Cell Membrane: The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.Receptors, Cell Surface: Cell surface proteins that bind signalling molecules external to the cell with high affinity and convert this extracellular event into one or more intracellular signals that alter the behavior of the target cell (From Alberts, Molecular Biology of the Cell, 2nd ed, pp693-5). Cell surface receptors, unlike enzymes, do not chemically alter their ligands.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Antigens, Surface: Antigens on surfaces of cells, including infectious or foreign cells or viruses. They are usually protein-containing groups on cell membranes or walls and may be isolated.Membrane Proteins: Proteins which are found in membranes including cellular and intracellular membranes. They consist of two types, peripheral and integral proteins. They include most membrane-associated enzymes, antigenic proteins, transport proteins, and drug, hormone, and lectin receptors.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Endocytosis: Cellular uptake of extracellular materials within membrane-limited vacuoles or microvesicles. ENDOSOMES play a central role in endocytosis.Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Membrane Glycoproteins: Glycoproteins found on the membrane or surface of cells.Protein Binding: The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.Antibodies, Monoclonal: Antibodies produced by a single clone of cells.Protein Transport: The process of moving proteins from one cellular compartment (including extracellular) to another by various sorting and transport mechanisms such as gated transport, protein translocation, and vesicular transport.Cell Adhesion: Adherence of cells to surfaces or to other cells.Biotinylation: Incorporation of biotinyl groups into molecules.Cricetinae: A subfamily in the family MURIDAE, comprising the hamsters. Four of the more common genera are Cricetus, CRICETULUS; MESOCRICETUS; and PHODOPUS.Transfection: The uptake of naked or purified DNA by CELLS, usually meaning the process as it occurs in eukaryotic cells. It is analogous to bacterial transformation (TRANSFORMATION, BACTERIAL) and both are routinely employed in GENE TRANSFER TECHNIQUES.Flow Cytometry: Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake.CHO Cells: CELL LINE derived from the ovary of the Chinese hamster, Cricetulus griseus (CRICETULUS). The species is a favorite for cytogenetic studies because of its small chromosome number. The cell line has provided model systems for the study of genetic alterations in cultured mammalian cells.Antigens, CD: Differentiation antigens residing on mammalian leukocytes. CD stands for cluster of differentiation, which refers to groups of monoclonal antibodies that show similar reactivity with certain subpopulations of antigens of a particular lineage or differentiation stage. The subpopulations of antigens are also known by the same CD designation.Glycoproteins: Conjugated protein-carbohydrate compounds including mucins, mucoid, and amyloid glycoproteins.Glycosylation: The chemical or biochemical addition of carbohydrate or glycosyl groups to other chemicals, especially peptides or proteins. Glycosyl transferases are used in this biochemical reaction.Fluorescent Antibody Technique: Test for tissue antigen using either a direct method, by conjugation of antibody with fluorescent dye (FLUORESCENT ANTIBODY TECHNIQUE, DIRECT) or an indirect method, by formation of antigen-antibody complex which is then labeled with fluorescein-conjugated anti-immunoglobulin antibody (FLUORESCENT ANTIBODY TECHNIQUE, INDIRECT). The tissue is then examined by fluorescence microscopy.Signal Transduction: The intracellular transfer of information (biological activation/inhibition) through a signal pathway. In each signal transduction system, an activation/inhibition signal from a biologically active molecule (hormone, neurotransmitter) is mediated via the coupling of a receptor/enzyme to a second messenger system or to an ion channel. Signal transduction plays an important role in activating cellular functions, cell differentiation, and cell proliferation. Examples of signal transduction systems are the GAMMA-AMINOBUTYRIC ACID-postsynaptic receptor-calcium ion channel system, the receptor-mediated T-cell activation pathway, and the receptor-mediated activation of phospholipases. Those coupled to membrane depolarization or intracellular release of calcium include the receptor-mediated activation of cytotoxic functions in granulocytes and the synaptic potentiation of protein kinase activation. Some signal transduction pathways may be part of larger signal transduction pathways; for example, protein kinase activation is part of the platelet activation signal pathway.Kinetics: The rate dynamics in chemical or physical systems.Biological Transport: The movement of materials (including biochemical substances and drugs) through a biological system at the cellular level. The transport can be across cell membranes and epithelial layers. It also can occur within intracellular compartments and extracellular compartments.Heparitin Sulfate: A heteropolysaccharide that is similar in structure to HEPARIN. It accumulates in individuals with MUCOPOLYSACCHARIDOSIS.Tumor Cells, Cultured: Cells grown in vitro from neoplastic tissue. If they can be established as a TUMOR CELL LINE, they can be propagated in cell culture indefinitely.Golgi Apparatus: A stack of flattened vesicles that functions in posttranslational processing and sorting of proteins, receiving them from the rough ENDOPLASMIC RETICULUM and directing them to secretory vesicles, LYSOSOMES, or the CELL MEMBRANE. The movement of proteins takes place by transfer vesicles that bud off from the rough endoplasmic reticulum or Golgi apparatus and fuse with the Golgi, lysosomes or cell membrane. (From Glick, Glossary of Biochemistry and Molecular Biology, 1990)Recombinant Fusion Proteins: Recombinant proteins produced by the GENETIC TRANSLATION of fused genes formed by the combination of NUCLEIC ACID REGULATORY SEQUENCES of one or more genes with the protein coding sequences of one or more genes.