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.Memory: Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory.Memory Disorders: Disturbances in registering an impression, in the retention of an acquired impression, or in the recall of an impression. Memory impairments are associated with DEMENTIA; CRANIOCEREBRAL TRAUMA; ENCEPHALITIS; ALCOHOLISM (see also ALCOHOL AMNESTIC DISORDER); SCHIZOPHRENIA; and other conditions.Memory, Short-Term: Remembrance of information for a few seconds to hours.Immunization, Secondary: Any immunization following a primary immunization and involving exposure to the same or a closely related antigen.Antibody Formation: The production of ANTIBODIES by proliferating and differentiated B-LYMPHOCYTES under stimulation by ANTIGENS.Memory, Long-Term: Remembrance of information from 3 or more years previously.Vaccines, Conjugate: Semisynthetic vaccines consisting of polysaccharide antigens from microorganisms attached to protein carrier molecules. The carrier protein is recognized by macrophages and T-cells thus enhancing immunity. Conjugate vaccines induce antibody formation in people not responsive to polysaccharide alone, induce higher levels of antibody, and show a booster response on repeated injection.Memory, Episodic: Type of declarative memory, consisting of personal memory in contrast to general knowledge.Meningococcal Vaccines: Vaccines or candidate vaccines used to prevent infection with NEISSERIA MENINGITIDIS.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.Antibodies, Bacterial: Immunoglobulins produced in a response to BACTERIAL ANTIGENS.Immunization: Deliberate stimulation of the host's immune response. ACTIVE IMMUNIZATION involves administration of ANTIGENS or IMMUNOLOGIC ADJUVANTS. PASSIVE IMMUNIZATION involves administration of IMMUNE SERA or LYMPHOCYTES or their extracts (e.g., transfer factor, immune RNA) or transplantation of immunocompetent cell producing tissue (thymus or bone marrow).Thoracic Duct: The largest lymphatic vessel that passes through the chest and drains into the SUBCLAVIAN VEIN.Immunoglobulin G: The major immunoglobulin isotype class in normal human serum. There are several isotype subclasses of IgG, for example, IgG1, IgG2A, and IgG2B.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.Tetanus ToxoidAntibody-Producing Cells: Cells of the lymphoid series that can react with antigen to produce specific cell products called antibodies. Various cell subpopulations, often B-lymphocytes, can be defined, based on the different classes of immunoglobulins that they synthesize.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.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.Mice, Inbred C57BLLymphocyte 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.Hemolytic Plaque Technique: A method to identify and enumerate cells that are synthesizing ANTIBODIES against ANTIGENS or HAPTENS conjugated to sheep RED BLOOD CELLS. The sheep red blood cells surrounding cells secreting antibody are lysed by added COMPLEMENT producing a clear zone of HEMOLYSIS. (From Illustrated Dictionary of Immunology, 3rd ed)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.Antigens: Substances that are recognized by the immune system and induce an immune reaction.gamma-Globulins: Serum globulins that migrate to the gamma region (most positively charged) upon ELECTROPHORESIS. At one time, gamma-globulins came to be used as a synonym for immunoglobulins since most immunoglobulins are gamma globulins and conversely most gamma globulins are immunoglobulins. But since some immunoglobulins exhibit an alpha or beta electrophoretic mobility, that usage is in decline.Mental Recall: The process whereby a representation of past experience is elicited.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.Antibody Affinity: A measure of the binding strength between antibody and a simple hapten or antigen determinant. It depends on the closeness of stereochemical fit between antibody combining sites and antigen determinants, on the size of the area of contact between them, and on the distribution of charged and hydrophobic groups. It includes the concept of "avidity," which refers to the strength of the antigen-antibody bond after formation of reversible complexes.Vaccination: Administration of vaccines to stimulate the host's immune response. This includes any preparation intended for active immunological prophylaxis.Spleen: An encapsulated lymphatic organ through which venous blood filters.Haemophilus influenzae type b: A type of H. influenzae isolated most frequently from biotype I. Prior to vaccine availability, it was a leading cause of childhood meningitis.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Antigens, CD27: A member of the tumor necrosis factor receptor superfamily found on most T-LYMPHOCYTES. Activation of the receptor by CD70 ANTIGEN results in the increased proliferation of CD4-POSITIVE T-LYMPHOCYTES and CD8-POSITIVE T-LYMPHOCYTES. Signaling by the activated receptor occurs through its association with TNF RECEPTOR-ASSOCIATED FACTORS.Immunization Schedule: Schedule giving optimum times usually for primary and/or secondary immunization.