Adaptive Immunity: Protection from an infectious disease agent that is mediated by B- and T- LYMPHOCYTES following exposure to specific antigen, and characterized by IMMUNOLOGIC MEMORY. It can result from either previous infection with that agent or vaccination (IMMUNITY, ACTIVE), or transfer of antibody or lymphocytes from an immune donor (IMMUNIZATION, PASSIVE).Immunity, Innate: The capacity of a normal organism to remain unaffected by microorganisms and their toxins. It results from the presence of naturally occurring ANTI-INFECTIVE AGENTS, constitutional factors such as BODY TEMPERATURE and immediate acting immune cells such as NATURAL KILLER CELLS.Immunity: Nonsusceptibility to the invasive or pathogenic effects of foreign microorganisms or to the toxic effect of antigenic substances.Immunity, Cellular: Manifestations of the immune response which are mediated by antigen-sensitized T-lymphocytes via lymphokines or direct cytotoxicity. This takes place in the absence of circulating antibody or where antibody plays a subordinate role.Immunity, Active: Resistance to a disease agent resulting from the production of specific antibodies by the host, either after exposure to the disease or after vaccination.Dendritic Cells: Specialized cells of the hematopoietic system that have branch-like extensions. They are found throughout the lymphatic system, and in non-lymphoid tissues such as SKIN and the epithelia of the intestinal, respiratory, and reproductive tracts. They trap and process ANTIGENS, and present them to T-CELLS, thereby stimulating CELL-MEDIATED IMMUNITY. They are different from the non-hematopoietic FOLLICULAR DENDRITIC CELLS, which have a similar morphology and immune system function, but with respect to humoral immunity (ANTIBODY PRODUCTION).Mice, Inbred C57BLT-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.Immunity, Mucosal: Nonsusceptibility to the pathogenic effects of foreign microorganisms or antigenic substances as a result of antibody secretions of the mucous membranes. Mucosal epithelia in the gastrointestinal, respiratory, and reproductive tracts produce a form of IgA (IMMUNOGLOBULIN A, SECRETORY) that serves to protect these ports of entry into the body.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.Toll-Like Receptors: A family of pattern recognition receptors characterized by an extracellular leucine-rich domain and a cytoplasmic domain that share homology with the INTERLEUKIN 1 RECEPTOR and the DROSOPHILA toll protein. Following pathogen recognition, toll-like receptors recruit and activate a variety of SIGNAL TRANSDUCING ADAPTOR PROTEINS.Cytokines: Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner.Mice, Inbred BALB CAdaptation, Physiological: The non-genetic biological changes of an organism in response to challenges in its ENVIRONMENT.Immunity, Humoral: Antibody-mediated immune response. Humoral immunity is brought about by ANTIBODY FORMATION, resulting from TH2 CELLS activating B-LYMPHOCYTES, followed by COMPLEMENT ACTIVATION.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.Interferon-gamma: The major interferon produced by mitogenically or antigenically stimulated LYMPHOCYTES. It is structurally different from TYPE I INTERFERON and its major activity is immunoregulation. It has been implicated in the expression of CLASS II HISTOCOMPATIBILITY ANTIGENS in cells that do not normally produce them, leading to AUTOIMMUNE DISEASES.CD8-Positive T-Lymphocytes: A critical subpopulation of regulatory T-lymphocytes involved in MHC Class I-restricted interactions. They include both cytotoxic T-lymphocytes (T-LYMPHOCYTES, CYTOTOXIC) and CD8+ suppressor T-lymphocytes.CD4-Positive T-Lymphocytes: A critical subpopulation of T-lymphocytes involved in the induction of most immunological functions. The HIV virus has selective tropism for the T4 cell which expresses the CD4 phenotypic marker, a receptor for HIV. In fact, the key element in the profound immunosuppression seen in HIV infection is the depletion of this subset of T-lymphocytes.Killer Cells, Natural: Bone marrow-derived lymphocytes that possess cytotoxic properties, classically directed against transformed and virus-infected cells. Unlike T CELLS; and B CELLS; NK CELLS are not antigen specific. The cytotoxicity of natural killer cells is determined by the collective signaling of an array of inhibitory and stimulatory CELL SURFACE RECEPTORS. A subset of T-LYMPHOCYTES referred to as NATURAL KILLER T CELLS shares some of the properties of this cell type.Immune System: The body's defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components.Models, Immunological: Theoretical representations that simulate the behavior or activity of immune system, processes, or phenomena. They include the use of mathematical equations, computers, and other electrical equipment.Adaptation, Biological: Changes in biological features that help an organism cope with its ENVIRONMENT. These changes include physiological (ADAPTATION, PHYSIOLOGICAL), phenotypic and genetic changes.