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Protein Structure, Tertiary: The level of protein structure in which combinations of secondary protein structures (alpha helices, beta sheets, loop regions, and motifs) pack together to form folded shapes called domains. Disulfide bridges between cysteines in two different parts of the polypeptide chain along with other interactions between the chains play a role in the formation and stabilization of tertiary structure. Small proteins usually consist of only one domain but larger proteins may contain a number of domains connected by segments of polypeptide chain which lack regular secondary structure.Receptors, Virus: Specific molecular components of the cell capable of recognizing and interacting with a virus, and which, after binding it, are capable of generating some signal that initiates the chain of events leading to the biological response.Lectins: Proteins that share the common characteristic of binding to carbohydrates. Some ANTIBODIES and carbohydrate-metabolizing proteins (ENZYMES) also bind to carbohydrates, however they are not considered lectins. PLANT LECTINS are carbohydrate-binding proteins that have been primarily identified by their hemagglutinating activity (HEMAGGLUTININS). However, a variety of lectins occur in animal species where they serve diverse array of functions through specific carbohydrate recognition.Microscopy, Fluorescence: Microscopy of specimens stained with fluorescent dye (usually fluorescein isothiocyanate) or of naturally fluorescent materials, which emit light when exposed to ultraviolet or blue light. Immunofluorescence microscopy utilizes antibodies that are labeled with fluorescent dye.Recombinant Proteins: Proteins prepared by recombinant DNA technology.Microscopy, Electron: Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.Receptors, Immunologic: Cell surface molecules on cells of the immune system that specifically bind surface molecules or messenger molecules and trigger changes in the behavior of cells. Although these receptors were first identified in the immune system, many have important functions elsewhere.Molecular Weight: The sum of the weight of all the atoms in a molecule.Ligands: A molecule that binds to another molecule, used especially to refer to a small molecule that binds specifically to a larger molecule, e.g., an antigen binding to an antibody, a hormone or neurotransmitter binding to a receptor, or a substrate or allosteric effector binding to an enzyme. Ligands are also molecules that donate or accept a pair of electrons to form a coordinate covalent bond with the central metal atom of a coordination complex. (From Dorland, 27th ed)Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Cell Adhesion Molecules: Surface ligands, usually glycoproteins, that mediate cell-to-cell adhesion. Their functions include the assembly and interconnection of various vertebrate systems, as well as maintenance of tissue integration, wound healing, morphogenic movements, cellular migrations, and metastasis.Endosomes: Cytoplasmic vesicles formed when COATED VESICLES shed their CLATHRIN coat. Endosomes internalize macromolecules bound by receptors on the cell surface.Heparan Sulfate Proteoglycans: Ubiquitous macromolecules associated with the cell surface and extracellular matrix of a wide range of cells of vertebrate and invertebrate tissues. They are essential cofactors in cell-matrix adhesion processes, in cell-cell recognition systems, and in receptor-growth factor interactions. (From Cancer Metastasis Rev 1996; 15(2): 177-86; Hepatology 1996; 24(3): 524-32)Binding Sites: The parts of a macromolecule that directly participate in its specific combination with another molecule.COS Cells: CELL LINES derived from the CV-1 cell line by transformation with a replication origin defective mutant of SV40 VIRUS, which codes for wild type large T antigen (ANTIGENS, POLYOMAVIRUS TRANSFORMING). They are used for transfection and cloning. (The CV-1 cell line was derived from the kidney of an adult male African green monkey (CERCOPITHECUS AETHIOPS).)Glycosylphosphatidylinositols: Compounds containing carbohydrate or glycosyl groups linked to phosphatidylinositols. They anchor GPI-LINKED PROTEINS or polysaccharides to cell membranes.T-Lymphocytes: Lymphocytes responsible for cell-mediated immunity. Two types have been identified - cytotoxic (T-LYMPHOCYTES, CYTOTOXIC) and helper T-lymphocytes (T-LYMPHOCYTES, HELPER-INDUCER). They are formed when lymphocytes circulate through the THYMUS GLAND and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen.Protein Processing, Post-Translational: Any of various enzymatically catalyzed post-translational modifications of PEPTIDES or PROTEINS in the cell of origin. These modifications include carboxylation; HYDROXYLATION; ACETYLATION; PHOSPHORYLATION; METHYLATION; GLYCOSYLATION; ubiquitination; oxidation; proteolysis; and crosslinking and result in changes in molecular weight and electrophoretic motility.Surface Properties: Characteristics or attributes of the outer boundaries of objects, including molecules.Epitopes: Sites on an antigen that interact with specific antibodies.Endoplasmic Reticulum: A system of cisternae in the CYTOPLASM of many cells. In places the endoplasmic reticulum is continuous with the plasma membrane (CELL MEMBRANE) or outer membrane of the nuclear envelope. If the outer surfaces of the endoplasmic reticulum membranes are coated with ribosomes, the endoplasmic reticulum is said to be rough-surfaced (ENDOPLASMIC RETICULUM, ROUGH); otherwise it is said to be smooth-surfaced (ENDOPLASMIC RETICULUM, SMOOTH). (King & Stansfield, A Dictionary of Genetics, 4th ed)Cercopithecus aethiops: A species of CERCOPITHECUS containing three subspecies: C. tantalus, C. pygerythrus, and C. sabeus. They are found in the forests and savannah of Africa. The African green