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.Mice, Inbred BALB CNeisseria meningitidis: A species of gram-negative, aerobic BACTERIA. It is a commensal and pathogen only of humans, and can be carried asymptomatically in the NASOPHARYNX. When found in cerebrospinal fluid it is the causative agent of cerebrospinal meningitis (MENINGITIS, MENINGOCOCCAL). It is also found in venereal discharges and blood. There are at least 13 serogroups based on antigenic differences in the capsular polysaccharides; the ones causing most meningitis infections being A, B, C, Y, and W-135. Each serogroup can be further classified by serotype, serosubtype, and immunotype.Polysaccharides, Bacterial: Polysaccharides found in bacteria and in capsules thereof.Haemophilus Vaccines: Vaccines or candidate vaccines containing antigenic polysaccharides from Haemophilus influenzae and designed to prevent infection. The vaccine can contain the polysaccharides alone or more frequently polysaccharides conjugated to carrier molecules. It is also seen as a combined vaccine with diphtheria-tetanus-pertussis vaccine.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.HemocyaninMaze Learning: Learning the correct route through a maze to obtain reinforcement. It is used for human or animal populations. (Thesaurus of Psychological Index Terms, 6th ed)Neuropsychological Tests: Tests designed to assess neurological function associated with certain behaviors. They are used in diagnosing brain dysfunction or damage and central nervous system disorders or injury.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.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.Retention (Psychology): The persistence to perform a learned behavior (facts or experiences) after an interval has elapsed in which there has been no performance or practice of the behavior.Recognition (Psychology): The knowledge or perception that someone or something present has been previously encountered.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.Immunization, Passive: Transfer of immunity from immunized to non-immune host by administration of serum antibodies, or transplantation of lymphocytes (ADOPTIVE TRANSFER).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.Germinal Center: The activated center of a lymphoid follicle in secondary lymphoid tissue where B-LYMPHOCYTES are stimulated by antigens and helper T cells (T-LYMPHOCYTES, HELPER-INDUCER) are stimulated to generate memory cells.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).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.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).Hippocampus: A curved elevation of GRAY MATTER extending the entire length of the floor of the TEMPORAL HORN of the LATERAL VENTRICLE (see also TEMPORAL LOBE). The hippocampus proper, subiculum, and DENTATE GYRUS constitute the hippocampal formation. Sometimes authors include the ENTORHINAL CORTEX in the hippocampal formation.Haptens: Small antigenic determinants capable of eliciting an immune response only when coupled to a carrier. Haptens bind to antibodies but by themselves cannot elicit an antibody response.Antibodies, Viral: Immunoglobulins produced in response to VIRAL ANTIGENS.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.Learning: Relatively permanent change in behavior that is the result of past experience or practice. The concept includes the acquisition of knowledge.Pneumococcal Vaccines: Vaccines or candidate vaccines used to prevent infections with STREPTOCOCCUS PNEUMONIAE.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.B-Lymphocyte Subsets: A classification of B-lymphocytes based on structurally or functionally different populations of cells.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.Antigens, Bacterial: Substances elaborated by bacteria that have antigenic activity.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.Meningococcal Infections: Infections with bacteria of the species NEISSERIA MENINGITIDIS.Lymphocyte Count: The number of LYMPHOCYTES per unit volume of BLOOD.Association Learning: The principle that items experienced together enter into a connection, so that one tends to reinstate the other.Mice, Transgenic: Laboratory mice that have been produced from a genetically manipulated EGG or EMBRYO, MAMMALIAN.Bacterial Vaccines: Suspensions of attenuated or killed bacteria administered for the prevention or treatment of infectious bacterial disease.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).Erythrocytes: Red blood cells. Mature erythrocytes are non-nucleated, biconcave disks containing HEMOGLOBIN whose function is to transport OXYGEN.Hypersensitivity, Delayed: An increased reactivity to specific antigens mediated not by antibodies but by cells.Mice, Inbred Strains: Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations, or by parent x offspring matings carried out with certain restrictions. All animals within an inbred strain trace back to a common ancestor in the twentieth generation.Sheep: Any of the ruminant mammals with curved horns in the genus Ovis, family Bovidae. They possess lachrymal grooves and interdigital glands, which are absent in GOATS.Amnesia: Pathologic partial or complete loss of the ability to recall past experiences (AMNESIA, RETROGRADE) or to form new memories (AMNESIA, ANTEROGRADE). This condition may be of organic or psychologic origin. Organic forms of amnesia are usually associated with dysfunction of the DIENCEPHALON or HIPPOCAMPUS. (From Adams et al., Principles of Neurology, 6th ed, pp426-7)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.Verbal Learning: Learning to respond verbally to a verbal stimulus cue.Mice, Inbred CBAMice, 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.Fear: The affective response to an actual current external danger which subsides with the elimination of the threatening condition.Lymph Nodes: They are oval or bean shaped bodies (1 - 30 mm in diameter) located along the lymphatic system.Thymus Gland: A single, unpaired primary lymphoid organ situated in the MEDIASTINUM, extending superiorly into the neck to the lower edge of the THYROID GLAND and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat.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.Dose-Response Relationship, Immunologic: A specific immune response elicited by a specific dose of an immunologically active substance or cell in an organism, tissue, or cell.Spatial Behavior: Reactions of an individual or groups of individuals with relation to the immediate surrounding area including the animate or inanimate objects within that area.Plasma Cells: Specialized forms of antibody-producing B-LYMPHOCYTES. They synthesize and secrete immunoglobulin. They are found only in lymphoid organs and at sites of immune responses and normally do not circulate in the blood or lymph. (Rosen et al., Dictionary of Immunology, 1989, p169 & Abbas et al., Cellular and Molecular Immunology, 2d ed, p20)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.Cognition: Intellectual or mental process whereby an organism obtains knowledge.Administration, Oral: The giving of drugs, chemicals, or other substances by mouth.Avoidance Learning: A response to a cue that is instrumental in avoiding a noxious experience.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).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.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.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.Conditioning (Psychology): A general term referring to the learning of some particular response.Reaction Time: The time from the onset of a stimulus until a response is observed.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.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.Antigens, Viral: Substances elaborated by viruses that have antigenic activity.Epitopes: Sites on an antigen that interact with specific antibodies.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.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.Conditioning, Classical: Learning that takes place when a conditioned stimulus is paired with an unconditioned stimulus.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.Analysis of Variance: A statistical technique that isolates and assesses the contributions of categorical independent variables to variation in the mean of a continuous dependent variable.Cell Differentiation: Progressive restriction of the developmental potential and increasing specialization of function that leads to the formation of specialized cells, tissues, and organs.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.Cognition Disorders: Disturbances in mental processes related to learning, thinking, reasoning, and judgment.Psychomotor Performance: The coordination of a sensory or ideational (cognitive) process and a motor activity.Behavior, Animal: The observable response an animal makes to any situation.Brain: The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.Attention: Focusing on certain aspects of current experience to the exclusion of others. It is the act of heeding or taking notice or concentrating.Prefrontal Cortex: The rostral part of the frontal lobe, bounded by the inferior precentral fissure in humans, which receives projection fibers from the MEDIODORSAL NUCLEUS OF THE THALAMUS. The prefrontal cortex receives afferent fibers from numerous structures of the DIENCEPHALON; MESENCEPHALON; and LIMBIC SYSTEM as well as cortical afferents of visual, auditory, and somatic origin.Brain Mapping: Imaging techniques used to colocalize sites of brain functions or physiological activity with brain structures.Cues: Signals for an action; that specific portion of a perceptual field or pattern of stimuli to which a subject has learned to respond.Amygdala: Almond-shaped group of basal nuclei anterior to the INFERIOR HORN OF THE LATERAL VENTRICLE of the TEMPORAL LOBE. The amygdala is part of the limbic system.Bone Marrow: The soft tissue filling the cavities of bones. Bone marrow exists in two types, yellow and red. Yellow marrow is found in the large cavities of large bones and consists mostly of fat cells and a few primitive blood cells. Red marrow is a hematopoietic tissue and is the site of production of erythrocytes and granular leukocytes. Bone marrow is made up of a framework of connective tissue containing branching fibers with the frame being filled with marrow cells.Temporal Lobe: Lower lateral part of the cerebral hemisphere responsible for auditory, olfactory, and semantic processing. It is located inferior to the lateral fissure and anterior to the OCCIPITAL LOBE.Repression, Psychology: The active mental process of keeping out and ejecting, banishing from consciousness, ideas or impulses that are unacceptable to it.Cell Division: The fission of a CELL. It includes CYTOKINESIS, when the CYTOPLASM of a cell is divided, and CELL NUCLEUS DIVISION.Photic Stimulation: Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity.Amnesia, Retrograde: Loss of the ability to recall information that had been previously encoded in memory prior to a specified or approximate point in time. This process may be organic or psychogenic in origin. Organic forms may be associated with