital) values.

Analog to Digital Converter (ADC) - A device that converts an analog signal to a digital signal.

Analysis - The software function of numerically and graphically manipulating data to generate statistics.

Antibodies - A class of proteins secreted by sensitized B lymphocytes following contact with an antigen. Antibodies bind specifically to the antigen that induced their formation.

Antigen - Any foreign material that is specifically bound by specific antibody or specific lymphocytes; also used loosely to describe materials used for immunization. Antigens may also be immunogens if they are able to trigger an immune response, or haptens if not.

Bandpass Filter - A filter that passes or transmits radiation of a selected bandwidth centered on a designated wavelength and reflects or rejects radiation outside the bandwidth.

Beam Shaping Optics - Optical devices, usually lenses, used to shape laser beams to enhance intensity of the laser beam or make resolution better.

Beam Splitter - An optical device used to divide a beam into two or more separate beams.

B-cell - Lymphocytes that do not mature in the thymus. B lymphocytes produce antibodies.

Cancer - Diseases in which cells divide and grow abnormally.

Cell Lysates - Material obtained from lysing tissues or cell cultures.

CD4 - An antibody (cluster designation 4) against a glycoprotein predominantly found on the surface of helper T cells.

CD4 Count - A measure of the number of T helper cells per cubic millimeter of blood. It is used to study patients with HIV.

Compensation - Process by which spillover fluorescence is removed from secondary parameters so that fluorescence values for a parameter reflect only the fluorescence of the primary fluoroschrome.

Conjugated Antibody - An antibody bound to biotin or a fluorochrome.

Cuvette (flow cell) - See flow cell.

Cytogenetic - the study of heredity by looking at the structure and function of chromosomes. Cytogenetic techniques used to study chromosomes include fluorescence in situ hybridization (FISH), karyotyping, and polymerase chain reaction (PCR).

Cytokines - Chemicals secreted by cells that affect growth or differentiation of other cells.

Cytometric Bead Array (CBA) - Commonly referred to as a multiplexed bead assay, itis a series of spectrally discrete particles that can be used to capture and quantitate soluble analytes.

Cytotoxic (Cytolytic) T cell - Cell that kills target cells bearing appropriate antigen within the groove of an MHC class I molecule that is identical to that of the T cell.

Deflection Plates - Plates that, when charged, produce an electric field that will deflect charged droplets during sorting. One plate is positively charged and the other is negatively charged.

Detector - A device that responds to a specific stimulus. Photodiodes and photomultiplier tubes are the two types of detectors used in BD cytometers. They convert light signals into electronic signals.

Digital - A type of signal processing in which the signal is first converted to a series of discrete (digital) values. The signal is digitized at a rate much faster than the duration of the signal. The digital representation of the signal is used to compute signal characteristics such as pulse area and to compute relationships such as compensation among different signals.

Diode Lasers - A solid state laser made with material that directly converts electrical energy into laser emission. Examples of diode lasers used in flow cytometers are those emitting at wavelengths of 407 nm and 635 nm.

EPA - Environmental Protection Agency—an agency responsible for providing guidelines and monitoring the proper disposal of hazardous materials.

Event Rate - The rate at which cells or particles are acquired.

FACS - Brand name for BD "Fluorescence Activated Cell Sorter."

Flow Cytometry Standard (FCS) - Standard format for flow cytometer data files.

Filter (optical) - An optical device that blocks the passage of part of the incident light, allowing the rest to pass virtually unchanged.

Flow Cytometer - A system that measures the characteristics of cells or particles as they pass through a laser beam one at a time.

Fow Cell (chamber) - The optical structure within the flow cytometer where the sample stream intersects with the laser beams. The flow cell is designed to hydrodynamically focus the stream, transmit incoming laser light, and exit the scattered and fluorescent light.

Flow Rate - Amount of fluid passing through a point per unit time.

Fluorescein Isothiocyanate (FITC) - A fluorescent dye that can be conjugated to antibodies for cell-surface labeling. FITC emits green light with an emission peak at approximately 520 nm.

Fluorescence - The ability of a molecule to absorb light of one wavelength and emit light at a longer wavelength.