monkey (C. pygerythrus) is the natural host of SIMIAN IMMUNODEFICIENCY VIRUS and is used in AIDS research.Cell Compartmentation: A partitioning within cells due to the selectively permeable membranes which enclose each of the separate parts, e.g., mitochondria, lysosomes, etc.Microscopy, Confocal: A light microscopic technique in which only a small spot is illuminated and observed at a time. An image is constructed through point-by-point scanning of the field in this manner. Light sources may be conventional or laser, and fluorescence or transmitted observations are possible.Fibroblasts: Connective tissue cells which secrete an extracellular matrix rich in collagen and other macromolecules.Proteoglycans: Glycoproteins which have a very high polysaccharide content.Electrophoresis, Polyacrylamide Gel: Electrophoresis in which a polyacrylamide gel is used as the diffusion medium.Carrier Proteins: Transport proteins that carry specific substances in the blood or across cell membranes.Blotting, Western: Identification of proteins or peptides that have been electrophoretically separated by blot transferring from the electrophoresis gel to strips of nitrocellulose paper, followed by labeling with antibody probes.Fibronectins: Glycoproteins found on the surfaces of cells, particularly in fibrillar structures. The proteins are lost or reduced when these cells undergo viral or chemical transformation. They are highly susceptible to proteolysis and are substrates for activated blood coagulation factor VIII. The forms present in plasma are called cold-insoluble globulins.HeLa Cells: The first continuously cultured human malignant CELL LINE, derived from the cervical carcinoma of Henrietta Lacks. These cells are used for VIRUS CULTIVATION and antitumor drug screening assays.RNA, Messenger: RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.Cytoplasm: The part of a cell that contains the CYTOSOL and small structures excluding the CELL NUCLEUS; MITOCHONDRIA; and large VACUOLES. (Glick, Glossary of Biochemistry and Molecular Biology, 1990)Antigens, Neoplasm: Proteins, glycoprotein, or lipoprotein moieties on surfaces of tumor cells that are usually identified by monoclonal antibodies. Many of these are of either embryonic or viral origin.Cell Differentiation: Progressive restriction of the developmental potential and increasing specialization of function that leads to the formation of specialized cells, tissues, and organs.Neuraminidase: An enzyme that catalyzes the hydrolysis of alpha-2,3, alpha-2,6-, and alpha-2,8-glycosidic linkages (at a decreasing rate, respectively) of terminal sialic residues in oligosaccharides, glycoproteins, glycolipids, colominic acid, and synthetic substrate. (From Enzyme Nomenclature, 1992)Down-Regulation: A negative regulatory effect on physiological processes at the molecular, cellular, or systemic level. At the molecular level, the major regulatory sites include membrane receptors, genes (GENE EXPRESSION REGULATION), mRNAs (RNA, MESSENGER), and proteins.Glycosaminoglycans: Heteropolysaccharides which contain an N-acetylated hexosamine in a characteristic repeating disaccharide unit. The repeating structure of each disaccharide involves alternate 1,4- and 1,3-linkages consisting of either N-acetylglucosamine or N-acetylgalactosamine.Bacterial Adhesion: Physicochemical property of fimbriated (FIMBRIAE, BACTERIAL) and non-fimbriated bacteria of attaching to cells, tissue, and nonbiological surfaces. It is a factor in bacterial colonization and pathogenicity.Cricetulus: A genus of the family Muridae consisting of eleven species. C. migratorius, the grey or Armenian hamster, and C. griseus, the Chinese hamster, are the two species used in biomedical research.Brefeldin A: A fungal metabolite which is a macrocyclic lactone exhibiting a wide range of antibiotic activity.Cell Line, Tumor: A cell line derived from cultured tumor cells.Precipitin Tests: Serologic tests in which a positive reaction manifested by visible CHEMICAL PRECIPITATION occurs when a soluble ANTIGEN reacts with its precipitins, i.e., ANTIBODIES that can form a precipitate.Heparin: A highly acidic mucopolysaccharide formed of equal parts of sulfated D-glucosamine and D-glucuronic acid with sulfaminic bridges. The molecular weight ranges from six to twenty thousand. Heparin occurs in and is obtained from liver, lung, mast cells, etc., of vertebrates. Its function is unknown, but it is used to prevent blood clotting in vivo and vitro, in the form of many different salts.Microscopy, Immunoelectron: Microscopy in which the samples are first stained immunocytochemically and then examined using an electron microscope. Immunoelectron microscopy is used extensively in diagnostic virology as part of very sensitive immunoassays.Antibodies: Immunoglobulin molecules having a specific amino acid sequence by virtue of which they interact only with the ANTIGEN (or a very similar shape) that induced their synthesis in cells of the lymphoid series (especially PLASMA CELLS).Lysosomes: A class of morphologically heterogeneous cytoplasmic particles in animal and plant tissues characterized by their content of hydrolytic enzymes and the structure-linked latency of these enzymes. The intracellular functions of lysosomes depend on their lytic potential. The single unit membrane of the lysosome acts as a barrier between the enzymes enclosed in the lysosome and the external substrate. The activity of the enzymes contained in lysosomes is limited or nil unless the vesicle in which they are enclosed is ruptured. Such rupture is supposed to be under metabolic (hormonal) control. (From Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed)Viral Envelope Proteins: Layers of protein which surround the capsid in animal viruses with tubular nucleocapsids. The envelope consists of an inner layer of lipids and virus specified proteins also called membrane or matrix proteins. The outer layer consists of one or more types of morphological subunits called peplomers which project from