Innate and Adaptive Body Defenses: The Immune System

A comprehensive set of vocabulary flashcards covering the innate and adaptive defense systems, cell types, inflammatory processes, and immune system imbalances from Chapter 21 of the lecture notes.

Immunity

Resistance to disease, derived from the word 'immun' meaning free.

Innate (nonspecific) defense system

A functional system that responds within minutes to protect the body from all foreign substances; consists of surface barriers and internal defenses.

Adaptive (specific) defense system

The body's third line of defense that attacks particular foreign substances and takes more time to mount than the innate response.

Pathogens

Harmful or disease-causing microorganisms.

First line of defense

The external body membranes consisting of intact skin and mucosae.

Acid mantle

The acidity of skin, vaginal, and stomach secretions that inhibits bacterial growth.

Lysozyme

An enzyme found in saliva, respiratory mucus, and lacrimal fluid of the eye that destroys bacteria.

Mucin

A substance that, when dissolved in water, forms thick, sticky mucus that traps microorganisms in digestive and respiratory passageways.

Defensins

Broad-spectrum antimicrobial peptides secreted by mucous membranes and skin that disrupt microbial membranes.

Second line of defense

Internal defenses including antimicrobial proteins, phagocytes, and other cells used when the first line has been penetrated; hallmark is inflammation.

Neutrophils

The most abundant type of white blood cell that becomes phagocytic upon encountering infectious material in tissues.

Macrophages

Voracious phagocytic cells, or 'big eaters,' that derive from monocytes that leave the bloodstream and enter tissues.

Stellate macrophages

Fixed macrophages that are permanent residents of the liver.

Phagocytosis

The process by which a phagocyte engulfs particulate matter into a membrane-lined vesicle called a phagosome.

Opsonization

The process of coating pathogens with opsonins (complement proteins or antibodies) to provide 'handles' that accelerate phagocytosis.

Respiratory burst

A process where helper T cells stimulate macrophages to produce lethal oxidizing chemicals and free radicals like superoxide and $H_2O_2$ to kill pathogens.

Natural killer (NK) cells

A unique group of large granular lymphocytes that can lyse and kill cancer cells and virus-infected cells before the adaptive immune system is activated.

Apoptosis

Programmed cell death, the method used by NK cells and cytotoxic T cells to kill targets.

Inflammatory response

A tissue response to injury that prevents the spread of damaging agents, disposes of debris, and sets the stage for repair; signaled by redness, heat, swelling, and pain.

Histamine

A potent inflammatory chemical released by the granules of mast cells and basophils.

Toll-like receptors (TLRs)

Surface membrane receptors on macrophages that recognize particular classes of attacking microbes and trigger the release of cytokines.

Hyperemia

Congestion with blood that occurs when local arterioles dilate, accounting for the redness and heat of inflammation.

Exudate

Fluid containing clotting factors and antibodies that seeps from the blood into tissue spaces during inflammation.

Leukocytosis

An increase in the number of white blood cells in the bloodstream, characteristic of inflammation.

Margination

The phenomenon of phagocytes clinging to the inner walls (margins) of capillaries and postcapillary venules.

Diapedesis

The process where neutrophils flatten and squeeze between the endothelial cells of capillary walls.

Chemotaxis

The movement of white blood cells up a gradient of inflammatory chemicals (chemotactic agents) to the site of injury.

Pus

A creamy yellow mixture of dead or dying neutrophils, broken-down tissue cells, and living and dead pathogens.

Interferons (IFNs)

Small proteins secreted by virus-infected cells that diffuse to nearby cells to stimulate the synthesis of proteins that block viral replication.

Complement

A group of at least $20$ plasma proteins (C1 through C9, factors B, D, and P) that circulate in the blood and amplify all aspects of the inflammatory process.

Membrane attack complex (MAC)

A group of complement proteins that insert into a target cell's membrane, creating a hole that allows an influx of water and lyses the cell.

Pyrogens

Chemicals released by leukocytes and macrophages that act on the hypothalamus to raise body temperature above $37^{\circ}\text{C}$ ($98.6^{\circ}\text{F}$).