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.Receptors, Pattern Recognition: A large family of cell surface receptors that bind conserved molecular structures (PAMPS) present in pathogens. They play important roles in host defense by mediating cellular responses to pathogens.Antigen Presentation: The process by which antigen is presented to lymphocytes in a form they can recognize. This is performed by antigen presenting cells (APCs). Some antigens require processing before they can be recognized. Antigen processing consists of ingestion and partial digestion of the antigen by the APC, followed by presentation of fragments on the cell surface. (From Rosen et al., Dictionary of Immunology, 1989)Th1 Cells: Subset of helper-inducer T-lymphocytes which synthesize and secrete interleukin-2, gamma-interferon, and interleukin-12. Due to their ability to kill antigen-presenting cells and their lymphokine-mediated effector activity, Th1 cells are associated with vigorous delayed-type hypersensitivity reactions.Adjuvants, Immunologic: Substances that augment, stimulate, activate, potentiate, or modulate the immune response at either the cellular or humoral level. The classical agents (Freund's adjuvant, BCG, Corynebacterium parvum, et al.) contain bacterial antigens. Some are endogenous (e.g., histamine, interferon, transfer factor, tuftsin, interleukin-1). Their mode of action is either non-specific, resulting in increased immune responsiveness to a wide variety of antigens, or antigen-specific, i.e., affecting a restricted type of immune response to a narrow group of antigens. The therapeutic efficacy of many biological response modifiers is related to their antigen-specific immunoadjuvanticity.Plant Immunity: The inherent or induced capacity of plants to withstand or ward off biological attack by pathogens.Spleen: An encapsulated lymphatic organ through which venous blood filters.Inflammation: A pathological process characterized by injury or destruction of tissues caused by a variety of cytologic and chemical reactions. It is usually manifested by typical signs of pain, heat, redness, swelling, and loss of function.Interleukin-12: A heterodimeric cytokine that plays a role in innate and adaptive immune responses. Interleukin-12 is a 70 kDa protein that is composed of covalently linked 40 kDa and 35 kDa subunits. It is produced by DENDRITIC CELLS; MACROPHAGES and a variety of other immune cells and plays a role in the stimulation of INTERFERON-GAMMA production by T-LYMPHOCYTES and NATURAL KILLER CELLS.Immunologic Memory: The altered state of immunologic responsiveness resulting from initial contact with antigen, which enables the individual to produce antibodies more rapidly and in greater quantity in response to secondary antigenic stimulus.Macrophages: 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.)Myeloid Differentiation Factor 88: An intracellular signaling adaptor protein that plays a role in TOLL-LIKE RECEPTOR and INTERLEUKIN 1 RECEPTORS signal transduction. It forms a signaling complex with the activated cell surface receptors and members of the IRAK KINASES.Immune Evasion: Methods used by pathogenic organisms to evade a host's immune system.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.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.Antibody Formation: The production of ANTIBODIES by proliferating and differentiated B-LYMPHOCYTES under stimulation by ANTIGENS.Disease Models, Animal: Naturally occurring or experimentally induced animal diseases with pathological processes sufficiently similar to those of human diseases. They are used as study models for human diseases.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.Immunity, Maternally-Acquired: Resistance to a disease-causing agent induced by the introduction of maternal immunity into the fetus by transplacental transfer or into the neonate through colostrum and milk.T-Lymphocyte Subsets: A classification of T-lymphocytes, especially into helper/inducer, suppressor/effector, and cytotoxic subsets, based on structurally or functionally different populations of cells.Host-Pathogen Interactions: The interactions between a host and a pathogen, usually resulting in disease.Immune Tolerance: The specific failure of a normally responsive individual to make an immune response to a known antigen. It results from previous contact with the antigen by an immunologically immature individual (fetus or neonate) or by an adult exposed to extreme high-dose or low-dose antigen, or by exposure to radiation, antimetabolites, antilymphocytic serum, etc.Vaccines: Suspensions of killed or attenuated microorganisms (bacteria, viruses, fungi, protozoa), antigenic proteins, synthetic constructs, or other bio-molecular derivatives, administered for the prevention, amelioration, or treatment of infectious and other diseases.Toll-Like Receptor 4: A pattern recognition receptor that interacts with LYMPHOCYTE ANTIGEN 96 and LIPOPOLYSACCHARIDES. It mediates cellular responses to GRAM-NEGATIVE BACTERIA.Vaccination: Administration of vaccines to stimulate the host's immune response. This includes any preparation intended for active immunological prophylaxis.Immunomodulation: Alteration of the immune system or of an immune response by agents that activate or suppress its function. This can include IMMUNIZATION or administration of immunomodulatory drugs. Immunomodulation can also encompass non-therapeutic alteration of