AP Bio Chapter 43

Immune System

secondary immune response

adaptive immune response elicited on second or subsequent exposures to a particular antigen which is more rapid, of greater magnitude, and of longer duration than the primary immune response.

passive immunity

Short-term immunity conferred by the transfer of antibodies, as occurs in the transfer of maternal antibodies to a fetus or nursing infant.

lymphocyte

A type of white blood cell that mediates immune responses. The two main classes are B cells and T cells.

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.

antibody

A protein secreted by plasma cells (differentiated B cells) that binds to a particular antigen; also called immunoglobulin. All antibodies have the same Y-shaped structure and in their monomer form consist of two identical heavy chains and two identical light chains, immunoglobulin(Ig)

natural killer cell

A type of white blood cell that can kill tumor cells and virus-infected cells as part of innate immunity.

Toll-like receptor (TLR)

A membrane receptor on a phagocytic white blood cell that recognizes fragments of molecules common to a set of pathogens.

antigen-presenting cell

A cell that upon ingesting pathogens or internalizing pathogen proteins generates peptide fragments that are bound by class II MHC molecules and subsequently displayed on the cell surface to T cells. Macrophages, dendritic cells, and B cells are the primary antigen-presenting cells.

complement system

A group of about 30 blood proteins that may amplify the inflammatory response, enhance phagocytosis, or directly lyse extracellular pathogens.

dendritic cell

An antigen-presenting cell, located mainly in lymphatic tissues and skin, that is particularly efficient in presenting antigens to helper T cells, thereby initiating a primary immune response.

monoclonal antibody

Any of a preparation of antibodies that have been produced by a single clone of cultured cells and thus are all specific for the same epitope.

inflammatory response

An innate immune defense triggered by physical injury or infection of tissue involving the release of substances that promote swelling, enhance the infiltration of white blood cells, and aid in tissue repair and destruction of invading pathogens.

HIV (human immunodeficiency virus)

The infectious agent that causes AIDS, a retrovirus.

B cells

The lymphocytes that complete their development in the bone marrow and become effector cells for the humoral immune response.

antigen presentation

The process by which an MHC molecule binds to a fragment of an intracellular protein antigen and carries it to the cell surface, where it is displayed and can be recognized by a T cell.

phagocytosis

A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).

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 specific for the stimulating antigen.

autoimmune disease

An immunological disorder in which the immune system turns against self.

active immunity

Long-lasting immunity conferred by the action of B cells and T cells and the resulting B and T memory cells specific for a pathogen. Active immunity can develop as a result of natural infection or immunization.

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.

immune system

An organism's system of defenses against agents that cause disease.

interferon

A protein that has antiviral or immune regulatory functions. For example, interferons secreted by virus-infected cells help nearby cells resist viral infection.

humoral immune response

The branch of adaptive 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.

heavy chain

One of the two types of polypeptide chains that make up an antibody molecule and B cell receptor; consists of a variable region, which contributes to the antigen-binding site, and a constant region.

histamine

A substance released by mast cells that causes blood vessels to dilate and become more permeable in inflammatory and allergic responses.

antigen

A substance that elicits an immune response by binding to receptors of B or T cells.

acquired immunodeficiency syndrome (AIDS)

The symptoms and signs present during the late stages of HIV infection, defined by a specified reduction in the number of T cells and the appearance of characteristic secondary infections.

light chain

One of the two types of polypeptide chains that make up an antibody molecule and B cell receptor; consists of a variable region, which contributes to the antigen-binding site, and a constant region.

cytotoxic T cell

A type of lymphocyte that, when activated, kills infected cells as well as certain cancer cells and transplanted cells.

epitope

A small, accessible region of an antigen to which an antigen receptor or antibody binds.

adaptive immunity

A vertebrate-specific defense that is mediated by B lymphocytes (B cells) and T lymphocytes (T cells) and that exhibits specificity, memory, and self-nonself recognition; also called acquired immunity.

antigen receptor

The general term for a surface protein, located on B cells and T cells, that binds to antigens, initiating adaptive immune responses. The antigen receptors on B cells are called B cell receptors, and the antigen receptors on T cells are called T cell receptors.

cell-mediated immune response

The branch of adaptive immunity that involves the activation of cytotoxic T cells, which defend against infected cells.

innate immunity

A form of defense common to all animals that is active immediately upon exposure to a pathogen and that is the same whether or not the pathogen has been encountered previously.

primary immune response

The initial adaptive immune response to an antigen, which appears after a lag of about 10−17 days.

immunization

The process of generating a state of immunity by artificial means. In vaccination, an inactive or weakened form of a pathogen is administered, inducing B and T cell responses and immunological memory. In passive immunization, antibodies specific for a particular pathogen are administered, conferring immediate but temporary protection.

thymus

A small organ in the thoracic cavity of vertebrates where maturation of T cells is completed.

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. Activated memory cells mount the secondary immune response.

T cells

The class of lymphocytes that mature in the thymus; they include both effector cells for the cell-mediated immune response and helper cells required for both branches of adaptive immunity.

pathogen

An organism or virus that causes disease.

major histocompatibility complex (MHC) molecule

host protein that functions in antigen presentation. Foreign MHC molecules on transplanted tissue can trigger T cell responses that may lead to rejection of the transplant.

lysozyme

An enzyme that destroys bacterial cell walls; in mammals, it is found in sweat, tears, and saliva.

helper T cell

A type of T cell that, when activated, secretes cytokines that promote the response of B cells (humoral response) and cytotoxic T cells (cell-mediated response) to antigens.

effector cell

A lymphocyte that has undergone clonal selection and is capable of mediating an adaptive immune response.