Humoral immunity

Also called antibody-mediated immunity, it is provided by antibodies circulating in the body's fluids.

Cellular immunity

Also called cell-mediated immunity, it is provided by living lymphocytes that act against targets directly or indirectly.

Antigens

Substances that can mobilize the adaptive defenses and provoke an immune response; contracted from 'antibody generating.'

Immunogenicity

The ability of an antigen to stimulate specific lymphocytes to proliferate.

Reactivity

The ability of an antigen to react with activated lymphocytes and antibodies.

Hapten

An incomplete antigen that is reactive but not immunogenic unless attached to a protein carrier; found in poison ivy, animal dander, and some drugs.

Antigenic determinants

Specific parts of an antigen molecule that are immunogenic and where antibodies or lymphocyte receptors bind.

MHC proteins

Self-antigen glycoproteins, coded for by the major histocompatibility complex, that identify a cell as 'self.'

Immunocompetence

The ability of a lymphocyte to recognize its one specific antigen by binding to it.

Self-tolerance

The requirement that each lymphocyte be relatively unresponsive to self-antigens to avoid attacking the body's own cells.

Positive selection

The T cell education test that ensures only T cells able to recognize self-MHC proteins survive.

Negative selection

The T cell education test that ensures T cells do not recognize self-antigens displayed on self-MHC, forming the basis of self-tolerance.

Antigen-presenting cells (APCs)

Cells that engulf antigens and present fragments of them on their own surfaces for T cells to recognize; include dendritic cells, macrophages, and B cells.

Dendritic cells

Mobile sentinels found at the body's frontiers (like skin) that are the most effective antigen presenters known.

Plasma cells

The antibody-secreting effector cells of the humoral response, capable of secreting antibodies at a rate of $2000$ molecules per second.

Antibody titer

The concentration of antibodies in the plasma.

Antibodies (Immunoglobulins)

Proteins secreted by plasma cells that bind specifically with an antigen; divided into classes IgM, IgA, IgD, IgG, and IgE.

Variable (V) region

The region at one end of both heavy and light antibody chains that combines to form the antigen-binding site.

Constant (C) region

The stem region of an antibody monomer that determines the antibody class and its effector functions.

Neutralization

A defensive mechanism where antibodies block specific sites on viruses or bacterial exotoxins, preventing them from binding to tissue cells.

Agglutination

The clumping of foreign cells that occurs when antibodies cross-link cell-bound antigens; IgM is a potent agent of this.

Hybridomas

Cell hybrids made by fusing tumor cells and B lymphocytes, used to produce pure monoclonal antibodies.

Helper T (TH) cells

Effector CD4 T cells central to both humoral and cellular immunity that activate B cells, T cells, and macrophages.

Cytotoxic T (TC) cells

Effector CD8 T cells that directly attack and kill other cells like virus-infected or cancerous body cells.

Regulatory T (TReg) cells

A population of T cells that dampen the immune response to prevent autoimmune reactions.

Anergy

A state of unresponsiveness to an antigen that occurs when a T cell binds to an antigen without receiving co-stimulatory signals.

Cytokines

Chemical messengers of the immune system, including interferons and interleukins, that influence cell development and differentiation.

Autografts

Tissue grafts transplanted from one body site to another in the same person.

Isografts

Grafts donated to a patient by a genetically identical individual, such as an identical twin.

Allografts

Grafts transplanted from individuals belonging to the same species who are not genetically identical.

Xenografts

Grafts taken from another animal species.

Severe combined immunodeficiency (SCID) syndromes

Congenital disorders resulting from genetic defects that produce a marked deficit of B and T cells.

Acquired immune deficiency syndrome (AIDS)

A condition caused by HIV that cripples the immune system by interfering with the activity of helper T cells.

Autoimmunity

The condition where the body produces antibodies and cytotoxic T cells that destroy its own tissues.

Systemic lupus erythematosus (SLE)

A systemic autoimmune disorder affecting young females that targets kidneys, blood vessels, brain, and joints; often identified by a 'butterfly rash.'

Anaphylactic shock

A rare, systemic allergic response that can cause life-threatening circulatory collapse and constriction of the bronchioles.