the viral envelope; this layer always consists of glycoproteins.Receptors, Transferrin: Membrane glycoproteins found in high concentrations on iron-utilizing cells. They specifically bind iron-bearing transferrin, are endocytosed with its ligand and then returned to the cell surface where transferrin without its iron is released.Syndecans: A family of transmembrane glycoproteins that contain a short cytoplasmic domain, a single-span transmembrane domain, and an extracellular domain with heparin sulfate and CHONDROITIN SULFATE chains. Syndecans interact with a variety of heparin-binding INTERCELLULAR SIGNALING PEPTIDES AND PROTEINS and may play a role in modulating cellular signaling during EMBRYONIC DEVELOPMENT, tumorigenesis, and angiogenesis.Models, Biological: Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.Peptides: Members of the class of compounds composed of AMINO ACIDS joined together by peptide bonds between adjacent amino acids into linear, branched or cyclical structures. OLIGOPEPTIDES are composed of approximately 2-12 amino acids. Polypeptides are composed of approximately 13 or more amino acids. PROTEINS are linear polypeptides that are normally synthesized on RIBOSOMES.Sialic Acids: A group of naturally occurring N-and O-acyl derivatives of the deoxyamino sugar neuraminic acid. They are ubiquitously distributed in many tissues.Mice, Inbred BALB CGene Expression Regulation: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control (induction or repression) of gene action at the level of transcription or translation.Mice, Inbred C57BLCloning, Molecular: The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells.Cell Movement: The movement of cells from one location to another. Distinguish from CYTOKINESIS which is the process of dividing the CYTOPLASM of a cell.PolysaccharidesAntigens, CD44: Acidic sulfated integral membrane glycoproteins expressed in several alternatively spliced and variable glycosylated forms on a wide variety of cell types including mature T-cells, B-cells, medullary thymocytes, granulocytes, macrophages, erythrocytes, and fibroblasts. CD44 antigens are the principle cell surface receptors for hyaluronate and this interaction mediates binding of lymphocytes to high endothelial venules. (From Abbas et al., Cellular and Molecular Immunology, 2d ed, p156)N-Acetylneuraminic Acid: An N-acyl derivative of neuraminic acid. N-acetylneuraminic acid occurs in many polysaccharides, glycoproteins, and glycolipids in animals and bacteria. (From Dorland, 28th ed, p1518)GPI-Linked Proteins: A subclass of lipid-linked proteins that contain a GLYCOSYLPHOSPHATIDYLINOSITOL LINKAGE which holds them to the CELL MEMBRANE.Receptors, Concanavalin A: Glycoprotein moieties on the surfaces of cell membranes that bind concanavalin A selectively; the number and location of the sites depends on the type and condition of the cell.Microscopy, Electron, Scanning: Microscopy in which the object is examined directly by an electron beam scanning the specimen point-by-point. The image is constructed by detecting the products of specimen interactions that are projected above the plane of the sample, such as backscattered electrons. Although SCANNING TRANSMISSION ELECTRON MICROSCOPY also scans the specimen point by point with the electron beam, the image is constructed by detecting the electrons, or their interaction products that are transmitted through the sample plane, so that is a form of TRANSMISSION ELECTRON MICROSCOPY.Epithelial Cells: Cells that line the inner and outer surfaces of the body by forming cellular layers (EPITHELIUM) or masses. Epithelial cells lining the SKIN; the MOUTH; the NOSE; and the ANAL CANAL derive from ectoderm; those lining the RESPIRATORY SYSTEM and the DIGESTIVE SYSTEM derive from endoderm; others (CARDIOVASCULAR SYSTEM and LYMPHATIC SYSTEM) derive from mesoderm. Epithelial cells can be classified mainly by cell shape and function into squamous, glandular and transitional epithelial cells.Gene Expression: The phenotypic manifestation of a gene or genes by the processes of GENETIC TRANSCRIPTION and GENETIC TRANSLATION.Histocompatibility Antigens Class I: Membrane glycoproteins consisting of an alpha subunit and a BETA 2-MICROGLOBULIN beta subunit. In humans, highly polymorphic genes on CHROMOSOME 6 encode the alpha subunits of class I antigens and play an important role in determining the serological specificity of the surface antigen. Class I antigens are found on most nucleated cells and are generally detected by their reactivity with alloantisera. These antigens are recognized during GRAFT REJECTION and restrict cell-mediated lysis of virus-infected cells.Bacterial Proteins: Proteins found in any species of bacterium.Integrins: A family of transmembrane glycoproteins (MEMBRANE GLYCOPROTEINS) consisting of noncovalent heterodimers. They interact with a wide variety of ligands including EXTRACELLULAR MATRIX PROTEINS; COMPLEMENT, and other cells, while their intracellular domains interact with the CYTOSKELETON. The integrins consist of at least three identified families: the cytoadhesin receptors(RECEPTORS, CYTOADHESIN), the leukocyte adhesion receptors (RECEPTORS, LEUKOCYTE ADHESION), and the VERY LATE ANTIGEN RECEPTORS. Each family contains a common beta-subunit (INTEGRIN BETA CHAINS) combined with one or more distinct alpha-subunits (INTEGRIN ALPHA CHAINS). These receptors participate in cell-matrix and cell-cell adhesion in many physiologically important processes, including embryological development; HEMOSTASIS; THROMBOSIS; WOUND HEALING; immune and nonimmune defense mechanisms; and oncogenic transformation.Solubility: The ability of a substance to be dissolved, i.e. to form a solution with another substance. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Immunoblotting: Immunologic method used for detecting or quantifying immunoreactive substances. The substance is identified by first immobilizing it by blotting onto a membrane and then tagging it with labeled antibodies.