the immune system effected by endogenous or exogenous substances.Virus Diseases: A general term for diseases produced by viruses.Mice, Transgenic: Laboratory mice that have been produced from a genetically manipulated EGG or EMBRYO, MAMMALIAN.Toll-Like Receptor 2: A pattern recognition receptor that forms heterodimers with other TOLL-LIKE RECEPTORS. It interacts with multiple ligands including PEPTIDOGLYCAN, bacterial LIPOPROTEINS, lipoarabinomannan, and a variety of PORINS.Immunoglobulin G: The major immunoglobulin isotype class in normal human serum. There are several isotype subclasses of IgG, for example, IgG1, IgG2A, and IgG2B.Th2 Cells: Subset of helper-inducer T-lymphocytes which synthesize and secrete the interleukins IL-4, IL-5, IL-6, and IL-10. These cytokines influence B-cell development and antibody production as well as augmenting humoral responses.Listeriosis: Infections with bacteria of the genus LISTERIA.Interleukin-17: A proinflammatory cytokine produced primarily by T-LYMPHOCYTES or their precursors. Several subtypes of interleukin-17 have been identified, each of which is a product of a unique gene.Genes, RAG-1: Genes involved in activating the enzyme VDJ recombinase. RAG-1 is located on chromosome 11 in humans (chromosome 2 in mice) and is expressed exclusively in maturing lymphocytes.Membrane Glycoproteins: Glycoproteins found on the membrane or surface of cells.Cell Differentiation: Progressive restriction of the developmental potential and increasing specialization of function that leads to the formation of specialized cells, tissues, and organs.Adoptive Transfer: Form of passive immunization where previously sensitized immunologic agents (cells or serum) are transferred to non-immune recipients. When transfer of cells is used as a therapy for the treatment of neoplasms, it is called adoptive immunotherapy (IMMUNOTHERAPY, ADOPTIVE).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.Antibodies, Viral: Immunoglobulins produced in response to VIRAL ANTIGENS.Antigens, CD11c: An integrin alpha subunit of approximately 150-kDa molecular weight. It is expressed at high levels on monocytes and combines with CD18 ANTIGEN to form the cell surface receptor INTEGRIN ALPHAXBETA2. The subunit contains a conserved I-domain which is characteristic of several of alpha integrins.Cancer Vaccines: Vaccines or candidate vaccines designed to prevent or treat cancer. Vaccines are produced using the patient's own whole tumor cells as the source of antigens, or using tumor-specific antigens, often recombinantly produced.Antigens: Substances that are recognized by the immune system and induce an immune reaction.Antigen-Presenting Cells: A heterogeneous group of immunocompetent cells that mediate the cellular immune response by processing and presenting antigens to the T-cells. Traditional antigen-presenting cells include MACROPHAGES; DENDRITIC CELLS; LANGERHANS CELLS; and B-LYMPHOCYTES. FOLLICULAR DENDRITIC CELLS are not traditional antigen-presenting cells, but because they hold antigen on their cell surface in the form of IMMUNE COMPLEXES for B-cell recognition they are considered so by some authors.Evolution, Molecular: The process of cumulative change at the level of DNA; RNA; and PROTEINS, over successive generations.Th17 Cells: Subset of helper-effector T-lymphocytes which synthesize and secrete IL-17, IL-17F, and IL-22. These cytokines are involved in host defenses and tissue inflammation in autoimmune diseases.T-Lymphocytes, Regulatory: CD4-positive T cells that inhibit immunopathology or autoimmune disease in vivo. They inhibit the immune response by influencing the activity of other cell types. Regulatory T-cells include naturally occurring CD4+CD25+ cells, IL-10 secreting Tr1 cells, and Th3 cells.Gene 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.Receptors, Antigen: Molecules on the surface of B- and T-lymphocytes that recognize and combine with specific antigens.Interferon Type I: Interferon secreted by leukocytes, fibroblasts, or lymphoblasts in response to viruses or interferon inducers other than mitogens, antigens, or allo-antigens. They include alpha- and beta-interferons (INTERFERON-ALPHA and INTERFERON-BETA).Allergy and Immunology: A medical specialty concerned with the hypersensitivity of the individual to foreign substances and protection from the resultant infection or disorder.Autoimmunity: Process whereby the immune system reacts against the body's own tissues. Autoimmunity may produce or be caused by AUTOIMMUNE DISEASES.Mice, Inbred C3HLung: Either of the pair of organs occupying the cavity of the thorax that effect the aeration of the blood.Biological Evolution: The process of cumulative change over successive generations through which organisms acquire their distinguishing morphological and physiological characteristics.Cytotoxicity, Immunologic: The phenomenon of target cell destruction by immunologically active effector cells. It may be brought about directly by sensitized T-lymphocytes or by lymphoid or myeloid "killer" cells, or it may be mediated by cytotoxic antibody, cytotoxic factor released by lymphoid cells, or complement.Natural Killer T-Cells: A specialized subset of T-LYMPHOCYTES that exhibit features of INNATE