CRANIOCEREBRAL TRAUMA; CEREBROVASCULAR ACCIDENTS; SEIZURES; DEMENTIA; and a wide variety of other conditions that impair cerebral function. (From Adams et al., Principles of Neurology, 6th ed, pp426-9)Neuronal Plasticity: The capacity of the NERVOUS SYSTEM to change its reactivity as the result of successive activations.Long-Term Potentiation: A persistent increase in synaptic efficacy, usually induced by appropriate activation of the same synapses. The phenomenological properties of long-term potentiation suggest that it may be a cellular mechanism of learning and memory.Aging: The gradual irreversible changes in structure and function of an organism that occur as a result of the passage of time.Pattern Recognition, Visual: Mental process to visually perceive a critical number of facts (the pattern), such as characters, shapes, displays, or designs.Paired-Associate Learning: Learning in which the subject must respond with one word or syllable when presented with another word or syllable.Exploratory Behavior: The tendency to explore or investigate a novel environment. It is considered a motivation not clearly distinguishable from curiosity.Mushroom Bodies: Prominent lobed neuropils found in ANNELIDA and all ARTHROPODS except crustaceans. They are thought to be involved in olfactory learning and memory.Autobiography as Topic: The life of a person written by himself or herself. (Harrod's Librarians' Glossary, 7th ed)Visual Perception: The selecting and organizing of visual stimuli based on the individual's past experience.Executive Function: A set of cognitive functions that controls complex, goal-directed thought and behavior. Executive function involves multiple domains, such as CONCEPT FORMATION, goal management, cognitive flexibility, INHIBITION control, and WORKING MEMORY. Impaired executive function is seen in a range of disorders, e.g., SCHIZOPHRENIA; and ADHD.Rats, Long-Evans: An outbred strain of rats developed in 1915 by crossing several Wistar Institute white females with a wild gray male. Inbred strains have been derived from this original outbred strain, including Long-Evans cinnamon rats (RATS, INBRED LEC) and Otsuka-Long-Evans-Tokushima Fatty rats (RATS, INBRED OLETF), which are models for Wilson's disease and non-insulin dependent diabetes mellitus, respectively.Learning Disorders: Conditions characterized by a significant discrepancy between an individual's perceived level of intellect and their ability to acquire new language and other cognitive skills. These disorders may result from organic or psychological conditions. Relatively common subtypes include DYSLEXIA, DYSCALCULIA, and DYSGRAPHIA.Emotions: Those affective states which can be experienced and have arousing and motivational properties.Neurons: The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.Amnesia, Anterograde: Loss of the ability to form new memories beyond a certain point in time. This condition may be organic or psychogenic in origin. Organically induced anterograde amnesia may follow CRANIOCEREBRAL TRAUMA; SEIZURES; ANOXIA; and other conditions which adversely affect neural structures associated with memory formation (e.g., the HIPPOCAMPUS; FORNIX (BRAIN); MAMMILLARY BODIES; and ANTERIOR THALAMIC NUCLEI). (From Memory 1997 Jan-Mar;5(1-2):49-71)Scopolamine Hydrobromide: An alkaloid from SOLANACEAE, especially DATURA and SCOPOLIA. Scopolamine and its quaternary derivatives act as antimuscarinics like ATROPINE, but may have more central nervous system effects. Among the many uses are as an anesthetic premedication, in URINARY INCONTINENCE, in MOTION SICKNESS, as an antispasmodic, and as a mydriatic and cycloplegic.Alzheimer Disease: A degenerative disease of the BRAIN characterized by the insidious onset of DEMENTIA. Impairment of MEMORY, judgment, attention span, and problem solving skills are followed by severe APRAXIAS and a global loss of cognitive abilities. The condition primarily occurs after age 60, and is marked pathologically by severe cortical atrophy and the triad of SENILE PLAQUES; NEUROFIBRILLARY TANGLES; and NEUROPIL THREADS. (From Adams et al., Principles of Neurology, 6th ed, pp1049-57)Extinction, Psychological: The procedure of presenting the conditioned stimulus without REINFORCEMENT to an organism previously conditioned. It refers also to the diminution of a conditioned response resulting from this procedure.Electroshock: Induction of a stress reaction in experimental subjects by means of an electrical shock; applies to either convulsive or non-convulsive states.Neural Pathways: Neural tracts connecting one part of the nervous system with another.Functional Laterality: Behavioral manifestations of cerebral dominance in which there is preferential use and superior functioning of either the left or the right side, as in the preferred use of the right hand or right foot.Nerve Net: A meshlike structure composed of interconnecting nerve cells that are separated at the synaptic junction or joined to one another by cytoplasmic processes. In invertebrates, for example, the nerve net allows nerve impulses to spread over a wide area of the net because synapses can pass information in any direction.Association: A functional relationship between psychological phenomena of such nature that the presence of one tends to evoke the other; also, the process by which such a relationship is established.Smell: The ability to detect scents or odors, such as the function of OLFACTORY RECEPTOR NEURONS.
