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Chapter 2 - Cells and Organs of the Immune System


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a white blood cell;
the category includes lymphocytes, granulocytes, platelets, monocytes, and macrophages
Hematopoietic stem cell (HSC)
the cell type from which all lineages of blood cells arise
Stem cells
a cell from which differentiated cells arise
the formation and differentiation of blood cells
Lymphoid progenitor cell
a cell committed to the lymphoid lineage from which all lymphocytes arise
Myeloid progenitor cell
a cell that gives rise to cells of the myeloid lineage
Progenitor cells
a cell that has lost the capacity for self renewal and is committed to the generation of a particular cell lineage
any of numerous secreted, low molecular weight proteins that regulate the intensity and duration of the immune response by exerting a variety of effects on lymphocytes and other immune cells
Stromal cells
a nonhematopoietic cell that supports the growth and differentiation of hematopoietic cells
Hematopoietic-inducing microenvironment (HIM)
an anatomical site that contains all of the cells and cellular factors required for the generation and development of blood cells
Colony-stimulating factors (CSFs)
proteins that are able to induce and support the growth and development of distinct hematopoietic cell lines
Erythropoietin (EPO)
a cytokine that induces the commitment of progenitor cells to the erythroid lineage
GATA-2 gene
a gene encoding a transcription factor that is essential for the development of several hematopoietic cell lineages, including the lymphoid, erythroid and myeloid lineages
a transcription factor required for the development of all lymphoid cell lineages
Programmed cell death
an induced and ordered process in which the cell actively participates in bringing about its own death
morphologic changes associated with programmed cell death, including nuclear fragmentation, blebbing, and release of apoptotic bodies, which are phagocytosed;
in contrast to necrosis, it does not result in damage to surrounding cells
Differentiation antigen
a cell-surface marker that is expressed only during a particular developmental stage or by a particular cell lineage
Natural killer cells
a class of large granular cytotoxic lymphocytes that do not have T- or B-cell receptors;
antibody-independent killers of tumor cells and also can participate in ADCC
a proliferating lymphocyte
Naive lymphocytes
denoting mature B and T cells that have not encountered antigen;
synonymous with unprimed and virgin
Effector cells
any cell capable of mediating an immune function (e.g., activated T(H) cells, CTLs, and plasma cells)
Memory cells
lymphocytes generated following encounters with antigen that are characteristically long lived; they are more readily stimulated than naive lymphocytes and mediate a secondary immune response to subsequent encounters with the antigen
Plasma cells
the antibody-secreting effector cell of the B lineage
Cluster of differentiation (CD)
a collection of monoclonal antibodies that all recognize an antigen found on a particular differntiated cell type or types; each of the antigens recognized by such a collection of antibodies is called a CD marker and assigned a unique identifying number
T(H)1 response
this response produces a cytokine profile that supports inflammation and cell mediated responses;
antagonistic to the T(H)2 response
T(H)2 response
this response produces a cytokine profile that activates mainly immune responses that depend upon antibodies;
antagonistic to the T(H)1 response
Cytotoxic T lymphocyte (CTL)
an effector T cell (usually CD8+) that can mediate the lysis of target cells bearing antigenic peptides complexed with an MHC molecule;
usually arises from an antigen-activated T(C) cell
T suppressor cells
a population of T cells postulated to be distinct from T(H) and T(C)cells that suppress the humoral and cell-mediated branches of the immune system in an antigen-specific manner
Antibody-dependent cell-mediated cytotoxicity (ADCC)
a cell-mediated reaction in which nonspecific cytotoxic cells that express Fc receptors (e.g., NK cells, neutrophils, macrophages) recognize bound antibody on a target cell and subsequently cause lysis of the target cell
NK1-T cell
a lymphocyte with some of the characteristics of T cells (it has TCRs) as well as those of NK cells
a mononuclear phagocytic leukocyte that circulates briefly in the bloodstream before migrating into the tissues where it becomes a macrophage
mononuclear phagocytic leukocytes that play roles in adaptive and in innate immunity;
some are migratory and others are fixed in tissues
directional movement of cells up the concentration gradient
membrane protrusions that extend from motile and phagocytosing cells
intracellular vacuole containing ingested particulate materials;
formed by the fusion of pseudopodia around a particle undergoing phagocytosis
a small cytoplasmic vesicle found in many types of cells that contains hydrolytic enzymes, which play an important role in the degradation of material ingested by phagocytosis and endocytosis
an intracellular body formed by the fusion of a phagosome with a lysosome
process by which cells release molecules (e.g., cytokines, lytic enzymes, degradation products) contained within a membrane-bound vesicle by fusion of the vesicle with the plasma membrane
a substance that promotes the phagocytosis of antigens by binding to them
deposition of opsonins on an antigen, thereby promoting a stable adhesive contact with an appropriate phagocytic cell
Reactive oxygen intermediates (ROIs)
highly reactive compounds such as superoxide anion, hydroxyl radicals, and hydrogen peroxide that are formed under many conditions in cells and tissues
Reactive nitrogen intermediates
highly cytotoxic antimicrobial compounds formed by the combination of oxygen and nitrogen within phagocytes such as neutrophils and macrophages
Respiratory burst
a metabolic process in activated phagocytes in which the rapid uptake of oxygen is used to produce reactive oxygen intermediates that are toxic to ingested microorganisms