IMMUNITY similar to that of NATURAL KILLER CELLS. They are reactive to glycolipids presented in the context of the major histocompatibility complex (MHC) class I-like molecule, CD1D ANTIGEN.Immunity, Herd: The non-susceptibility to infection of a large group of individuals in a population. A variety of factors can be responsible for herd immunity and this gives rise to the different definitions used in the literature. Most commonly, herd immunity refers to the case when, if most of the population is immune, infection of a single individual will not cause an epidemic. Also, in such immunized populations, susceptible individuals are not likely to become infected. Herd immunity can also refer to the case when unprotected individuals fail to contract a disease because the infecting organism has been banished from the population.T-Lymphocytes, Cytotoxic: Immunized T-lymphocytes which can directly destroy appropriate target cells. These cytotoxic lymphocytes may be generated in vitro in mixed lymphocyte cultures (MLC), in vivo during a graft-versus-host (GVH) reaction, or after immunization with an allograft, tumor cell or virally transformed or chemically modified target cell. The lytic phenomenon is sometimes referred to as cell-mediated lympholysis (CML). These CD8-positive cells are distinct from NATURAL KILLER CELLS and NATURAL KILLER T-CELLS. There are two effector phenotypes: TC1 and TC2.Immunotherapy: Manipulation of the host's immune system in treatment of disease. It includes both active and passive immunization as well as immunosuppressive therapy to prevent graft rejection.Chemokines: Class of pro-inflammatory cytokines that have the ability to attract and activate leukocytes. They can be divided into at least three structural branches: C; (CHEMOKINES, C); CC; (CHEMOKINES, CC); and CXC; (CHEMOKINES, CXC); according to variations in a shared cysteine motif.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.T-Lymphocytes, Helper-Inducer: Subpopulation of CD4+ lymphocytes that cooperate with other lymphocytes (either T or B) to initiate a variety of immune functions. For example, helper-inducer T-cells cooperate with B-cells to produce antibodies to thymus-dependent antigens and with other subpopulations of T-cells to initiate a variety of cell-mediated immune functions.Phagocytosis: The engulfing and degradation of microorganisms; other cells that are dead, dying, or pathogenic; and foreign particles by phagocytic cells (PHAGOCYTES).Lipopolysaccharides: Lipid-containing polysaccharides which are endotoxins and important group-specific antigens. They are often derived from the cell wall of gram-negative bacteria and induce immunoglobulin secretion. The lipopolysaccharide molecule consists of three parts: LIPID A, core polysaccharide, and O-specific chains (O ANTIGENS). When derived from Escherichia coli, lipopolysaccharides serve as polyclonal B-cell mitogens commonly used in laboratory immunology. (From Dorland, 28th ed)Ovalbumin: An albumin obtained from the white of eggs. It is a member of the serpin superfamily.Interleukin-10: A cytokine produced by a variety of cell types, including T-LYMPHOCYTES; MONOCYTES; DENDRITIC CELLS; and EPITHELIAL CELLS that exerts a variety of effects on immunoregulation and INFLAMMATION. Interleukin-10 combines with itself to form a homodimeric molecule that is the biologically active form of the protein.Antibodies, Bacterial: Immunoglobulins produced in a response to BACTERIAL ANTIGENS.CRISPR-Cas Systems: Adaptive antiviral defense mechanisms, in archaea and bacteria, based on DNA repeat arrays called CLUSTERED REGULARLY INTERSPACED SHORT PALINDROMIC REPEATS (CRISPR elements) that function in conjunction with CRISPR-ASSOCIATED PROTEINS (Cas proteins). Several types have been distinguished, including Type I, Type II, and Type III, based on signature motifs of CRISPR-ASSOCIATED PROTEINS.Enzyme-Linked Immunosorbent Assay: An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed.Interleukins: Soluble factors which stimulate growth-related activities of leukocytes as well as other cell types. They enhance cell proliferation and differentiation, DNA synthesis, secretion of other biologically active molecules and responses to immune and inflammatory stimuli.Vaccines, Attenuated: Live vaccines prepared from microorganisms which have undergone physical adaptation (e.g., by radiation or temperature conditioning) or serial passage in laboratory animal hosts or infected tissue/cell cultures, in order to produce avirulent mutant strains capable of inducing protective immunity.Toll-Like Receptor 9: A pattern recognition receptor that binds unmethylated CPG CLUSTERS. It mediates cellular responses to bacterial pathogens by distinguishing between self and bacterial DNA.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.Lymphoid Tissue: Specialized tissues that are components of the lymphatic system. They provide fixed locations within the body where a variety of LYMPHOCYTES can form, mature and multiply. The lymphoid tissues are connected by a network of LYMPHATIC VESSELS.Epitopes, T-Lymphocyte: Antigenic determinants recognized and bound by the T-cell receptor. Epitopes recognized by the T-cell receptor are often located in the inner, unexposed side of the antigen, and become accessible to the T-cell receptors after proteolytic processing of the antigen.Hagfishes: Common name for a family of eel-shaped jawless fishes (Myxinidae), the only family in the order MYXINIFORMES. They are not true vertebrates.Cell Line: Established cell cultures that have the potential to propagate indefinitely.