adaptive immunity response of antigen-specific B and T lymphocytes to antigen, including the development of immunological memory ADCC/antibody-dependent cell mediated cytotoxicity the killing of antibody-coated target cells by NK cells having the F-c-gamma-R-III receptor (CD16) that recognizes the Fc region of the bound antibody adenoid mucosa-associated secondary lymphoid tissues located in the nasal cavity afferent lymphatic vessel the several vessels that bring draining from connective tissue into a lymph node en route to the blood alpha, gamma, delta, mu, kappa, lambda chains xx antibody the secreted form of the immunoglobulin made by a B cell antibody affinity how well the antibody binds its antigen antibody valence Number of identical antigen binding sites per molecule antigenic determinant epitope B cell lymphocytes that are dedicated to making immunoglobulin and antibodies BALT bronchial associated lymphoid tissue basophil white blood cell present in small numbers in the blood, which is one of three types of granulocyte. They contain granules that stain with basic dyes. BCR/B cell receptor the antigen receptor on B cells. Each B cell is programmed to make a single type of immunoglobulin. The cell surface form of this immunoglobulin serves as the BCR for specific antigen. Associated in the membrane with the immunoglobulin are the signal transduction molecules Ig-alpha and beta. bone marrow The tissue in the center of certain bones that is the major site of generation of al the cellular elements of blood (hematopoiesis). Bruton's disease X-linked agammaglobulinemia Bruton's tyrosine kinase/Btk Defect in the gene for it causes XLA cell-mediated immunity (cellular immunity) any adaptive immune response in which antigen-specific effector T cells dominate. It is defined operationally as all adaptive immunity that cannot be transferred to a naive recipient with serum antibody. clonal expansion the process of clonal selection by selected lymphocytes clonal selection The central principle of adaptive immunity. The mech by which adaptive immune responses derive only from individual antigen-specific lymphocytes which are stimulated by the antigen to proliferate and diffferentiation into antigen-specific effector cells. complement activation the initiation by pathogens of a series of reactions involving the complement components of plasma, leading to the death and elimination of the pathogen. complementarity determining region/CDR the localized regions of immunoglobulin and T-cell receptor chains that determine the antigenic specificity and bind to the antigen. The CDRs are the most variable parts of the variable domains and are also called hypervariable regions. constant region/domain/C region the part of an immunoglobulin or T-cell receptor (or of its constituent polypeptide chains) that is of identical amino-acid sequence in molecules of the same isotype but different antigen-binding specificities. cytokines proteins made by cells that affect the behavior of other cells. Cytokines made by lymphocytes are often called lymphokines or interleukins. Cytokines bind to specific receptors on their target cells. cytotoxic T cell T cells that can kill other cells. Almost all cytotoxic T cells are CD8 T cells. Cytotoxic T cells are important in host defense against viruses and other cytosolic pathogens, because they recognize and kil the infected cells. dendritic cell Professional antigen presenting cells with a branched, dendritic morphology. They are the most potent stimulators of T-cell repsonses. They are derived from the bone marrow and are distinct from the follicular dendritic cell that presents antigen to B cells. Mature dendritic cells are present in secondary lymphoid tissues and are able to stimulate T-cells. effector T cell lymphocytes that can mediate the removal of pathogens from the body without the need for further differentiation efferent lymphatic vessel the single vessel in which lymph and lymphocytes leave a lymph node en route to the blood eosinophil white blood cell that is one of the three types of granulocyte. It contains granules that stain with eosin and whose contents are secreted when the cell is stimulated. They contribute chiefly to defnese against parasitic infections. epitope the portion of an antigenic molecule that is bound by an antibody or gives rise to the MHC-binding peptide that is recognized by a T-cell receptor. Also called an antigenic determinant. F(ab')2 a proteolytic fragment of IgG that consists of the two Fab arms held together by a disulfide bond. It is produced by digesting IgG with pepsin. Fab a proteolytic fragment of IgG that consists of the light chain and the amino-terminal half of the heavy chain held together by and interchain disulfide bond. It is called Fab because it is the Fragment with Antigen Binding specificity. In the intact IgG molecule, the parts corresponding to the FAb fragment are often called Fab or Fab arms. Fc A fragment of an antibody, resulting from proteolytic cleavage, that consists of the carboxy-terminal halves of the two heavy chains difsulfide-bonded