Explicit memory: Explicit memory is the conscious, intentional recollection of previous experiences and information. People use explicit memory throughout the day, such as remembering the time of an appointment or recollecting an event from years ago.Memory clinic: A memory clinic is a dedicated medical clinic specialising in the assessment and diagnosis of memory disorders. Memory clinics were first seen in the UK in the 1980s, mainly in academic research centres.Conjugate vaccine: A conjugate vaccine is created by covalently attaching a poor (polysaccharide) antigen to a carrier protein (preferably from the same microorganism), thereby conferring the immunological attributes of the carrier to the attached antigen.Time-Based Prospective Memory: Time-based prospective memory is a type of prospective memory in which remembrance is triggered by a time-related cue that indicates that a given action needs to be performed. An example is remembering to watch a television program at 3 p.Meningococcal vaccinePolyclonal B cell response: Polyclonal B cell response is a natural mode of immune response exhibited by the adaptive immune system of mammals. It ensures that a single antigen is recognized and attacked through its overlapping parts, called epitopes, by multiple clones of B cell.ImmunizationLumbar lymph trunk: The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymph glands.CD4 immunoadhesin: CD4 immunoadhesin is a recombinant fusion protein consisting of a combination of CD4 and the fragment crystallizable region.Cell-mediated immunity: Cell mediated immunity is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. Historically, the immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum) and cellular immunity, for which the protective function of immunization was associated with cells.List of GlaxoSmithKline products: This is a list of products manufactured by the multinational pharmaceutical, biologics, vaccines and consumer healthcare company GlaxoSmithKline.PMHC cellular microarray: PMHC cellular microarrays are a type of cellular microarray that has been spotted with pMHC complexes peptide-MHC class I or peptide-MHC class II.History and naming of human leukocyte antigens: Human leukocyte antigens (HLA) began as a list of antigens identified as a result of transplant rejection. The antigens were initially identified by categorizing and performing massive statistical analyses on interactions between blood types.Spaced retrieval: Spaced retrieval, also known as expanded retrieval or uniform retrieval, is a learning technique, which requires users to rehearse information to be learned at different and increasing spaced intervals of time or a set uniform amount of time.Haslam, C.Passive immunity: Passive immunity is the transfer of active humoral immunity in the form of ready-made antibodies, from one individual to another. Passive immunity can occur naturally, when maternal antibodies are transferred to the fetus through the placenta, and can also be induced artificially, when high levels of human (or horse) antibodies specific for a pathogen or toxin are transferred to non-immune through blood products that contain antibodies like immune globulin.Avidity: In the context of biochemistry, avidity refers to the accumulated strength of multiple affinities of individual non-covalent binding interactions, such as between a protein receptor and its ligand, and is commonly referred to as functional affinity. As such, avidity is distinct from affinity, which describes the strength of a single interaction.VaccinationPeriarteriolar lymphoid sheaths: Periarteriolar lymphoid sheaths (or periarterial lymphatic sheaths, or PALS) are a portion of the white pulp of the spleen. They are populated largely by T cells and surround central arteries within the spleen; the PALS T-cells are presented with blood borne antigens via myeloid dendritic cells.Temporal analysis of products: Temporal Analysis of Products (TAP), (TAP-2), (TAP-3) is an experimental technique for studyingDPT vaccineNeisseria meningitidis: Neisseria meningitidis, often referred to as meningococcus, is a gram negative bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life-threatening sepsis. The bacterium is referred to as a coccus because it is round, and more specifically, diplococcus because of its tendency to form pairs.Polysaccharide encapsulated bacteriaMegathura crenulata: Megathura crenulata, common name the great keyhole limpet or giant keyhole limpet, is a northeast Pacific species of limpet in the family Fissurellidae. Rosenberg, G.Learning Plan: A Learning Plan is a document (possibly an interactive or on-line document) that is used to plan learning, usually over an extended period of time.Repeatable Battery for the Assessment of Neuropsychological Status: The Repeatable Battery for the Assessment of Neuropsychological Status is a neuropsychological assessment initially introduced in 1998. It consists of ten subtests which give five scores, one for each of the five domains tested (immediate memory, visuospatial/constructional, language, attention, delayed memory).Immunologic adjuvant: In immunology, an adjuvant is a component that potentiates the immune responses to an antigen and/or modulates it towards the desired immune responses. The word “adjuvant” comes from the Latin word adiuvare, meaning to help or aid.Hyperimmune globulin: Hyperimmune globulin is similar to intravenous immunoglobulin (IVIG) except that it is prepared from the plasma of donors with high titers of antibody against a specific organism or antigen. Some agents against which hyperimmune globulins are available include hepatitis B, rabies, tetanus toxin, varicella-zoster, etc.SeroconversionGerminal center B-cell like diffuse large B-cell lymphoma: Gene expression profiling has revealed that diffuse large B-cell lymphoma (DLBCL) is composed of at least 3 different