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.Th1-Th2 Balance: Homeostatic control of the immune system by secretion of different cytokines by the Th1 and Th2 cells. The concentration dependent binding of the various cytokines to specific receptors determines the balance (or imbalance leading to disease).Lectins, C-Type: A class of animal lectins that bind to carbohydrate in a calcium-dependent manner. They share a common carbohydrate-binding domain that is structurally distinct from other classes of lectins.beta-Defensins: DEFENSINS found mainly in epithelial cells.Antigens, Bacterial: Substances elaborated by bacteria that have antigenic activity.Mucous Membrane: An EPITHELIUM with MUCUS-secreting cells, such as GOBLET CELLS. It forms the lining of many body cavities, such as the DIGESTIVE TRACT, the RESPIRATORY TRACT, and the reproductive tract. Mucosa, rich in blood and lymph vessels, comprises an inner epithelium, a middle layer (lamina propria) of loose CONNECTIVE TISSUE, and an outer layer (muscularis mucosae) of SMOOTH MUSCLE CELLS that separates the mucosa from submucosa.Cell Communication: Any of several ways in which living cells of an organism communicate with one another, whether by direct contact between cells or by means of chemical signals carried by neurotransmitter substances, hormones, and cyclic AMP.Viruses: Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells.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.Cell Proliferation: All of the processes involved in increasing CELL NUMBER including CELL DIVISION.Vaccines, DNA: Recombinant DNA vectors encoding antigens administered for the prevention or treatment of disease. The host cells take up the DNA, express the antigen, and present it to the immune system in a manner similar to that which would occur during natural infection. This induces humoral and cellular immune responses against the encoded antigens. The vector is called naked DNA because there is no need for complex formulations or delivery agents; the plasmid is injected in saline or other buffers.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.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.Antigens, CD40: A member of the tumor necrosis factor receptor superfamily with specificity for CD40 LIGAND. It is found on mature B-LYMPHOCYTES and some EPITHELIAL CELLS, lymphoid DENDRITIC CELLS. Evidence suggests that CD40-dependent activation of B-cells is important for generation of memory B-cells within the germinal centers. Mutations of the gene for CD40 antigen result in HYPER-IGM IMMUNODEFICIENCY SYNDROME, TYPE 3. Signaling of the receptor occurs through its association with TNF RECEPTOR-ASSOCIATED FACTORS.Orthomyxoviridae Infections: Virus diseases caused by the ORTHOMYXOVIRIDAE.Clustered Regularly Interspaced Short Palindromic Repeats: Repetitive nucleic acid sequences that are principal components of the archaeal and bacterial CRISPR-CAS SYSTEMS, which function as adaptive antiviral defense systems.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.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Viral Vaccines: Suspensions of attenuated or killed viruses administered for the prevention or treatment of infectious viral disease.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Listeria monocytogenes: A species of gram-positive, rod-shaped bacteria widely distributed in nature. It has been isolated from sewage, soil, silage, and from feces of healthy animals and man. Infection with this bacterium leads to encephalitis, meningitis, endocarditis, and abortion.Tumor Necrosis Factor-alpha: Serum glycoprotein produced by activated MACROPHAGES and other mammalian MONONUCLEAR LEUKOCYTES. It has necrotizing activity against tumor cell lines and increases ability to reject tumor transplants. Also known as TNF-alpha, it is only 30% homologous to TNF-beta (LYMPHOTOXIN), but they share TNF RECEPTORS.Cross-Priming: Class I-restricted activation of CD8-POSITIVE LYMPHOCYTES resulting from ANTIGEN PRESENTATION of exogenous ANTIGENS (cross-presentation). This is in contrast to normal activation of these lymphocytes (direct-priming) which results from presentation of endogenous antigens.Toll-Like Receptor 5: A pattern recognition receptor that binds FLAGELLIN. It mediates cellular responses to certain bacterial pathogens.Interleukin-18: A cytokine which resembles IL-1 structurally and IL-12 functionally. It enhances the cytotoxic activity of NK CELLS and CYTOTOXIC T-LYMPHOCYTES, and appears to play a role both as neuroimmunomodulator and in the induction of mucosal immunity.Antibodies, Neutralizing: Antibodies that reduce or abolish some biological activity of a soluble antigen or infectious agent, usually a virus.Inflammation Mediators: The endogenous compounds that mediate inflammation (AUTACOIDS) and related exogenous compounds including the synthetic prostaglandins (PROSTAGLANDINS, SYNTHETIC).Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Infection: Invasion of the host organism by microorganisms that can cause pathological conditions or diseases.Interleukin-4: A soluble factor produced by activated T-LYMPHOCYTES that induces the expression of MHC CLASS II GENES and FC RECEPTORS on B-LYMPHOCYTES and causes their proliferation and differentiation. It also acts on T-lymphocytes, MAST CELLS, and several other hematopoietic lineage cells.Immunologic Factors: Biologically active substances whose activities affect or play a role in the functioning of the immune system.Receptors, Antigen, T-Cell, gamma-delta: T-cell receptors composed of CD3-associated gamma and delta polypeptide chains and expressed primarily in CD4-/CD8- T-cells. The receptors appear to be preferentially located in epithelial sites and probably play a role in the recognition of bacterial antigens. The T-cell receptor gamma/delta chains are separate and not related to the gamma and delta chains which are subunits of CD3 (see ANTIGENS, CD3).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.Gene Expression Profiling: The determination of the pattern of genes expressed at the level of GENETIC TRANSCRIPTION, under specific circumstances or in a specific cell.Reverse Transcriptase Polymerase Chain Reaction: A variation of the PCR technique in which cDNA is made from RNA via reverse transcription. The resultant cDNA is then amplified using standard PCR protocols.Melanoma, Experimental: Experimentally induced tumor that produces MELANIN in animals to provide a model for studying human MELANOMA.Interferon-beta: One of the type I interferons produced by fibroblasts in response to stimulation by live or inactivated virus or by double-stranded RNA. It is a cytokine with antiviral, antiproliferative, and immunomodulating activity.Mice, SCID: Mice homozygous for the mutant autosomal recessive gene "scid" which is located on the centromeric end of chromosome 16. These mice lack mature, functional lymphocytes and are thus highly susceptible to lethal opportunistic infections if not chronically treated with antibiotics. The lack of B- and T-cell immunity resembles severe combined immunodeficiency (SCID) syndrome in human infants. SCID mice are useful as animal models since they are receptive to implantation of a human immune system producing SCID-human (SCID-hu) hematochimeric mice.Petromyzon: A genus of primitive fish in the family Petromyzontidae. The sole species is Petromyzon marinus, known as the sea lamprey. The adult form feeds parasitically on other fish species.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.Antigens, CD1d: A major histocompatibily complex class I-like protein that plays a unique role in the presentation of lipid ANTIGENS to NATURAL KILLER T-CELLS.NF-kappa B: Ubiquitous, inducible, nuclear transcriptional activator that binds to enhancer elements in many different cell types and is activated by pathogenic stimuli. The NF-kappa B complex is a heterodimer composed of two DNA-binding subunits: NF-kappa B1 and relA.Neoplasms: New abnormal growth of tissue. Malignant neoplasms show a greater degree of anaplasia and have the properties of invasion and metastasis, compared to benign neoplasms.Bacterial Proteins: Proteins found in any species of bacterium.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.Interleukin-21 Receptor alpha Subunit: An interleukin-21 receptor subunit that combines with the INTERLEUKIN RECEPTOR COMMON GAMMA SUBUNIT to form a high affinity receptor for interleukin-21. It signals via interaction of its cytoplasmic domain with JANUS KINASES such as JANUS KINASE 1 and JANUS KINASE 3.CRISPR-Associated Proteins: Protein components of the CRISPR-CAS SYSTEMS for anti-viral defense in ARCHAEA and BACTERIA. These are proteins that carry out a variety of functions during the creation and expansion of the CRISPR ARRAYS, the capture of new CRISPR SPACERS, biogenesis of SMALL INTERFERING RNA (CRISPR or crRNAs), and the targeting and silencing of invading viruses and plasmids. They include DNA HELICASES; RNA-BINDING PROTEINS; ENDONUCLEASES; and RNA and DNA POLYMERASES.Neutrophils: Granular leukocytes having a nucleus with three to five lobes connected by slender threads of chromatin, and cytoplasm containing fine inconspicuous granules and stainable by neutral dyes.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.Immunophenotyping: Process of classifying cells of the immune system based on structural and functional differences. The process is commonly used to analyze and sort T-lymphocytes into subsets based on CD antigens by the technique of flow cytometry.Toll-Like Receptor 3: A pattern recognition receptor that binds DOUBLE-STRANDED RNA. It mediates cellular responses to certain viral pathogens.Toll-Like Receptor 8: A pattern recognition receptor that recognizes GUANOSINE and URIDINE-rich single-stranded RNA.Interleukin-12 Subunit p40: A cytokine subunit that is a component of both interleukin-12 and interleukin-23. It binds to the INTERLEUKIN-12 SUBUNIT P35 via a disulfide bond to form interleukin-12 and to INTERLEUKIN-23 SUBUNIT P19 to form interleukin-23.Toll-Like Receptor 7: A pattern recognition receptor that