to each other by the residual hinge region. Called Fc because it the first fragment to be crystallized. Fc-epsilon-R A receptor present of the surface of mast cells, basophils, and activated eosinophils that binds free IgE with very high affinity. When antigen binds to IgE and cross-links Fc-epsilon-R it causes cellular activation and degranulation. Fc-gamma-R Receptors present on various cell types that are specific for the Fc regions of IgG antibodies. There are different receptors for different subclasses of IgG. FcR Cell surface receptors for the Fc portion of some immunoglobulin isotypes. FcRB/Brambell receptor An FcR that transports IgG across epithelia and has a structure resembling an MHC class I molecule. GALT gut-associated lymphoid tissue, including the palatine tonsils, Peyer's Patches in the intestine, and layers of intraepithelial lymphocytes. germinal center area in secondary lymphoid tissue that is a site of intense B-cell proliferation, selection, maturation, and death. They form around follicular dendritic cell networks when activated B cells migrate into lymphoid follicles. germline gene configuration the organization of the immunoglobulin and T-cell receptor genes in the DNA of germ cells and in the vast majority of somatic cells that do not undergo somatic recombination. hapten a molecule that is incapable, alone, of causing the production of antibodies but which can do so when fastened to a larger antigenic molecule called a carrier. heavy chain the larger of the two component polypeptides of an immunoglobulin molecule. They come in a variety of heavy-chain classes or isotypes, each of which confers a distinctive effector function on the antibody molecule. helper T cell function to help other cell types to perform their functions. TH2 cells help B cells to produce antibody. hematopoietic stem cell stem cells that differentiate into blood cells humoral immunity immunity that is mediated by antibodies and can therefore be transferred to a non-immune recepient by serum. hybridoma Hybrid cell lines that make monoclonal antibodies of defined specificity. They are formed by fusing a specific antibody-producing B lymphocyte with a myeloma cell that grows in tissue culture and does not make any immunoglobulin chains on its own. hypervariable region Smal regions of high amino acid diversity within the variable regions of immunoglobulin and T-cell receptors. They correspond to the complement determining regions. IgAlpha, IgBeta B cell antigen receptors IgA the class of immunoglobulin having alpha heavy chains. IgA antibodies in dimeric form are the antibodies present in mucosal secretions. IgA in monomeric form is present in the blood. IgD the class of immunoglobulin having delta heavy chains. It appears as surface immunoglobulin on mature naive B cells, but its function is unknown. IgE the class of immunoglobulin having epsilon heavy chains. It is involved in allergic reactions. IgG the class of immunoglobulin having gamma heavy chains. It is the most abundant class of immunoglobulin in plasma. IgM the class of immunoglobulin having mu heavy chains. It is the first immunoglobulin to appear on the surface of B cells and the first antibody secreted during an immune response. It is secreted in pentameric form. immunization Deliberate provocation of an adaptive immune response by introducing antigen into the body. immunoglobulin The antigen binding molecules of B cells. immunoglobulin isotype Classes of immunoglobulin (i.e., IgG, IgM). The heavy chain constant region determines the effector properties of each antibody class. innate immunity The host defense mechanisms that act from the start of an infection and do not adapt to a particular pathogen. light chain The smaller of two types of polypeptide chain that make up immunoglobulins. It consists of one variable and one constant domain, and in the immunoglobulin molecule it is disulfide bonded to a heavy chain. There are two classes of light chains, kappa and lambda. lymph the mixture of extracellular fluid and cells that is carried by the lymphatic system. lymph capillary xx lymph duct xx lymph node B cell area/follicle xx lymph node T cell area/diffuse cortex/paracortex xx lymph vessel thin-walled vessels that carry lymph from tissues to secondary lymphoid tissues (but not the spleen) and from secondary lymphoid tissues to the thoracic duct. lymphoblast an immature lymphocyte lymphocyte a class of white blood cells that consist of small and large lymphocytes. The small lymphocytes bear variable cell-surface receptors for antigen and are responsible for adaptive immune responses. There are two main classes of small lymphocyte: B and T. Large granular lymphocytes are natural killer cells, of innate immunity. lymphokine Cytokines made by lymphocytes macrophage large mononuclear phagocytic cells resident in most tissues. They are derived from blood monocytes and contribute to innate immunity and early non-adaptive phases of host defense. They function as professional antigen-presenting cells and as effector cells in humoral and cell-mediated