sub-groups, each having distinct oncogenic mechanisms that respond to therapies in different ways. Germinal Center B-Cell like (GCB) DLBCLs appear to arise from normal germinal center B cells, while Activated B-cell like (ABC) DLBCLs are thought to arise from postgerminal center B cells that are arrested during plasmacytic differentiation.Place cellHapten: Haptens are small molecules that elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself. (In general, only large molecules, infectious agents, or insoluble foreign matter can elicit an immune response in the body.Pneumococcal vaccine: A pneumococcal vaccine is a vaccine against Streptococcus pneumoniae.Intraepithelial lymphocyte: Intraepithelial lymphocytes (IEL) are lymphocytes found in the epithelial layer of mammalian mucosal linings, such as the gastrointestinal (GI) tract and reproductive tract. However, unlike other T cells, IELs do not need priming.Immunophenotyping: Immunophenotyping is a technique used to study the protein expressed by cells. This technique is commonly used in basic science research and laboratory diagnostic purpose.Eva Engvall: Eva Engvall, born 1940, is one of the scientists who invented ELISA in 1971.Eva Engvall, The Scientist 1995, 9(18):8Statistical relational learning: Statistical relational learning (SRL) is a subdiscipline of artificial intelligence and machine learning that is concerned with domain models that exhibit both uncertainty (which can be dealt with using statistical methods) and complex, relational structure. Typically, the knowledge representation formalisms developed in SRL use (a subset of) first-order logic to describe relational properties of a domain in a general manner (universal quantification) and draw upon probabilistic graphical models (such as Bayesian networks or Markov networks) to model the uncertainty; some also build upon the methods of inductive logic programming.Immunization during pregnancy: Immunization during pregnancy, that is the administration of a vaccine to a pregnant woman, is not a routine event as it is generally preferred to administer vaccines either prior to conception or in the postpartum period. When widespread vaccination is used, the risk for an unvaccinated pregnant patient to be exposed to a related infection is low, allowing for postponement, in general, of routine vaccinations to the postpartum period.Primary and secondary antibodies: Primary and secondary antibodies are two groups of antibodies that are classified based on whether they bind to antigens or proteins directly or target another (primary) antibody that, in turn, is bound to an antigen or protein.Erythrocrine: Erythrocrine describes red blood cell or erythrocyte for production and release of signaling molecules. The term “erythrocrine“ was coined by Song et al.Corriedale: Corriedale sheep are a dual purpose breed, meaning they are used both in the production of wool and meat. The Corriedale is the oldest of all the crossbred breeds, a Merino-Lincoln cross developed almost simultaneously in Australia and New ZealandStock Types, The Land, North Richmond, c.Amnesia (Chumbawamba song): "Amnesia" is the second single from Chumbawamba's album Tubthumper, released on January 28, 1998. The song's lyrical content addresses the sense of betrayal that English leftists felt during the rise of New Labour.CTL-mediated cytotoxicityFear conditioning: Fear conditioning is a behavioral paradigm in which organisms learn to predict aversive events. It is a form of learning in which an aversive stimulus (e.Inferior mesenteric lymph nodes: The inferior mesenteric lymph nodes consist of:Hassall's corpuscles: Hassall's corpuscles (or thymic corpuscles (bodies)) are structures found in the medulla of the human thymus, formed from eosinophilic type VI epithelial reticular cells arranged concentrically. These concentric corpuscles are composed of a central mass, consisting of one or more granular cells, and of a capsule formed of epithelioid cells.ImmunotherapyPlasma cellFlow cytometry: In biotechnology, flow cytometry is a laser-based, biophysical technology employed in cell counting, cell sorting, biomarker detection and protein engineering, by suspending cells in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and chemical characteristics of up to thousands of particles per second.Cognitive skill: Cognitive functioning is a term referring to a human’s ability to process to (thoughts) that should not deplete on a large scale in healthy individuals. Cognition mainly refers to things like memory, the ability to learn new information, speech, understanding of written material.Osmotic controlled-release oral delivery system: OROS (Osmotic [Controlled] Release Oral [Delivery] System) is a controlled release oral drug delivery system in the form of a tablet. The tablet has a rigid water-permeable jacket with one or more laser drilled small holes.Avoidance reactionAcute myeloid dendritic cell leukemia: Acute myeloid dendritic cell leukemia is an exceedingly rare form of leukemia. This form of leukemia represents only about 0.Gross pathology: Gross pathology refers to macroscopic manifestations of disease in organs, tissues, and body cavities. The term is commonly used by anatomical pathologists to refer to diagnostically useful findings made during the gross examination portion of surgical specimen processing or an autopsy.Proinflammatory cytokine: A proinflammatory cytokine is a cytokine which promotes systemic inflammation.Conditioned place preference: Conditioned place preference (CPP) is a form of Pavlovian conditioning used to measure the motivational effects of objects or experiences. This paradigm can also be used to measure conditioned place aversion with an identical procedure involving aversive stimuli instead.
(1/5750) Lymph node germinal centers form in the absence of follicular dendritic cell networks.