Fluorescent Antibody - An antibody coupled to a fluorescent dye. It can be used in fluorescence microscopy or flow cytometry to detect antigens on cells.

Fluorochrome - A fluorescent dye. A molecule capable of absorbing light energy, then emitting light at a longer wavelength (fluorescence) as it releases this energy.

Forward Scatter (FSC) - Light scattered in the direction of laser propagation as a particle passes through the laser beam. The collection angle over which the light is measured is typically between 0.5° to 10° relative to the laser beam axis.

Gain - Amplification of a signal. Increasing the gain results in a larger output signal for a given input signal.

Gate - A numerical or graphical boundary (region) that defines a subset of data from the cytometer. Gates can be single or multidimensional. You can set gates after data acquisition to analyze the data by subpopulation (logical gate); before or during data acquisition to selectively acquire data (live gate); or to specify the subpopulation you wish to sort (sort gate).

GFP - acronym for green fluorescent protein. The GFP gene encodes a fluorescent protein. The gene and its protein product are used in some flow cytometric applications as a fluorescent tag or marker.

Helper T cells - A class of T cells which help trigger B cells to make antibody against antigens. Helper T cells also help generate cytotoxic T cells.

Hydrodynamic Focusing - The sample fluid is injected into the center of the sheath fluid. As both fluids move through a narrowing channel, the sample core remains in the center of the sheath fluid. This process is known as hydrodynamic focusing.

Immunofluorescence - Fluorescence from fluorescent antibodies attached specifically to antigen sites on a cell.

Immunophenotyping - Method used to identify cell characteristics based on the binding of cells to antibodies.

Isotypes - The class of antibodies that share a constant region in the heavy chain.

Isotype Control - A sample stained with an irrelevant antibody of the same isotype as the antibody used in the test. If the antibody used in the test is conjugated to a fluorochrome, the isotype control antibody should be conjugated with the same fluorochrome and with the same amount of fluorochrome per antibody. Isotype control antibodies are typically specific for an antigen known to not be present on the test cells.

Laser - Light amplification by stimulated emission of radiation (LASER). A light source that is highly directional, monochromatic, coherent, and bright. The emitted light is in one or more narrow spectral bands and, with most lasers, is concentrated in an intense, narrow beam.

Laser Delay - Amount of time between signals from different laser intercepts.

Leucoreduced - Blood products such as platelet packs that have undergone a filtration process to remove as many white blood cells as possible.

Light Scatter - Light is scattered off the particle as the laser beam hits the particles passing through.

Linear Amplifier - The linear amplifier produces a signal output proportional to the input signal amplitude. For example, the linear amplifier has a signal output ranging from 1 to 5 volts as the signal input ranges from 0.01 to 0.05 volts. It is the only type of amplifier in a digital data acquisition system. In analog data acquisition systems, a linear amplifier is useful when acquiring data containing cells that vary over a narrow range of signal intensities.

List-Mode File - An unprocessed data file containing all of the measured parameters for each particle in the sample, as well as information describing the sample.

Logarithmic Amplifier - The logarithmic amplifier produces a signal output proportional to the logarithm of the input signal amplitude. A four-decade log amplifier, for example, has a signal output ranging from 0 to 10 volts as the signal input varies by a factor of 10,000. A log amplifier is useful when acquiring data containing cells that vary over a wide range of signal intensities.

Long-Pass Filter - A filter that allows the transmission of wavelengths that are longer than a specified value.

Leukemia - Cancer of the blood cells in the bone marrow.

Lymphocyte - Small white blood cells found mainly in blood and in lymphoid organs.

Melanoma - Cancer of skin, involving primarily melanocytes.

Monoclonal Antibodies - Laboratory-produced antibodies all having identical molecular structure and specificity

Multiple Melanoma - A cancer of the plasma cell. Plasma cells are antibody-secreting cells that develop from B cells.

NCCLS - National Committee for Clinical Laboratory Standards—a committee that provides a communication forum for the development, promotion, and use of national and international standards. Currently called "Clinical and Labortory Standards Institute."