binds several forms of imidazo-quinoline including the antiviral compound Imiquimod.Antigens, CD86: A costimulatory ligand expressed by ANTIGEN-PRESENTING CELLS that binds to CD28 ANTIGEN with high specificity and to CTLA-4 ANTIGEN with low specificity. The interaction of CD86 with CD28 ANTIGEN provides a stimulatory signal to T-LYMPHOCYTES, while its interaction with CTLA-4 ANTIGEN may play a role in inducing PERIPHERAL TOLERANCE.Vertebrates: Animals having a vertebral column, members of the phylum Chordata, subphylum Craniata comprising mammals, birds, reptiles, amphibians, and fishes.Autophagy: The segregation and degradation of damaged or unwanted cytoplasmic constituents by autophagic vacuoles (cytolysosomes) composed of LYSOSOMES containing cellular components in the process of digestion; it plays an important role in BIOLOGICAL METAMORPHOSIS of amphibians, in the removal of bone by osteoclasts, and in the degradation of normal cell components in nutritional deficiency states.Disease Susceptibility: A constitution or condition of the body which makes the tissues react in special ways to certain extrinsic stimuli and thus tends to make the individual more than usually susceptible to certain diseases.CD40 Ligand: A membrane glycoprotein and differentiation antigen expressed on the surface of T-cells that binds to CD40 ANTIGENS on B-LYMPHOCYTES and induces their proliferation. Mutation of the gene for CD40 ligand is a cause of HYPER-IGM IMMUNODEFICIENCY SYNDROME, TYPE 1.Phagocytes: Cells that can carry out the process of PHAGOCYTOSIS.Mycobacterium tuberculosis: A species of gram-positive, aerobic bacteria that produces TUBERCULOSIS in humans, other primates, CATTLE; DOGS; and some other animals which have contact with humans. Growth tends to be in serpentine, cordlike masses in which the bacilli show a parallel orientation.Selection, Genetic: Differential and non-random reproduction of different genotypes, operating to alter the gene frequencies within a population.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)Myeloid Cells: The classes of BONE MARROW-derived blood cells in the monocytic series (MONOCYTES and their precursors) and granulocytic series (GRANULOCYTES and their precursors).Nod2 Signaling Adaptor Protein: A NOD signaling adaptor protein that contains two C-terminal leucine-rich domains which recognize bacterial PEPTIDOGLYCAN. It signals via an N-terminal capase recruitment domain that interacts with other CARD SIGNALING ADAPTOR PROTEINS such as RIP SERINE-THEONINE KINASES. The protein plays a role in the host defense response by signaling the activation of CASPASES and the MAP KINASE SIGNALING SYSTEM. Mutations of the gene encoding the nucleotide oligomerization domain 2 protein have been associated with increased susceptibility to CROHN DISEASE.Intestinal Mucosa: Lining of the INTESTINES, consisting of an inner EPITHELIUM, a middle LAMINA PROPRIA, and an outer MUSCULARIS MUCOSAE. In the SMALL INTESTINE, the mucosa is characterized by a series of folds and abundance of absorptive cells (ENTEROCYTES) with MICROVILLI.Species Specificity: The restriction of a characteristic behavior, anatomical structure or physical system, such as immune response; metabolic response, or gene or gene variant to the members of one species. It refers to that property which differentiates one species from another but it is also used for phylogenetic levels higher or lower than the species.Poly I-C: Interferon inducer consisting of a synthetic, mismatched double-stranded RNA. The polymer is made of one strand each of polyinosinic acid and polycytidylic acid.Immunoglobulin A: Represents 15-20% of the human serum immunoglobulins, mostly as the 4-chain polymer in humans or dimer in other mammals. Secretory IgA (IMMUNOGLOBULIN A, SECRETORY) is the main immunoglobulin in secretions.Leukocytes, Mononuclear: Mature LYMPHOCYTES and MONOCYTES transported by the blood to the body's extravascular space. They are morphologically distinguishable from mature granulocytic leukocytes by their large, non-lobed nuclei and lack of coarse, heavily stained cytoplasmic granules.Immunotherapy, Adoptive: Form of adoptive transfer where cells with antitumor activity are transferred to the tumor-bearing host in order to mediate tumor regression. The lymphoid cells commonly used are lymphokine-activated killer (LAK) cells and tumor-infiltrating lymphocytes (TIL). This is usually considered a form of passive immunotherapy. (From DeVita, et al., Cancer, 1993, pp.305-7, 314)Interleukin-2: A soluble substance elaborated by antigen- or mitogen-stimulated T-LYMPHOCYTES which induces DNA synthesis in naive lymphocytes.Hypersensitivity, Delayed: An increased reactivity to specific antigens mediated not by antibodies but by cells.Lymphocyte Subsets: A classification of lymphocytes based on structurally or functionally different populations of cells.Interferon-alpha: One of the type I interferons produced by peripheral blood leukocytes or lymphoblastoid cells. In addition to antiviral activity, it activates NATURAL KILLER CELLS and B-LYMPHOCYTES, and down-regulates VASCULAR ENDOTHELIAL GROWTH FACTOR expression through PI-3 KINASE and MAPK KINASES signaling pathways.Neuroimmunomodulation: The biochemical