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Membrane Microdomains: Detergent-insoluble CELL MEMBRANE components. They are enriched in SPHINGOLIPIDS and CHOLESTEROL and clustered with glycosyl-phosphatidylinositol (GPI)-anchored proteins.B-Lymphocytes: Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation.Lymphocyte Activation: Morphologic alteration of small B LYMPHOCYTES or T LYMPHOCYTES in culture into large blast-like cells able to synthesize DNA and RNA and to divide mitotically. It is induced by INTERLEUKINS; MITOGENS such as PHYTOHEMAGGLUTININS, and by specific ANTIGENS. It may also occur in vivo as in GRAFT REJECTION.Extracellular Matrix: A meshwork-like substance found within the extracellular space and in association with the basement membrane of the cell surface. It promotes cellular proliferation and provides a supporting structure to which cells or cell lysates in culture dishes adhere.Binding, Competitive: The interaction of two or more substrates or ligands with the same binding site. The displacement of one by the other is used in quantitative and selective affinity measurements.Sequence Homology, Amino Acid: The degree of similarity between sequences of amino acids. This information is useful for the analyzing genetic relatedness of proteins and species.Cell Wall: The outermost layer of a cell in most PLANTS; BACTERIA; FUNGI; and ALGAE. The cell wall is usually a rigid structure that lies external to the CELL MEMBRANE, and provides a protective barrier against physical or chemical agents.Cell Division: The fission of a CELL. It includes CYTOKINESIS, when the CYTOPLASM of a cell is divided, and CELL NUCLEUS DIVISION.Glycoconjugates: Carbohydrates covalently linked to a nonsugar moiety (lipids or proteins). The major glycoconjugates are glycoproteins, glycopeptides, peptidoglycans, glycolipids, and lipopolysaccharides. (From Biochemical Nomenclature and Related Documents, 2d ed; From Principles of Biochemistry, 2d ed)Oligosaccharides: Carbohydrates consisting of between two (DISACCHARIDES) and ten MONOSACCHARIDES connected by either an alpha- or beta-glycosidic link. They are found throughout nature in both the free and bound form.HEK293 Cells: A cell line generated from human embryonic kidney cells that were transformed with human adenovirus type 5.Peptide Fragments: Partial proteins formed by partial hydrolysis of complete proteins or generated through PROTEIN ENGINEERING techniques.Lymphocytes: White blood cells formed in the body's lymphoid tissue. The nucleus is round or ovoid with coarse, irregularly clumped chromatin while the cytoplasm is typically pale blue with azurophilic (if any) granules. Most lymphocytes can be classified as either T or B (with subpopulations of each), or NATURAL KILLER CELLS.Phosphorylation: The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety.Mutagenesis, Site-Directed: Genetically engineered MUTAGENESIS at a specific site in the DNA molecule that introduces a base substitution, or an insertion or deletion.Epithelium: One or more layers of EPITHELIAL CELLS, supported by the basal lamina, which covers the inner or outer surfaces of the body.Immunohistochemistry: Histochemical localization of immunoreactive substances using labeled antibodies as reagents.Clathrin: The main structural coat protein of COATED VESICLES which play a key role in the intracellular transport between membranous organelles. Each molecule of clathrin consists of three light chains (CLATHRIN LIGHT CHAINS) and three heavy chains (CLATHRIN HEAVY CHAINS) that form a structure called a triskelion. Clathrin also interacts with cytoskeletal proteins.Cell Surface Display Techniques: Techniques utilizing cells that express RECOMBINANT FUSION PROTEINS engineered to translocate through the CELL MEMBRANE and remain attached to the outside of the cell.DNA, Complementary: Single-stranded complementary DNA synthesized from an RNA template by the action of RNA-dependent DNA polymerase. cDNA (i.e., complementary DNA, not circular DNA, not C-DNA) is used in a variety of molecular cloning experiments as well as serving as a specific hybridization probe.Cell Aggregation: The phenomenon by which dissociated cells intermixed in vitro tend to group themselves with cells of their own type.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Antigens, CD4: 55-kDa antigens found on HELPER-INDUCER T-LYMPHOCYTES and on a variety of other immune cell types. CD4 antigens are members of the immunoglobulin supergene family and are implicated as associative recognition elements in MAJOR HISTOCOMPATIBILITY COMPLEX class II-restricted immune responses. On T-lymphocytes they define the helper/inducer subset. CD4 antigens also serve as INTERLEUKIN-15 receptors and bind to the HIV receptors, binding directly to the HIV ENVELOPE PROTEIN GP120.Jurkat Cells: A CELL LINE derived from human T-CELL LEUKEMIA and used to determine the mechanism of differential susceptibility to anti-cancer drugs and radiation.Cell SeparationDimerization: The process by which two molecules of the same chemical composition form a condensation product or polymer.Tunicamycin: An N-acetylglycosamine containing antiviral antibiotic obtained from Streptomyces lysosuperificus. It is also active against some bacteria and fungi, because it inhibits the glucosylation of proteins. Tunicamycin is used as tool in the study of microbial biosynthetic mechanisms.Heparin Lyase: An enzyme of the isomerase class that catalyzes the eliminative cleavage of polysaccharides containing 1,4-linked D-glucuronate or L-iduronate residues and 1,4-alpha-linked 2-sulfoamino-2-deoxy-6-sulfo-D-glucose residues to give oligosaccharides with terminal 4-deoxy-alpha-D-gluc-4-enuronosyl groups at their non-reducing ends. (From Enzyme Nomenclature, 1992) EC The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood MONOCYTES. Main types are PERITONEAL MACROPHAGES; ALVEOLAR MACROPHAGES; HISTIOCYTES; KUPFFER CELLS of the liver; and OSTEOCLASTS. They may further differentiate within chronic inflammatory lesions to