Ch 43: The Immune System

Immunization

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

Pathogen

An organism or virus that causes disease

Epitope

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

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.

Secondary Immune Respnse

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.

Clonal Selection

The process by which an antigen selectivity 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.

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.

Thymus

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

Immune System

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

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).

Histamine

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

Mast Cell

Immune System cell that secretes histamine; plays role in inflammatory response and allergies.

Heavy Chain

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

Light Chain

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

Major Histocompatibility Complex (MHC) molecule

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

Lymphocyte

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

Inflammatory Resonse

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

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.

Eosinophil

Immune system cell that secretes destructive enzymes and helps defend against multicellular pathogens

Lysozyme

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

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.

Humoral Immune Respnse

The branch of adaptive immunity that involves that activation of B cells and that leads to the production of antibodies, which defend against bacteria and viruses in body fluids.

Immunoglobulin (lg)

See antibody

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.

Toll-like Receptor (TLR)

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

Effector Cell

(1) a muscle cell or gland cell that carries out 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.

Antigen

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

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.

B cells

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

Antigen Presentstion

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 T cells.

Primary Immune Response

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

Natural Killer Cells

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

Human Immunodeficiency Virus (HIV)

The infectious agent that causes AIDS (acquired immunodeficiency syndrome). HIV is a retrovirus.

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.

Cytotoxic T Cell

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

Antigen Receptor

The general term for a surface protein, located on B cells and T cells, that binds to antigens, initiating adaptive immune responses.

Nuetrophil

The most abundant type of white blood cell. Nuetrophils are phagocytic and tend to self-destruct as they destroy foreign invaders, limiting their life span to a few days.

Macrophage

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

Adaptive Immunity

A vertebrate-specific defense that is mediated by B lymphocytes and T lymphocytes and that exhibit specificity, memory and self-non-self recognition; also called acquired immunity

Monoclonal Immunity

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.

Cell-mediated Immune Response

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

Autoimmune Disease

An immunological disorder in which the immune system turns against itself 

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 triggers its formation. Activated memory cells mount the secondary immune response.

Complement System

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