Active immunotherapy: A treatment for cancer whichmakes the assumption that if the immune system ot apatient could be activated (e.g., by engineering dendriticcells to express tumor antigens), it could then destroy histumor.ADCC: Antibody-dependent cellular cytotoxicity.Antibodies bind to the target, and Fc receptors on thesurfaces of cytotoxic cells (e.g., macrophages or NK cells)bind to the Fc portion of the antibodies to form a"bridge" between the target and the cytotoxic cell:antibody-directed ki l l ing by cells of the innate system.Allergen: An antigen that causes allergies.Anergize: To "neuter" - to render nonfunctional.Anergy: A state of nonfunctionality.Antigen: A rather loosely used term for the target (e.g.,a viral protein) of an antibody or a T cell. To be moreprecise, an antibody binds to a region of an antigen calledthe epitope, and the T cell receptor binds to a peptidethat is a fragment of an antigen.Anti oncogene: A gene that encodes a tumorsuppressor protein.APC: Antigen presenting cell - cells like activatedmacrophages, activated dendritic cells, and activatedB cells that can present antigen efficiently to T cells viaMHC molecules, and which can supply theco-stimulatory molecules required to activate T cells.Apoptosis: The process during which cells commitsuicide in response to problems within the cell or tosignals from outside the cell.Autocrine: A fancy word for "self" (e.g., autocrinestimulation is self-stimulation).BCR: B cell receptor.β2 microglobulin: The nonpolymorphic chain of theclass I MHC molecule.Central memory cells: Memory B or T cells that residein the secondary lymphoid organs and proliferate slowly.

The progeny of these B cells resupply long-lived plasmaB cells which have died of old age. If there is a secondattack, central memory cells quickly produce short-livedplasma B cells (which produce tons of antibodies) andeffector T cells (which travel to the tissues to participatein the battle).Central tolerance induction: Process by which T cellswith receptors that recognize abundant self antigens inthe thymus are anergized or deleted.Chemokine: A special cytokine that is used to directcells to their proper positions.Clonal selection principle: When receptors on B orT cells recognize their cognate antigen, these cells aretriggered (selected) to proliferate. As a result, a clone of Bor T cells with identical antigen specificities is produced.Cognate antigen: The antigen (e.g., a bacterial protein)which a B or T cell's receptors recognize and bind to.Co-receptor: The CD4 or CD8 molecules on T cells, orthe complement receptor on B cells. Ligation of theco-receptors amplifies the signal sent through the B andT cell receptors.Cortical thymic epithelial cell: Cells in the cortex ofthe thymus which are the "examiners" during positiveselection (MI IC restriction) of T cells which recognizeMHC-peptide complexes.Co-stimulation: The second "key" that B and T cellsneed for activation.Cross-link: Cluster together (e.g., an antigen maycross-link a B cell's receptors).Cross-reacts: Recognizes several different epitopes. Forexample, a B cell's receptors may bind to (cross-readwith) several different epitopes that are present onseveral different antigens.CTL: Cytotoxic lymphocyte - synonym for killer T cell.Cytokine profile: The mixture of different cytokinesthat a cell secretes.

Cytokines: I lormone-like messenger molecules thatcells use to communicate.Cytoplasm: The l iquid portion of a cell in which theorganelles and the nucleus "float."Dendritic cell (DC): A starfish-shaped cell which,when activated by battle signals, travels from the tissuesto the secondary lymphoid organs to present antigen tonaive T cells.DTH: Delayed type hypersensitivity. An inflammatoryreaction in which Th cells recognize a specific invader, AND secrete cytokines that activate and recruit innatesystem cells to do the ki l l ing.Endocytosis: Similar to phagocytosis except that itbegins when the th ing being "eaten" binds to a receptoron the surface of the phagocytic cell: receptor-initiatedphagocytosis.Endogenous protein: A protein that is producedw i t h i n the cell in question - the opposite of an exogenousprotein.

Endoplasmic reticulum (ER): A large sack-likestructure inside the cell from which most proteinsdestined tor transport to the cell surface begin the i rjourney.Endothelial cells: Cells shaped like shingles that linethe insides of our blood vessels.Epithelial cells: Cells that form part of the barrier thatseparates our bodies from the outside world.Epitope: The region of an antigen that is recognized by a13 or T cell's receptors.Exogenous protein: A protein that is outside thecell in question - the opposite of an endogenous protein.Follicular dendritic cell (FDC): A starfish-shaped cellthat retains opsonized antigens in germinal centers, anddisp lays these antigens for B cells.Germinal center: An area in a secondary lymphoidorgan in which 13 cells proliferate, undergo somaticIn permutation, and switch classes. Also known as a"secondary lymphoid follicle."He: I leavy chain protein oi the antibody molecule.High endothelial venule (HEV): A region in a bloodvessel where there are high endothelial cells which allowlymphocytes to exit the blood.IFN-γ: Interferon gamma - a cytokine secreted mainly bvTh I helper T cells and NK cells.Inducible regulatory T cells. CD4+T cells which,when stimulated repeatedly bv an invader, can producecytokines that negatively regulate the immune responseout in the tissues.