Nozzle - Device at the end of the internal fluidics of a flow cytometer. Drop formation for sorting occurs after stream has gone through the nozzle. Stream and drop characteristics depend on thenozzle size.

Parameter - A measurement of a cell property that is ascertained as the cell passes through the laser beam. Each parameter is the output of a photomultiplier tube or photodiode measuring fluorescent or scattered light (eg, FSC, SSC, FL1, FL2, FL3, or FL4)

Peripheral Blood Mononuclear Cells (PBMCs) - Whole blood that has been passed through a density gradient removing the granulocytes and red blood cells, leaving primarily lymphocytes and monocytes.

phycoerythrin (PE) - A fluorescent dye that can be conjugated to antibodies for cell-surface labeling. PE emits yellow-orange light with an emission peak at approximately 580 nm.

Peridinin Chlorophyll Protein (PerCP) - A fluorescent dye that can be conjugated to antibodies for cell-surface labeling. PerCP emits red light with an emission peak at approximately 677 nm.

peak - The maximum number of events in a single channel, measured within an analysis gate or marker set. Peak channel refers to the channel number where the peak is located. Peak also refers to the maximum value of a signal pulse.

Phosphorylation - the addition of inorganic phosphate (PO4) to a protein. Enzymatic addition and removal of inorganic phosphate is often a control mechanism for activating and deactivating a protein function.

Photodiode - A solid-state device for measuring light intensity. Like the photomultiplier tube (PMT), a photodiode generates an output current proportional to the incident light intensity. Though smaller and simpler to use than a PMT, it is not as sensitive.

Photomultiplier Tube (PMT) - A device for measuring light intensity. PMTs produce an output current proportional to the intensity of incident light. In some applications, PMTs are sensitive enough to count individual photons of light.

Population - Data subset defined by a gate or interval.

Propidium Iodide (PI) - A fluorochrome that emits red light with a peak emission of approximately 620 nm. PI is widely used for DNA analysis, live/dead counting or discrimination and ploidy determination.

Prostate Cancer - Cancer of cells from the prostate gland.

Pulse - A signal that momentarily changes value. As a particle moves through the laser beam, the resulting fluorescent and scattered light appears as a pulse signal. This signal has a low value as the particle enters and leaves the beam and a peak value when the particle passes the beam center.

Pulse Area - A mathematical integral of a single pulse of a signal; the area under the pulse curve. The pulse area represents the total light emission, and is proportional to the amount of fluorochrome on a particle.

Pulse Height - The peak height of a single pulse of a signal.

Pulse Width - The width of a single pulse of a signal. The pulse width is proportional to the time the particle traverses the beam and is a measurement of particle size, laser beam height, and stream velocity.

Purity - In cell sorting, the number of particles in the collection tube that fit the sort criteria divided by the total number of particles in the collection tube.

Quadrants - Two sets of cursors, representing X and Y axes, to divide a two-dimensional histogram into four regions for analysis.

Resolution - A measure of a cytometer’s ability to distinguish between two populations of particles with differing fluorescent or light scatter intensities.

sample core - The sample fluid surrounded by sheath fluid in a hydrodynamically focused flow cell.

Short-Pass Filter - A filter that allows the transmission of wavelengths that are shorter than a specified value.

Side Scatter (SSC) - Also called 90-degree, orthogonal, right-angle, or wide-angle scatter. It is light scattered by a particle at approximately 90° from the incident laser beam. Intensity of side scattered light is related to the internal structure (granularity) of the particle.

Spectral Overlap - The emission spectra of one fluorochrome overlapping with the emission of another. Spectral overlap occurs when a sample is stained with two or more fluorochromes with overlapping emission spectra.

Threshold - The minumum pulse height above which the signal will be processed.

Vaccination - Immunization against a pathogen using components (proteins, whole organisms) of the pathogen or related species. Originally referred to immunization against smallpox using the less virulent cowpox virus.

Voltage - Measure of electric potential. The voltage applied to a PMT affects its amplification gain.

Yield - For cell sorting, the number of particles in the collection tube times the purity divided by the actual number of particles in the sample tube times the percent target particles.