and electrophysiological interactions between the NERVOUS SYSTEM and IMMUNE SYSTEM.Defensins: Family of antimicrobial peptides that have been identified in humans, animals, and plants. They are thought to play a role in host defenses against infections, inflammation, wound repair, and acquired immunity.Inflammasomes: Multiprotein complexes that mediate the activation of CASPASE-1. Dysregulation of inflammasomes has also been linked to a number of autoinflammatory and autoimmune disorders.Autoimmune Diseases: Disorders that are characterized by the production of antibodies that react with host tissues or immune effector cells that are autoreactive to endogenous peptides.Receptors, Chemokine: Cell surface glycoproteins that bind to chemokines and thus mediate the migration of pro-inflammatory molecules. The receptors are members of the seven-transmembrane G protein-coupled receptor family. Like the CHEMOKINES themselves, the receptors can be divided into at least three structural branches: CR, CCR, and CXCR, according to variations in a shared cysteine motif.Coculture Techniques: A technique of culturing mixed cell types in vitro to allow their synergistic or antagonistic interactions, such as on CELL DIFFERENTIATION or APOPTOSIS. Coculture can be of different types of cells, tissues, or organs from normal or disease states.Gene Expression: The phenotypic manifestation of a gene or genes by the processes of GENETIC TRANSCRIPTION and GENETIC TRANSLATION.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.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.Host-Parasite Interactions: The relationship between an invertebrate and another organism (the host), one of which lives at the expense of the other. Traditionally excluded from definition of parasites are pathogenic BACTERIA; FUNGI; VIRUSES; and PLANTS; though they may live parasitically.Antigens, CD80: A costimulatory ligand expressed by ANTIGEN-PRESENTING CELLS that binds to CTLA-4 ANTIGEN with high specificity and to CD28 ANTIGEN with low specificity. The interaction of CD80 with CD28 ANTIGEN provides a costimulatory signal to T-LYMPHOCYTES, while its interaction with CTLA-4 ANTIGEN may play a role in inducing PERIPHERAL TOLERANCE.Self Tolerance: The normal lack of the ability to produce an immunological response to autologous (self) antigens. A breakdown of self tolerance leads to autoimmune diseases. The ability to recognize the difference between self and non-self is the prime function of the immune system.Interleukin Receptor Common gamma Subunit: An interleukin receptor subunit that was originally discovered as a component of the INTERLEUKIN 2 RECEPTOR. It was subsequently found to be a component of several other receptors including the INTERLEUKIN 4 RECEPTOR, the INTERLEUKIN 7 RECEPTOR, the INTERLEUKIN-9 RECEPTOR, the INTERLEUKIN-15 RECEPTOR, and the INTERLEUKIN-21 RECEPTOR. Mutations in the gene for the interleukin receptor common gamma chain have been associated with X-LINKED COMBINED IMMUNODEFICIENCY DISEASES.Immunoglobulin M: A class of immunoglobulin bearing mu chains (IMMUNOGLOBULIN MU-CHAINS). IgM can fix COMPLEMENT. The name comes from its high molecular weight and originally being called a macroglobulin.Lymph Nodes: They are oval or bean shaped bodies (1 - 30 mm in diameter) located along the lymphatic system.Virulence: The degree of pathogenicity within a group or species of microorganisms or viruses as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenic capacity of an organism is determined by its VIRULENCE FACTORS.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.Mice, Mutant Strains: Mice bearing mutant genes which are phenotypically expressed in the animals.Interleukin-23: A heterodimeric cytokine that plays a role in innate and adaptive immune responses. Interleukin-23 is comprised of a unique 19 kDa subunit and 40 kDa subunit that is shared with INTERLEUKIN-12. It is produced by DENDRITIC CELLS; MACROPHAGES and a variety of other immune cellsVaccines, Synthetic: Small synthetic peptides that mimic surface antigens of pathogens and are immunogenic, or vaccines manufactured with the aid of recombinant DNA techniques. The latter vaccines may also be whole viruses whose nucleic acids have been modified.Genetic Vectors: DNA molecules capable of autonomous replication within a host cell and into which other DNA sequences can be inserted and thus amplified. Many are derived from PLASMIDS; BACTERIOPHAGES; or VIRUSES. They are used for transporting foreign genes into recipient cells. Genetic vectors possess a functional replicator site and contain GENETIC MARKERS to facilitate their selective recognition.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.Lymphocyte Count: The number of LYMPHOCYTES per unit volume of BLOOD.Physiology, Comparative: The biological science concerned with similarities or differences in the life-supporting functions and processes of different species.alpha-Defensins: DEFENSINS found in azurophilic granules of neutrophils and in the secretory granules of intestinal PANETH CELLS.Receptors, Interleukin-17: Cell surface receptors for INTERLEUKIN-17. Several subtypes of receptors have been found, each with its own in specificity for interleukin-17 subtype.