acquired immunity
The kind of defense that is mediated by B lymphocytes (B cells) and T lymphocytes (T cells). It exhibits specificity, memory, and self-nonself recognition. Also called adoptive immunity.
active immunity
Long-lasting immunity conferred by the action of a person's B cells and T cells and the resulting B and T memory cells specific for a pathogn. It can develop as a result of natural infection or immunization.
anaphylactic shock
An acute, whole-body, life-threatening, allergic response.
antibody
A protein secreted by plasma cells (differentiated B cells) that binds to a particular antigen and marks it for elimination; also called immunoglobulin. All antibody molecules have the same Y-shaped structure and in their monomer form consist of two ident
antigen
A macromolecule that elicits an immune response by lymphocytes.
antigen presentation
The process by which an MHC molecule binds to a fragment of an antigen and carries it to the cell surface, where it is displayed and can be recognized by a T cell.
antigen receptor
The general term for a surface protein, located on B cells and T cells, that binds to antigens, initiating acquired immune responses. The antigen receptors on B cells are called B cell receptors (or membrane immunoglobulins), and the antigen receptors on
antigen-presenting cell
A cell that ingests bacteria and viruses and destroys them, generating peptide fragments that are bound by class II MHC molecules and subsequently displayed on the cell surface to helper T cells. Macrophages, dendritic cells, and B cells are the primary a
apoptosis
The changes that occur within a cell as it undergoes programmed cell death, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die.
autoimmune disease
An immunological disorder in which the immune system turns against self.
B lymphocyte (B cell)
A type of lymphocyte that develops to maturity in the bone marrow. After encountering antigen, B cells differentiate into antibody-secreting plasma cells, the effector cells of humoral immunity.
cell-mediated immune response
The branch of acquired immunity that involves the activation of cytotoxic T cells, which defend against infected cells, cancer cells, and transplanted cells.
chemokin
Any of about 50 different proteins, secreted by many cell types near a site of injury or infection, that help direct migration of white blood cells to an injury site and induces other changes central to inflammation.
clonal selection
The process by which an antigen selectively binds to and activates only those lymphocytes bearing receptors specific for the antigen. The selected lymphocytes proliferate and differentiate into a clone of effector cells and a clone of memory cells specifi
cytokine
Any of a group of proteins secreted by a number of cell types, including macrophages and helper T cells, that regulate the function of lymphocytes and other cells of the immune system.
epitope
A small, accessible region of an antigen to which an antigen receptor or antibody binds; also called an antigenic determinant.
helper T cell
A type of T cell that, when activated, secretes cytokines that promote the response of B cells (humoral response) and cytotonic T cells (cell-mediated response) to antigens.
histamine
A substance released by mast cells that causes blood vessels to dilate and become more permeable during an inflammatory response.
humoral immune response
The branch of acquired immunity that involves the activation of B cells and that leads to the production of antibodies, which defend against bacteria and viruses in body fluids.
innate immunity
The kind of defense that is mediated by phagocytic cells, antimicrobial proteins, the inflammatory response, and natural killer (NK) cells. It is present before exposure to pathogens and is effective from the time of birth.
interferon
A protein that has antiviral or immune regulatory functions.it is secreted by virus-infected cells, help nearby cells resist viral infection; and is secreted by T cells in order to help activate macrophages.
lysozyme
An enzyme in sweat, tears, and saliva that attacks bacterial cell walls.
macrophage
A phagocytic cell present in many tissues that functions in innate immunity by destroying microbes and in acquired immunity as an antigen-presenting cell.
major histocompatibility complex (MHC)
A family of genes that encode a large set of cell surface proteins. The molecules function in antigen presentation to T cells.
mast cell
A vertebrate body cell that produces histamine and other molecules that trigger the inflammatory response.
memory cell
One of a clone of long-lived lymphocytes, formed during the primary immune response, that remains in a lymphoid organ until activated by exposure to the same antigen that triggered its formation. Once activated, these cells mount the secondary immune resp
natural killer (NK) cell
A type of white blood cell that can kill tumor cells and virus-infected cells; an important component of innate immunity.
neutrophil
The most abundant type of white blood cell. Neutrophils are phagocytic and tend to self-destruct as they destroy foreign invaders, limiting their life span to a few days.
passive immunity
Short-term immunity conferred by the administration of ready-made antibodies or the transfer of maternal antibodies to a fetus or nursing infant; lasts only a few weeks or months because the immune system has not been stimulated by antigens.
phagocytosis
A type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells.
primary immune response
The initial acquired immune response to an antigen, which appears after a lag of about 10 to 17 days.
secondary immune response
The acquired immune response elicited on second or subsequent exposures to a particular antigen. The secondary immune response is more rapid, of greater magnitude, and of longer duration than the primary immune response.
T lymphocyte (T cell)
A type of lymphocytethat develops to maturity in the thymus. After encountering antigen, these cells are responsible for cell-mediated immunity.
thymus
A small organ in the thoracic cavity of vertebrates where maturation of T cells is completed.