Inflammatory response: A rather general termthat describes the b a t t l e that macrophages, neutrophils,and other immune system cells wage against aninvader.Interleukin (IL): A protein (cytokine) that is used forcommunication between leukocytes (e.g., IL-2).Isotype: A svnonvm for A lass." The isotvpe ol anantibody (e.g., IgA or IgG) is determined by the constantregion of its heavy chain.Lc: Light chain protein of the antibody molecule.Leukocytes: A generic term that includes all of thedifferent kinds of while blood cells.Ligand: A molecule that binds to a receptor (e.g., the hasligand binds to the Fas receptor protein on the surface ofa cell).

Ligate: Hind to. When a receptor has bound its ligand,the receptor is said to be "ligated."Lipopolysaccharide (LPS): A component ol manybacterial cell walls which serves as a "danger signal" forthe innate system.Lymph: The l iquid that "leaks" out of blood vessels intothe tissues.Lymphocyte: The generic term for a B cell or a T cell.Lymphoid follicle: A region of a secondary lymphoidorgan that contains follicular dendritic cells embedded ina sea of B cells.M cell: A cell that crowns a Fever's patch, and whichspecializes in sampling antigen from the intestine.MALT: Mucosal-associated lymphoid tissues. Secondarylymphoid organs that are associated with mucosa (e.g.,Peyer's patches and tonsils).Medullary thymic epithelial cell: A cell in themedulla of the thymus which expresses tissue-specificself antigens, and which takes part in the examination ofT cells for tolerance of self (negative selection).Memory effector T cells: Memory T cells that liedormant in the tissues until an enemy attacks again.MHC proteins: Proteins encoded by the majorhistocompatibility complex (the region ol a chromosomethat includes a "complex" of genes involved in antigenpresentition).MHC restriction: Survival in the thymus is "restricted"to T cells whose receptors recognize antigen presented byMHC molecules.Microbe: A generic term that includes bacteria andviruses.Monocytes: White blood cells that are the precursors ofmacrophages or dendritic cells.

Mucosa: The tissues and associated mucus that protectexposed surfaces such as the gastrointestinal andrespiratory tracts.Naive lymphocytes: B or T cells which have never beenactivated.Natural regulatory T cells (nTregs): CD4+ T cellsthat are selected in the thymus and which negativelyregulate the immune response by interfering with theactivation of self-reactive T cells in the secondarylymphoid organs.Necrosis: Cell death, typically caused by burns or othertrauma. This type of cell death (as opposed to apoptoticcell death) usually results in the contents of the cellbeing dumped into the tissues. This can cause tissuedamage.Negative selection: Synonym for "central toleranceinduction, "the selection of T cells whose receptors donot recognize MHC-self peptide complexes in thethymus.NK cell: Natural killer cell - a player on the innatesystem team.Oncogene: A mutated proto-oncogene which encodes aprotein that can cause cells to proliferate inappropriately.Opsonize: "Decorate" with fragments of complementproteins or with antibodies.Passive immunotherapy: A treatment for cancer inwhich immunologists attempt to engineer a patient'scells (e.g., his killer T cells) to be "super killers" which,when returned to his body, can destroy his tumor.Pathogen: A disease-causing agent (e.g., a bacterium ora virus).Peptide: A small fragment of a protein, usually onlytens of amine) acids in length.Peripheral tolerance: The mechanisms that induceself-tolerance outside the thymus.Phagocytes: Cells such as macrophages andneutrophils that engulf (phagoevtose) invaders.Plasma B cells: Short-lived plasma B cells produce alarge burst of antibodies in response to an attack and die.

Long-lived plasma 13 cells make more modest amounts ofantibodies that confer long-term protection.Positive selection: Synonym for "MHC restriction."Primary lymphoid organs: The thymus and the bonemarrow.Proliferate: Increase in number. A cell proliferates bydividing into two daughter cells, which then can divideagain to give four cells, and so on. Cellular reproduction.Proteasome: A multiprotein complex in the cell thatchops proteins up into small pieces.Proto-oncogene: A gene which, if mutated, canbecome an oncogene.Secondary lymphoid organs: Organs such as lymphnodes, Peyer's patches, and the spleen where activationof naive B and T cells takes place.Secrete: Export out of the cell (e.g., cytokines aresecreted by the T cells that produce them, and B cellssecrete antibodies).TCR: T cell receptor.Th: Helper T cell.Thymic dendritic cell: A cell found in the medulla ofthe thymus which administers the exam for tolerance ofself (negative selection) to T cells.TNF: Tumor necrosis factor - a cytokine secreted mainlyby macrophages and helper T cells.Tolerance: Not viewing self as an attacker which shouldbe targeted for destruction.Tolerize: To make a B cell or T cell tolerant of our selfantigens.Toll-like receptors (TLRs): Receptor molecules foundeither on the surface of cells or inside cells. Thesereceptors have evolved to recognize the signatures ofcommon invaders and to generate signals which alert theimmune system to danger.Tumor suppressor protein: A protein which is part ofa control system within a cell that safeguards againstinappropriate cell proliferation.Virgin (naive) lymphocytes: B or T cells which havenever been activated.