Chapter 35: The Immune System

3 Steps of Clonal Selection

1 - Antigens bind to the antigen receptors of only three B cells. 2 - The selected B cell proliferates, forming a clone of identical cells bearing receptors for the antigen. 3 - Some daughter cells develop into long-lived memory cels that can respond rapidly upon subsequent exposure to the same antigen and other daughter cells develop into short lived plasma cells that secrete antibodies specific for the antigen.

3 Steps of The Inflammatory Response

1 - At the injury site, mast cells release histamines and macrophages secrete cytokines. These signaling molecules cause nearby capillaries to dilate. 2 - Capillaries widen and become more permeable, allowing fluid containing antimicrobial peptides to enter the tissue. Signals released by immune cells attract neutrophils. 3 - Neutrophils digest pathogens and cell debris at the site, and the tissue heals.

6 Steps of Phagocytosis

1 - Pseudopodia surround pathogens 2 - Pathogens are engulfed by endocytosis 3 - Vacuole forms, enclosing pathogens 4 - Vacuole and lysosome form 5 - Toxic Compounds and lysosomal enzymes destroy pathogens 6 - Debris from pathogens is released by exocytosis.

Autoimmune Disease

A disorder in which the immune system attacks the body's own molecules.

Innate Immunity

A form of rapid-response 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. Includes barrier defenses (skin, mucous membranes, secretions) or internal defenses (Phagocytic cells, natural killer cells, antimicrobial proteins, inflammatory response).

Inflammatory Response

A line of defense triggered by penetration of the skin or mucous membranes, in which small blood vessels in the vicinity of an injury dilate and "leak", enhancing the infiltration of neutrophils/other pathogen fighting cells.

Immunization

A process by which resistance to an infectious disease is induced to produce a primary immune response and immunological memory.

Phagocytosis

A process in which hemocytes (immune cells) ingest and break down bacteria and other foreign substances. Also known as "Cell Eating."

Antibody

A protein produced by some white blood cells to attack specific foreign materials. They are secreted rather then membrane bound, and it is these, rather than B cells themselves, that actually help defend against pathogens. Also known as Immunoglobulins (Ig).

Antigen Receptor

A protein that is attached to B or T cells and are used to attach to an antigen. It is specific enough to bind to just one part of one molecule from a particular pathogen. All of these made by a single B o T cell are identical.

Antigen

A protein that, when introduced in the blood, triggers the production of an antibody. Often found on the surface of pathogens, but can be defined as any foreign substance that triggers an immune response.

TLR (Toll Like Receptor)

A signaling receptor that binds to/recognizes fragments of molecules characteristic of a set of pathogens. Includes TLR3 (binds to double stranded RNA), TLR4 (recognizes lipopolysaccharide, aka a molecule found on the surface of many bacteria) , TLR5 (recognizes flaggelin, the main protein of bacterial flagella).

Epitope

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

Complement system

A system of innate immunity consisting of roughly 30 proteins in blood plasma. They circulate in an inactive state and are activated by substances on the surfaces of many microbes. Once activated, a result of a cascade of biochemical reactions occurs, which can lead to lysis (bursting) of invading cells.

Immune System

A term for the overall system (including the thymus and bone marrow and lymphoid tissues) that protects the body from foreign substances and pathogenic organisms by producing the immune response. It enables an animal to avoid or limit infections.

Allergens

A toxicant that overactivates the immune system, causing an immune response when one is not necessary. Cause of allergies.

Natural Killer Cells

A type of white blood cell that circulates throughout the body and detects the abnormal array of surface proteins characteristic of some virus-infected and cancerous cells. They then kill tumor cells and virus-infected cells by releasing chemicals that lead to cell death, NOT through engulfing them.

Neutrophils

A type of white blood cell that engulfs invading microbes and contributes to the nonspecific defenses of the body against disease. The first to aid in cuts. They circulate in the blood and are attracted by signals from infected tissues.

Lysozyme

An enzyme capable of breaking down cell walls of various bacteria under certain conditions. Found in perspiration, tears, saliva, nasal secretions, and tissue fluids.

Thymus

An immune organ located near the heart. It is the site of T cell maturation and is larger in children and adolescents.

Passive Immunity

An individual does not produce his or her own antibodies, but rather receives them directly from another source, such as mother to infant through breast milk. No memory cells.

Pathogen

An organism that causes disease- bacterium, fungus, virus, etc.

Viral Neutralization

Antibodies bind to proteins on the surface of a virus and prevent the infection of a host cell, thus neutralizing the virus.

Opsonization

Antibodies bind to toxins released in body fluids, preventing the toxins from entering host cells.

Monoclonal Antibodies

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

Activation of Complement

Antibodies work together with proteins of the complement system, which increase the effectiveness of antibody directed attacks on bacteria.