Follicular dendritic cell networks are said to be pivotal to both the formation of germinal centers (GCs) and their functions in generating antigen-specific antibody affinity maturation and B cell memory. We report that lymphotoxin beta-deficient mice form GC cell clusters in the gross anatomical location expected of GCs, despite the complete absence of follicular dendritic cell networks. Furthermore, antigen-specific GC generation was at first relatively normal, but these GCs then rapidly regressed and GC-phase antibody affinity maturation was reduced. Lymphotoxin beta-deficient mice also showed substantial B cell memory in their mesenteric lymph nodes. This memory antibody response was of relatively low affinity for antigen at week 4 after challenge, but by week 10 after challenge was comparable to wild-type, indicating that affinity maturation had failed in the GC phase but developed later. (+info)
(2/5750) Selective recruitment of CCR4-bearing Th2 cells toward antigen-presenting cells by the CC chemokines thymus and activation-regulated chemokine and macrophage-derived chemokine.
Helper T cells are classified into Th1 and Th2 subsets based on their profiles of cytokine production. Th1 cells are involved in cell-mediated immunity, whereas Th2 cells induce humoral responses. Selective recruitment of these two subsets depends on specific adhesion molecules and specific chemoattractants. Here, we demonstrate that the T cell-directed CC chemokine thymus and activation-regulated chemokine (TARC) was abundantly produced by monocytes treated with granulocyte macrophage colony stimulating factor (GM-CSF) or IL-3, especially in the presence of IL-4 and by dendritic cells derived from monocytes cultured with GM-CSF + IL-4. The receptor for TARC and another macrophage/dendritic cell-derived CC chemokine macrophage-derived chemokine (MDC) is CCR4, a G protein-coupled receptor. CCR4 was found to be expressed on approximately 20% of adult peripheral blood effector/memory CD4+ T cells. T cells attracted by TARC and MDC generated cell lines predominantly producing Th2-type cytokines, IL-4 and IL-5. Fractionated CCR4+ cells but not CCR4- cells also selectively gave rise to Th2-type cell lines. When naive CD4+ T cells from adult peripheral blood were polarized in vitro, Th2-type cells selectively expressed CCR4 and vigorously migrated toward TARC and MDC. Taken together, CCR4 is selectively expressed on Th2-type T cells and antigen-presenting cells may recruit Th2 cells expressing CCR4 by producing TARC and MDC in Th2-dominant conditions. (+info)
(3/5750) Cytotoxic T-cell responses in mice infected with influenza and vaccinia viruses vary in magnitude with H-2 genotype.
Secondary effector T-cell populations generated by cross-priming with heterologous influenza A viruses operate only in H-2K or H-2D compatible situations, when assayed on SV40-transformed target cells infected with a range of influenza A viruses. The H2-Kb allele is associated with a total failure in the generation of influenza-immune cytotoxic T cells, though this is not seen for the primary response to vaccinia virus. In both influenza and vaccinia development of effector T cells operating at H-2Db is greatly depressed in B10.A(2R) (kkkddb) and B10.A(4R) (kkbbbb), but not in B10 (bbbbbb), mice. However, there is no defect in viral antigen expression at either H-2Kk or H-2Db in B10.A(2R) target cells. This apparently reflects some inadequacy in the stimulator environment, as (A/J X B6) F1 T cells can be induced to respond at H-2Db when exposed to vaccinia virus in an irradiated B6 but not in a B10.A(4R) recipient. The present report, together with the accompanying paper by Zinkernagel and colleagues, records the first rigorous demonstration of both a nonresponder situation and a probable Ir-gene effect for conventional infectious viruses. Possible implications for the evolution of H-2 polymorphism and mechanisms of Ir gene function are discussed. (+info)
(4/5750) Core 2-containing O-glycans on CD43 are preferentially expressed in the memory subset of human CD4 T cells.
Human CD4 T cells can be divided into two functionally distinct subsets: a CD45RO+ memory subset and a CD45RA+ naive subset. In an attempt to identify novel cell surface molecules on these cells, we have developed a mAb, anti-1D4. The antigen defined by anti-1D4 was preferentially expressed on the memory subset of freshly isolated peripheral CD4 T cells and 1D4+ CD4 T cells functionally corresponded to memory T cells. Retrovirus-mediated expression cloning revealed that the 1 D4 antigen is human CD43. Transfection of CHO-leu cells, which stably express human CD43, with core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT) conferred expression of the 1D4 antigen and mRNA of C2GnT was detected by RT-PCR only in 1D4+ T cells but not in 1D4- T cells, implying that the 1 D4 antigen is composed of core 2-containing O-glycans on CD43. Reactivity with anti-1 D4 was completely abolished when cells were treated with neuraminidase, while them remained weak binding of anti-T305, a previously described mAb which also reacts with CD43 modified with core 2-containing O-glycans. Moreover, anti-1D4 markedly reacted with NIH-3T3 cells expressing human CD43 and low levels of endogenous C2GnT, whereas anti-T305 reacted slightly. These results indicate that the 1D4 antigen is distinct from the epitope defined by anti-T305 and anti-1D4 is a more sensitive probe to detect core 2-containing O-glycans than anti-T305. Taken together, our results indicate that core 2-containing O-glycans, whose expression can easily be detected with anti-1D4, are preferentially expressed in the CD45RO+ memory subset of CD4 T cells. (+info)
(5/5750) Enhanced cytotoxic T cell activity in IL-4-deficient mice.