EPITHELIOID CELLS or may fuse to form FOREIGN BODY GIANT CELLS or LANGHANS GIANT CELLS. (from The Dictionary of Cell Biology, Lackie and Dow, 3rd ed.)Monocytes: Large, phagocytic mononuclear leukocytes produced in the vertebrate BONE MARROW and released into the BLOOD; contain a large, oval or somewhat indented nucleus surrounded by voluminous cytoplasm and numerous organelles.Amino Acid Motifs: Commonly observed structural components of proteins formed by simple combinations of adjacent secondary structures. A commonly observed structure may be composed of a CONSERVED SEQUENCE which can be represented by a CONSENSUS SEQUENCE.Antibody Specificity: The property of antibodies which enables them to react with some ANTIGENIC DETERMINANTS and not with others. Specificity is dependent on chemical composition, physical forces, and molecular structure at the binding site.Monensin: An antiprotozoal agent produced by Streptomyces cinnamonensis. It exerts its effect during the development of first-generation trophozoites into first-generation schizonts within the intestinal epithelial cells. It does not interfere with hosts' development of acquired immunity to the majority of coccidial species. Monensin is a sodium and proton selective ionophore and is widely used as such in biochemical studies.Antigens, CD29: Integrin beta-1 chains which are expressed as heterodimers that are noncovalently associated with specific alpha-chains of the CD49 family (CD49a-f). CD29 is expressed on resting and activated leukocytes and is a marker for all of the very late activation antigens on cells. (from: Barclay et al., The Leukocyte Antigen FactsBook, 1993, p164)3T3 Cells: Cell lines whose original growing procedure consisted being transferred (T) every 3 days and plated at 300,000 cells per plate (J Cell Biol 17:299-313, 1963). Lines have been developed using several different strains of mice. Tissues are usually fibroblasts derived from mouse embryos but other types and sources have been developed as well. The 3T3 lines are valuable in vitro host systems for oncogenic virus transformation studies, since 3T3 cells possess a high sensitivity to CONTACT INHIBITION.Cytoskeleton: The network of filaments, tubules, and interconnecting filamentous bridges which give shape, structure, and organization to the cytoplasm.Concanavalin A: A MANNOSE/GLUCOSE binding lectin isolated from the jack bean (Canavalia ensiformis). It is a potent mitogen used to stimulate cell proliferation in lymphocytes, primarily T-lymphocyte, cultures.Receptors, Urokinase Plasminogen Activator: An extracellular receptor specific for UROKINASE-TYPE PLASMINOGEN ACTIVATOR. It is attached to the cell membrane via a GLYCOSYLPHOSPHATIDYLINOSITOL LINKAGE and plays a role in the co-localization of urokinase-type plasminogen activator with PLASMINOGEN.Green Fluorescent Proteins: Protein analogs and derivatives of the Aequorea victoria green fluorescent protein that emit light (FLUORESCENCE) when excited with ULTRAVIOLET RAYS. They are used in REPORTER GENES in doing GENETIC TECHNIQUES. Numerous mutants have been made to emit other colors or be sensitive to pH.Rabbits: The species Oryctolagus cuniculus, in the family Leporidae, order LAGOMORPHA. Rabbits are born in burrows, furless, and with eyes and ears closed. In contrast with HARES, rabbits have 22 chromosome pairs.Receptors, Antigen, B-Cell: IMMUNOGLOBULINS on the surface of B-LYMPHOCYTES. Their MESSENGER RNA contains an EXON with a membrane spanning sequence, producing immunoglobulins in the form of type I transmembrane proteins as opposed to secreted immunoglobulins (ANTIBODIES) which do not contain the membrane spanning segment.Endothelium, Vascular: Single pavement layer of cells which line the luminal surface of the entire vascular system and regulate the transport of macromolecules and blood components.DNA Primers: Short sequences (generally about 10 base pairs) of DNA that are complementary to sequences of messenger RNA and allow reverse transcriptases to start copying the adjacent sequences of mRNA. Primers are used extensively in genetic and molecular biology techniques.Metalloendopeptidases: ENDOPEPTIDASES which use a metal such as ZINC in the catalytic mechanism.Syndecan-1: A syndecan that interacts with EXTRACELLULAR MATRIX PROTEINS and plays a role CELL PROLIFERATION and CELL MIGRATION.Kidney: Body organ that filters blood for the secretion of URINE and that regulates ion concentrations.Structure-Activity Relationship: The relationship between the chemical structure of a compound and its biological or pharmacological activity. Compounds are often classed together because they have structural characteristics in common including shape, size, stereochemical arrangement, and distribution of functional groups.Immunoprecipitation: The aggregation of soluble ANTIGENS with ANTIBODIES, alone or with antibody binding factors such as ANTI-ANTIBODIES or STAPHYLOCOCCAL PROTEIN A, into complexes large enough to fall out of solution.Temperature: The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.Protein Conformation: The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).Immune Sera: Serum that contains antibodies. It is obtained from an animal that has been immunized either by ANTIGEN injection or infection with microorganisms containing the antigen.Receptors, Mitogen: Glycoprotein molecules on the surface of B- and T-lymphocytes, that react with molecules of antilymphocyte sera, lectins, and other agents which induce blast transformation of lymphocytes.Laminin: Large, noncollagenous glycoprotein with antigenic properties. It is localized in the basement membrane lamina lucida and functions to bind epithelial cells to the basement membrane. Evidence suggests that the protein plays a role in tumor invasion.Glycoside HydrolasesCell Line, Transformed: Eukaryotic cell line obtained in a quiescent or stationary phase which undergoes conversion to a state of unregulated growth in culture, resembling an in vitro tumor. It occurs spontaneously or through interaction with viruses, oncogenes, radiation, or drugs/chemicals.Up-Regulation: A positive regulatory effect on physiological processes at the molecular, cellular, or systemic level. At the molecular level, the major regulatory sites include membrane receptors, genes (GENE EXPRESSION REGULATION), mRNAs (RNA, MESSENGER), and proteins.Dogs: The domestic dog, Canis familiaris, comprising about 400 breeds, of the carnivore family CANIDAE. They are worldwide in distribution and live in association with people. (Walker's Mammals of the World, 5th ed, p1065)Subcellular Fractions: Components of a cell produced by various separation techniques which, though they disrupt the delicate anatomy of a cell, preserve the structure and physiology of its functioning constituents for biochemical and ultrastructural analysis. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p163)Transferrin: An iron-binding beta1-globulin that is synthesized in the LIVER and secreted into the blood. It plays a central role in the transport of IRON throughout the circulation. A variety of transferrin isoforms exist in humans, including some that are considered markers for specific disease states.Antigens, Differentiation, B-Lymphocyte: Membrane antigens associated with maturation stages of B-lymphocytes, often expressed in tumors of B-cell origin.Coated Pits, Cell-Membrane: Specialized regions of the cell membrane composed of pits coated with a bristle covering made of the protein CLATHRIN. These pits are the entry route for macromolecules bound by cell surface receptors. The pits are then internalized into the cytoplasm to form the COATED VESICLES.Virus Attachment: The binding of virus particles to receptors on the host cell surface. For enveloped viruses, the virion ligand is usually a surface glycoprotein as is the cellular receptor. For non-enveloped viruses, the virus CAPSID serves as the ligand.Cell Fusion: Fusion of somatic cells in vitro or in vivo, which results in somatic cell hybridization.Virus Internalization: The entering of cells by viruses following VIRUS ATTACHMENT. This is achieved by ENDOCYTOSIS, by direct MEMBRANE FUSION of the viral membrane with the CELL MEMBRANE, or by translocation of the whole virus across the cell membrane.Exocytosis: Cellular release of material within membrane-limited vesicles by fusion of the vesicles with the CELL MEMBRANE.Bacterial Outer Membrane Proteins: Proteins isolated from the outer membrane of Gram-negative bacteria.Antigen-Antibody Reactions: The processes triggered by interactions of ANTIBODIES with their ANTIGENS.Cattle: Domesticated bovine animals of the genus Bos, usually kept on a farm or ranch and used for the production of meat or dairy products or for heavy labor.Asialoglycoproteins: Endogenous glycoproteins from which SIALIC ACID has been removed by the action of sialidases. They bind tightly to the ASIALOGLYCOPROTEIN RECEPTOR which is located on hepatocyte plasma membranes. After internalization by adsorptive ENDOCYTOSIS they are delivered to LYSOSOMES for degradation. Therefore receptor-mediated clearance of asialoglycoproteins is an important aspect of the turnover of plasma glycoproteins. They are elevated in serum of patients with HEPATIC CIRRHOSIS or HEPATITIS.Antigens, Differentiation: Antigens expressed primarily on the membranes of living cells during sequential stages of maturation and differentiation. As immunologic markers they have high organ and tissue specificity and are useful as probes in studies of normal cell development as well as neoplastic transformation.Trypsin: A serine endopeptidase that is formed from TRYPSINOGEN in the pancreas. It is converted into its active form by ENTEROPEPTIDASE in the small intestine. It catalyzes hydrolysis of the carboxyl group of either arginine or lysine. EC The clumping together of suspended material resulting from the action of AGGLUTININS.Binding Sites, Antibody: Local surface sites on antibodies which react with antigen determinant sites on antigens (EPITOPES.) They are formed from parts of the variable regions of FAB FRAGMENTS.Cell Polarity: Orientation of intracellular structures especially with respect to the apical and basolateral domains of the plasma membrane. Polarized cells must direct proteins from the Golgi apparatus to the appropriate domain since tight junctions prevent proteins from diffusing between the two domains.trans-Golgi Network: A network of membrane compartments, located at the cytoplasmic side of the GOLGI APPARATUS, where proteins and lipids are sorted for transport to various locations in the cell or cell membrane.Oligopeptides: Peptides composed of between two and twelve amino acids.Apoptosis: One of the mechanisms by which CELL DEATH occurs (compare with NECROSIS and AUTOPHAGOCYTOSIS). Apoptosis is the mechanism responsible for the physiological deletion of cells and appears to be intrinsically programmed. It is characterized by distinctive morphologic changes in the nucleus and cytoplasm, chromatin cleavage at regularly spaced sites, and the endonucleolytic cleavage of genomic DNA; (DNA FRAGMENTATION); at internucleosomal sites. This mode of cell death serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth.Enzyme Activation: Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1, activation by ions (activators); 2, activation by cofactors (coenzymes); and 3, conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme.Neoplasm Proteins: Proteins whose abnormal expression (gain or loss) are associated with the development, growth, or progression of NEOPLASMS. Some neoplasm proteins are tumor antigens (ANTIGENS, NEOPLASM), i.e. they induce an immune reaction to their tumor. Many neoplasm proteins have been characterized and are used as tumor markers (BIOMARKERS, TUMOR) when they are detectable in cells and body fluids as monitors for the presence or growth of tumors. Abnormal expression of ONCOGENE PROTEINS is involved in neoplastic transformation, whereas the loss of expression of TUMOR SUPPRESSOR PROTEINS is