Nitric Oxide synthetase
an enzyme that synthesizes nitric oxide from the amino acid L-arginine
Nitric oxide
a gas that plays important roles in intercellular signaling
an enzyme present in tears, saliva, and mucous secretions that digests mucopeptides in bacterial cell walls and thus functions as a nonspecific antibacterial agent
cysteine-rich, positively charged, antimicrobial peptides that contain 25-35 amino acids and are found in macrophages and neutrophils
Tumor necrosis factors (TNFs)
two related cytokines produced by marophages and some T cells;
cytotoxic to tumor cells but not to normal cells;
also play a role in inflammatory response
a group of serum proteins that participates in an enzymatic cascade, ultimately generating the cytolytic membrane attack complex
any leukocyte that contains cytoplasmic granules, particularly the basophil, eosinophil, and neutrophil
a circulating, phagocytic granulocyte involved early in the inflammatory response;
expresses Fc receptors and can participate in antibody-dependent cell-mediated cytotoxicity;
the most numerous WBCs in the circulation
motile, somewhat phagocytic granulocytes that can migrate from blood to tissue spaces;
have large numbers of IgE receptors and are highly granular; that to play a role in the defense against parasitic organisms such as roundworms
a nonphagocytic granulocyte that expresses Fc receptors for IgE;
antigen-mediated cross-linkage of bound IgE induces degranulation of basophils
an abnormally large number of leukocytes, usually associated with acute infection;
counts greater than 10,000/cc may be considered leukocytosis
movement of blood cells through an unruptured vessel wall into the surrounding tissue, particularly at sites of inflammation
Chemotactic factor
an agent that can cuase leukocytes to move up its concentration gradient
Dendritic cell
bone-marrow derived cells that descend through the myeloid and lymphoid lineages and are specialized for antigen presentation to helper T cells
Follicular dendritic cell
a cell with extensive dendritic extensions that is found in the follicles of lymph nodes;
although they do not express MHC-II molecules, they are richly endowed with receptors for complement and Fc receptors for antibody;
of a lineage that is distinct from MHC-II bearing dendritic cells
Primary lymphoid organs
organs in which lymphocyte precursors mature into antigenically committed, immunocompetent cells;
in mammals, the bone marrow and thymus are the primary lymphoid organs in which B-cell and T-cell maturation occur, respectively
Secondary lymphoid organs
organs and tissues in which mature, immunocompetent lymphocytes encounter trapped antigens and are activated into effector cells;
in mammals, the lymph nodes, spleen, and MALT constitue the secondary lymphoid organs
Tertiary lymphoid tissues
tissues that normally contain few lymphoid cells, lack the elaborate organization of secondary lymphoid tissue, and import lymphoid cells during an inflammatory response
Lymphatic system
a network of vessels and nodes that convey lymph;
returns plasma-derived interstitial fluids to the blood stream and plays an important role in the integration of the immune system
denoting a mature lymphocyte that is capable of recognizing a specific antigen and mediating an immune response
a primary lymphoid organ, located in the thoracic cavity, where T-cell maturation takes place
Bone marrow
the living tissue found within the hard exterior of bone
Interstitial fluid
fluid found in the space between cells of an organ or tissue
interstitial fluid derived from blood plasma that contains a variety of small and large molecules, lymphocytes, and some other cells;
circulates through the lymphatic vessels
Lymphatic vessels
thinly walled vessels through which the fluid and cells of the lymphatic system moves through the lymph nodes and ultimately into the thoracic duct, where it joins the blood stream
Thoracic duct
the largest of the lymphatic vessels; returns lymph to the circulation by emptying into the left subclavian vein near the heart
Primary follicle
a lymphoid follicle, prior to stimulation with antigen, that contains a network of follicular dendritic cells and small resting B cells
Secondary follicle
a primary follicle after antigenic stimulation;
develops into a ring of concentrically packed B-cells surrounding a germinal center
Germinal center
a region within lymph nodes and the spleen where B-cell activation, proliferation, and differentiation occurs;
sites of intense B cell somatic mutation and selection
Lymph nodes
a small secondary lymphoid organ that contains lymphocytes, macrophages, and dendritic cells and serves as a site for filtration of foreign antigen and for activation and proliferation of lymphocytes
secondary lymphoid organ where old erythrocytes are destroyed and blood-borne antigens are trapped and presented to lymhocytes in the PALS and marginal zone
Red pulp
portion of the spleen consisting of a network of sinusoids populated by macrophages and erythrocytes;
the site where old and defective red blood cells are destroyed
White pulp
portion of the spleen that surrounds the arteries, forming a periarteriolar lymphoid sheath populated mainly by T cells
Mucosal-associated lymphoid tissue (MALT)
lymphoid cells and tissues below the epithelial layer of the body's mucosal surfaces;
found in the gastrointestinal and reproductive tracts
nodular structures containing a meshwork of reticular cellsand fibers that contain lymphocytes, macrophages, granulocytes, and mast cells;
defend the body against antigens entering through nasal or oral routes
Intraepithelial lymphocytes
T cells found in the epithelial layer of organs and the GI tract
M cells
specialized cells of the intestinal mucosa and other sites, such as the urogential tract, that deliver antigen from the apical face of the cell to lymphocytes clustered in the pocket of its basolateral face
Inductive site
small regions of a mucus membrane that lie over organized lymphoid follicles and contain M cells

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