Chapter 43 - The Immune System

Question 1

immune system

Answer 1

An animal body’s system of defenses against agents that cause disease.

Question 2

innate immunity

Answer 2

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

Question 3

adaptive immunity

Answer 3

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

Question 4

lysozyme

Answer 4

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

Question 5

phagocytosis

Answer 5

A type of endocytosis in which large particulate substance 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).

Question 6

Toll-like receptor (TLR)

Answer 6

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

Question 7

neutrophil

Answer 7

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.

Question 8

macrophage

Answer 8

A phagocytic cell present in many tissues that functions in innate immunity by destroying microbes and in acquired immunity as an antigen-presenting cell.

Question 9

dendritic cell

Answer 9

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.

Question 10

natural killer cell

Answer 10

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

Question 11

interferon

Answer 11

A protein that has antiviral or immune regulatory functions. Interferon-α and interferon-β, secreted by virus-infected cells, help nearby cells resist viral infection; interferon-γ, secreted by T cells, helps activate macrophages.

Question 12

complement system

Answer 12

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

Question 13

inflammatory response

Answer 13

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.

Question 14

histamine

Answer 14

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

Question 15

mast cell

Answer 15

A vertebrate body cell that produces histamine and other molecules that trigger inflammation in response to infection and in allergic reactions.

Question 16

cytokine

Answer 16

Any of a group of small proteins secreted by a number of cell types, including macrophages and helper T cells, that regulate the function of other cells.

Question 17

lymphocyte

Answer 17

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

Question 18

thymus

Answer 18

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

Question 19

T cells

Answer 19

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.

Question 20

B cells

Answer 20

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

Question 21

antigen

Answer 21

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

Question 22

antigen receptor

Answer 22

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.

Question 23

epitope

Answer 23

A small, accessible region of an antigen to which an antigen receptor or antibody binds; also called an antigenic determinant.

Question 24

heavy chain

Answer 24

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.

Question 25

light chain

Answer 25

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.

Question 26

antibody

Answer 26

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.

Question 27

immunoglobulin (Ig)

Answer 27

Any of the class of proteins that function as antibodies. Immunoglobulins are divided into five major classes that differ in their distribution in the body and antigen disposal activities.

Question 28

major histocompatibility complex (MHC) molecule

Answer 28

A 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.

Question 29

antigen presentation

Answer 29

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.

Question 30

effector cell

Answer 30

(1) A muscle cell or gland cell that performs the body’s response to stimuli as directed by signals from the brain or other processing center of the nervous system. (2) A lymphocyte that has undergone clonal selection and is capable of mediating an adaptive immune response.

Question 31

memory cell

Answer 31

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.

Question 32

clonal selection

Answer 32

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 simulating antigen.

Question 33

primary immune response

Answer 33

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

Question 34

secondary immune response

Answer 34

The adaptive 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.