immunity. MALT mucosa-associated lymphoid tissue; includes GALT and BALT. mast cell large bone marrow derived cells found resident in connective tissues throughout the body. They contain large granules that store a variety of chemical mediators including histamine. Mast cells have a crucial role in allergic reactions. major histocompatibility complex a cluster of genes on the short arm of human chromosome 6 that encodes a set of polymorphic embrane glycoproteins called the MHC molecules, which are involved in presenting peptide antigens to T cells. memory cell general cells for lymphocytes that are responsbile for the phenomenon of immunological memory and protective immunity microenvironment in bone marrow monocolonal antibody antibodies produced by a single clone of B cells and are identical monocyte white blood cells with a bean shaped nucleus. They are the precursors of tissue macrophages. naive lymphocyte a B or T cell that has not yet encountered its specific antigen neutralization the mech by which antibodies binding to sites on pathogens prevent the growth of the pathogen and/or its entry into cells. neutrophil phagocytic WBCs that enter infected tissues in large numbers. They contain granules that stain with neutral dyes. After their entry into infected tissues, they engulf and kill extracellular pathogens in large numbers. The most abundant type of WBC. NK cell natural killer cells are large granular, cytotoxic lymphocytes that circulate in the blood, and are important in innate immunity to viruses and other intracellular pathogens and also kill certain tumor cells. They are the cytotoxic cells in ADCC. opsonization the coating of the surface of a pathogen or other particle with any molecule that makes it more readily ingested by phagocytes. pathogen An organism that can cause disease Peyer's Patch GALT present in the wall of the small intestine plasma cell terminally-differentiated B cells that secrete antibody. poly-Ig receptor A receptor present on the basolateral membrane of epithelial cells that binds polymeric immunoglobulins, especially dimeric IgA, and transports them across the epithelium by transcytosis pre-B cell B cells which have rearranged their heavy chain genes, but not their light chain genes. primary antibody response the adaptive immune response that follows after the first exposure to an antigen. primary lymphoid follicle The name given to the B-cell areas of secondary lymphoid tissues in the absence of an immune response. They contain resting B cells. pro-B cell B cell precursors which express B cell marker proteins and rearrange their heavy chains. pyogenic bacteria Extracellular encapsulated bacteria that cause the formation of pus at sites of infection secondary antibody response the adaptive immune response provoked by a second exposure to antigen. It starts sooner and building more quickly that the primary response. secondary lymphoid follicle name given to the B cell areas of secondary lymphoid tissues that are responding to antigen, and contain proliferating B cells. secretory component fragment of the poly-Ig receptor left attached to dimeric IgA after its transport across epithelial cells. somatic hypermutation the mutation that occurs at high frequency in the rearranged variable region DNA of immunoglobulin genes and T-cell receptor genes in developing B and T cells. spleen removes old or damaged RBCs; secondary lymphoid organ that responds to blood-borne pathogens and antigens. T cell Lymphocytes that develop in the thymus and are responsible for cell-mediated immunity. Their cell surface antigen receptor is called (surprise) the T-cell receptor. thymus a lymphoepithelial organ in the upper part of the middle chest just behind the breast bone, which develops T cells. tolerance When the immune system does not or cannot respond to an antigen. tonsil large aggregates of lymphoid cells lying on each side of the pharynx V gene segments Variable; encodes the first 95 or so AAs of the V domain. To produce a complete exon encoding a V domain, one V seg must be rearr to join up with a J or rearr'd DJ segment. D gene segments Diversity; short DNA seqs present in immunoglobulin heavy-chain loci and in T-cell receptors. In the rearr functional genes at these loci, a D region connects the V and J regions. J gene segments Joining; one of the types of gene segment in immunoglobulin and T-cell receptor sites that is rearr to make functional variable-region exons. C gene segments Encode the constant regions variable region/domain the part of the immunoglobulin or T-cell receptor that varies in AA sequence. It determines antigen specificity. vascular addressin Mucin-like cell adhesion molecules on endothelial cells to which some leukocyte adhesion molecules bind. They determine the selective homing of leukocytes to particular sites in the body X-linked agammaglobulinemia XLA is a genetic disorder in which B-cell development is arrested at the pre-B cell stage and neither mature B cells or antibodies are formed. The disease is due to a defect in the gene encoding the protein tyrosine kinase Btk.