CD8+ effectors are critical components of type 1 responses against viral infections as well as for antiviral vaccines. IL-4 plays a clear role as an inhibitor of CD4+ Th1 cells; however, its role in CD8+ T cell regulation appears to be more complex. Thus, IL-4 may augment CD8+ T cell growth, but also limit effector function. Moreover, abundant IL-4 is inhibitory for viral clearance, but the lack of IL-4 appears not to affect CTL-mediated immunity. This report investigates these disparate roles of IL-4 in CD8+ T lymphocyte regulation by comparing T cell responses specific for a single HIV-IIIIB gp120-derived epitope in BALB/c mice deficient in IL-4 to those in wild-type controls. CTL activation was monitored during the acute and memory phases following immunization with recombinant vaccinia virus. Similar frequencies of gp120-specific CTL precursors in splenocytes from both groups indicated that IL-4 plays no significant role in either CTL priming or the establishment of memory. However, cytolytic activity in cultures derived from IL-4-deficient mice developed earlier and was strikingly enhanced following in vitro restimulation, an effect exhibited by both primary and memory T cells. Secretion of IL-2 and IFN-gamma by CD8+ T cells from IL-4-deficient mice was also elevated, reflecting their enhanced activation. Thus, IL-4 appears to limit the activation, expansion, and differentiation of CD8+ T cells with high cytolytic potential. (+info)
(6/5750) Linear differentiation of cytotoxic effectors into memory T lymphocytes.
A central question in immunology is the origin of long-lived T cell memory that confers protection against recurrent infection. The differentiation of naive T cell receptor transgenic CD8+ cells into effector cytotoxic T lymphocytes (CTLs) and memory CD8+ cells was studied. Memory CD8+ cells that were generated after strong antigenic stimulation were the progeny of cytotoxic effectors and retained antigen-specific cytolytic activity 10 weeks after adoptive transfer to antigen-free recipient mice. Thus, potential vaccines based on CTL memory will require the differentiation of naive cells into post-effector memory T cells. (+info)
(7/5750) Functional differences between memory and naive CD8 T cells.
To determine how murine memory and naive T cells differ, we generated large numbers of long-lived memory CD8(+) T cells and compared them to naive cells expressing the same antigen-specific receptor (T cell receptor; TCR). Although both populations expressed similar levels of TCR and CD8, on antigen stimulation in vitro memory T cells down-regulated their TCR faster and more extensively and secreted IFN-gamma and IL-2 faster than naive T cells. Memory cells were also larger, and when freshly isolated from mice they contained perforin and killed target cells without having to be restimulated. They further differed from naive cells in requiring IL-15 for proliferation and in having a greater tendency to undergo apoptosis in vitro. On antigen stimulation in vivo, however, they proliferated more rapidly than naive cells. These findings suggest that, unlike naive T cells, CD8 memory T cells are intrinsically programmed to rapidly express their effector functions in vivo without having to undergo clonal expansion and differentiation. (+info)
(8/5750) Postthymic development of CD28-CD8+ T cell subset: age-associated expansion and shift from memory to naive phenotype.
During human aging, one of the major changes in the T cell repertoire is a dramatic expansion of T cells with the atypical CD28-CD8+ phenotype. In this study, we show that this increase is a consequence not only of an expansion in the CD28-CD8+ population but also of a decrease in the number of CD28+CD8+ T cells. The decrease in circulating CD28+CD8+ T cells is dramatically accelerated after the age of 50 and is not accompanied by an equivalent reduction in the CD28+CD8+ subset. Our findings confirm that aging leads to an accumulation of CD45RO+ T cells within the CD28+CD8+ subset as previously observed. Surprisingly, we found an increase in CD45RA+ expression with age in the CD28-CD8+ subset. Immune-phenotyping for activation markers, measurement of telomere DNA content, and cytokine production analysis indicate that the large majority of CD28-CD8+ T cells are Ag-experienced, despite their CD45RA+ phenotype. Our study further demonstrates that the poor proliferative response displayed by CD28-CD8+ T cells is not a consequence of telomere shortening. Also, analysis of cytokine production at the single cell level revealed that the proportions of IFN-gamma +, IL-4+, and IL-10+ T cells are considerably higher among the CD28-CD8+ than the CD28+CD8+ subset. In summary, these data explain the presence of CD45RA+ T cells in the elderly, shed light on the phylogenetic origin of CD28-CD8+ T cells, and suggest a role for these cells in the immune senescence process. (+info)