Dendritic Cells

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

Interferons

Antiviral proteins secreted by virus-infected body cells. They provide innate defense by limiting the cell to cell spread of viruses in the body and helping control viral infections such as colds and influenza.

Antigen-Presenting Cells

Cells that capture and present peptides to T cells.

Mast Cells

Cells that produces histamine and other molecules that trigger the inflammatory response. They are found in connective tissue.

Eosinophils

Discharge destructive enzymes/ phagocytes that defend against multicellular invaders, like pathogens. Often found beneath mucous membranes.

Macrophages

Found within the lymph nodes, they are large phagocytes that destroy bacteria, cancer cells, and other foreign matter in the lymphatic stream. Some migrate throughout the body while others reside in organs and tissues where they are likely to encounter pathogens. For example, some are located in the spleen.

Allergies

Hypersensitive responses to certain antigens called allergens.

Histamines

Inflammatory signaling molecules that are stored and released by the granules (vesicles) of mast cells. Once released near sites of damage, they trigger nearby blood vessels to dilate and become more permeable. They cause the symptoms of allergic reactions.

Memory Cells

Long-Lived cells that can give rise to effector cells if the same antigen (which binds to a b or t cell) is encountered later in life.

Heavy and Light Chains

Makes up the Y Shaped molecule of an antigen receptor. Four polypeptide chains, two identical of each, with disulfide bridges linking the chains together.

Antimicrobial Peptides

May be on of the most important components of innate immunity, small proteins secreted by epithelial cells that are toxic to certain bacteria, fungi, and viruses in skin, mucous membranes, neutrophils and act against a variety of microbes.

Humoral Response

Part of adaptive immunity in which B cells are activated and antibodies defend against infection in body fluids.

Cell-Mediated Response

Part of adaptive immunity in which cytotoxic T cells defend against infection in body cells.

Clonal Selection

Production of a clone of cells from a single lymphocyte. An antigen selects which lymphocyte will divide to produce a clonal population of thousands of cells specific for a particular epitope.

Effector Cells

Short-lived cells that take effect immediately against the antigen and any pathogens producing that antigen.

Cytokines

Signaling molecules that in an immune response promote blood flow to the site of injury or infection. The increased blood flow as a result causes the redness and increased skin temperatures typically associated with the inflammatory response.

TB and Pneumonia

Some diseases caused by pathogens that avoid our immune responses. The first one, a bacterium, grows and reproduces, effectively hidden from the body's innate immune defenses. The second one's outer covering hides its polysaccharide coat so it cannot be defensively recognized.

Cytotoxic T Cells

T cells, often called killer cells because they use toxic proteins to kill cells infected by viruses or other intracellular pathogens. They require signals from helper T cells and interact with an antigen-presenting cell to become active.

Adaptive Immunity

The acquired ability to recognize and destroy a pathogen or its products. Requires exposure of the immune system to the pathogen, and has a slow response. It includes the humoral response and cell mediated response.

Primary Immune Response

The adaptive immune response that occurs with the first exposure of an antigen. Peaks about 10 to 17 days after the initial exposure. During this time, selected B cells and T cells give rise to their effector forms.

Secondary Immune Response

The adaptive immune response that occurs with the second exposure of an antigen. Peaks only 2 to 7 days after exposure. Relies on the reservoir of T and B Memory cells generated following initial exposure to an antigen. There are enough antibodies present to immediately destroy the pathogen.

Immunological Memory

The capacity of the immune system to make quicker and stronger adaptive immune responses to successive encounters with an antigen. It is specific for a particular antigen and is long-lived.

Active Immunity

The defenses that arise when a pathogen infects the body.

Plasma Cells

The effector cells of B cells, which secrete antibodies.

MHC Molecule (Major Histocompatibility Complex)

The host protein that displays the antigen fragment on the cell surface in antigen presenting cells. Only on T Cells.

HIV (Human immunodeficiency virus)

The pathogen that causes aids, both escapes and attacks the adaptive immune response. It infects Helper T cells so the immune system is rendered useless.

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.

Antigen-Binding Site

The site on an immunoglobulin or T-cell receptor molecule that binds to a specific antigen.

Alpha and Beta Chains

Two different polypeptide chains that make up the antigen receptors on a T cell. They are linked by a disulfide bridge.

Lymphocytes

Types of white blood cells that activate the adaptive response. Includes T Cells and B Cells.

B Cells

White blood cells manufactured and matured in the bone marrow that create antibodies for isolating and destroying invading bacteria and viruses. Their antigen receptors bind to epitopes of intact antigens circulating in body fluids.

T Cells

White blood cells that mature in the thymus. They trigger the actions of other lymphocytes and fight off pathogens. They only bind to fragments of antigens that are displayed on the host cells surface.

Helper T-Cells

White blood cells that trigger both the humoral and cell-mediated immune responses. The signals from these cells initiate production of antibodies that neutralize pathogens and activate T cells that kill infected cells.