involved with the loss of growth control and progression of the neoplasm.Receptors, Fibronectin: Specific cell surface receptors which bind to FIBRONECTINS. Studies have shown that these receptors function in certain types of adhesive contact as well as playing a major role in matrix assembly. These receptors include the traditional fibronectin receptor, also called INTEGRIN ALPHA5BETA1 and several other integrins.Gangliosides: A subclass of ACIDIC GLYCOSPHINGOLIPIDS. They contain one or more sialic acid (N-ACETYLNEURAMINIC ACID) residues. Using the Svennerholm system of abbrevations, gangliosides are designated G for ganglioside, plus subscript M, D, or T for mono-, di-, or trisialo, respectively, the subscript letter being followed by a subscript arabic numeral to indicated sequence of migration in thin-layer chromatograms. (From Oxford Dictionary of Biochemistry and Molecular Biology, 1997)Glucose Transporter Type 4: A glucose transport protein found in mature MUSCLE CELLS and ADIPOCYTES. It promotes transport of glucose from the BLOOD into target TISSUES. The inactive form of the protein is localized in CYTOPLASMIC VESICLES. In response to INSULIN, it is translocated to the PLASMA MEMBRANE where it facilitates glucose uptake.Chromatography, Affinity: A chromatographic technique that utilizes the ability of biological molecules to bind to certain ligands specifically and reversibly. It is used in protein biochemistry. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Biotin: A water-soluble, enzyme co-factor present in minute amounts in every living cell. It occurs mainly bound to proteins or polypeptides and is abundant in liver, kidney, pancreas, yeast, and milk.Mice, Knockout: Strains of mice in which certain GENES of their GENOMES have been disrupted, or "knocked-out". To produce knockouts, using RECOMBINANT DNA technology, the normal DNA sequence of the gene being studied is altered to prevent synthesis of a normal gene product. Cloned cells in which this DNA alteration is successful are then injected into mouse EMBRYOS to produce chimeric mice. The chimeric mice are then bred to yield a strain in which all the cells of the mouse contain the disrupted gene. Knockout mice are used as EXPERIMENTAL ANIMAL MODELS for diseases (DISEASE MODELS, ANIMAL) and to clarify the functions of the genes.Antigens, CD55: GPI-linked membrane proteins broadly distributed among hematopoietic and non-hematopoietic cells. CD55 prevents the assembly of C3 CONVERTASE or accelerates the disassembly of preformed convertase, thus blocking the formation of the membrane attack complex.beta 2-Microglobulin: An 11-kDa protein associated with the outer membrane of many cells including lymphocytes. It is the small subunit of the MHC class I molecule. Association with beta 2-microglobulin is generally required for the transport of class I heavy chains from the endoplasmic reticulum to the cell surface. Beta 2-microglobulin is present in small amounts in serum, csf, and urine of normal people, and to a much greater degree in the urine and plasma of patients with tubular proteinemia, renal failure, or kidney transplants.Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.Carbohydrate Sequence: The sequence of carbohydrates within POLYSACCHARIDES; GLYCOPROTEINS; and GLYCOLIPIDS.L Cells (Cell Line): A cultured line of C3H mouse FIBROBLASTS that do not adhere to one another and do not express CADHERINS.Histocompatibility Antigens Class II: Large, transmembrane, non-covalently linked glycoproteins (alpha and beta). Both chains can be polymorphic although there is more structural variation in the beta chains. The class II antigens in humans are called HLA-D ANTIGENS and are coded by a gene on chromosome 6. In mice, two genes named IA and IE on chromosome 17 code for the H-2 antigens. The antigens are found on B-lymphocytes, macrophages, epidermal cells, and sperm and are thought to mediate the competence of and cellular cooperation in the immune response. The term IA antigens used to refer only to the proteins encoded by the IA genes in the mouse, but is now used as a generic term for any class II histocompatibility antigen.Calcium: A basic element found in nearly all organized tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.Chick Embryo: The developmental entity of a fertilized chicken egg (ZYGOTE). The developmental process begins about 24 h before the egg is laid at the BLASTODISC, a small whitish spot on the surface of the EGG YOLK. After 21 days of incubation, the embryo is fully developed before hatching.Phosphatidylinositol Diacylglycerol-Lyase: A phosphorus-oxygen lyase found primarily in BACTERIA. The enzyme catalyzes the cleavage of a phosphoester linkage in 1-phosphatidyl-1D-myo-inositol to form 1D-myo-inositol 1,2-cyclic phosphate and diacylglycerol. The enzyme was formerly classified as a phosphoric diester hydrolase (EC and is often referred to as a TYPE C PHOSPHOLIPASES. However it is now known that a cyclic phosphate is the final product of this enzyme and that water does not enter into the reaction.Membrane Fusion: The adherence and merging of cell membranes, intracellular membranes, or artificial membranes to each other or to viruses, parasites, or interstitial particles through a variety of chemical and physical processes.Carbohydrates: The largest class of organic compounds, including STARCH; GLYCOGEN; CELLULOSE; POLYSACCHARIDES; and simple MONOSACCHARIDES. Carbohydrates are composed of carbon, hydrogen, and oxygen in a ratio of Cn(H2O)n.Iodine Radioisotopes: Unstable isotopes of iodine that decay or disintegrate emitting radiation. I atoms with atomic weights 117-139, except I 127, are radioactive iodine isotopes.Clone Cells: A group of genetically identical cells all descended from a single common ancestral cell by mitosis in eukaryotes or by binary fission in prokaryotes. Clone cells also include populations of recombinant DNA molecules all carrying the same inserted sequence. (From King & Stansfield, Dictionary of Genetics, 4th ed)