Immunity: the condition of being protected against an infectious disease. Immunity can be caused by a vaccine, previous infection with the same agent, or by transfer of immune substances from another person or animal. (NCI1) Non-susceptibility to the invasive or pathogenic effects of foreign microorganisms or to the toxic effect of antigens. (MeSH)

Provides the ability of an animal to ward off internal threats such as “bacteria,” the presence of foreign molecules, and the presence of abnormal cells (such as “cancer” cells). (Brooker, 1127) "Innate immunity" against "infection" is due to relatively nonspecific cellular and molecular systems that protect the organism against bacteria or "viruses" and is present in most animals and in plants. 'Lifelong immunity' to a particular disease is a result of an adaptive "immune response" and may be acquired naturally by previous infection or is induced by "vaccination" with suitably treated "microorganisms." (Lawrence) Autoimmunity is the body’s immune system directing an attack against itself. (Leschziner, 116)

Allergy: a reaction of your “immune system” to something that does not bother most other people. People who have allergies often are sensitive to more than one thing. (MedlinePlus) An immune system response to a substance that does not actually present a threat. (Lewis, 337) A hypersensitive “immune reaction” to a substance that normally is harmless or would not cause an immune response in most people. An allergic response may cause harmful symptoms such as itching or “inflammation” or “tissue” injury. (NCI1) In a person with allergies, the immune response is oversensitive. When it recognizes an “allergen,” the immune system launches a response. Chemicals such as “histamines” are released. These chemicals cause allergy symptoms. Common allergens include drugs, dust, food, insect venom, mold, pet and other animal dander, and pollen (PubMedHealth2) Adjective - ‘allergic.’ Also referred to as ‘type 1 hypersensitivity,’ ‘allergic response,’ and ‘allergic reaction.’

Antibodies: components of the immune system that circulate in the “blood,” recognize foreign substances like bacteria and viruses, and neutralize them. After exposure to a foreign substance, called an "antigen," antibodies continue to circulate in the blood, providing protection against future exposures to that antigen. (NHGRI) Produced by "B cells," (they) bind a specific foreign antigen, alerting the immune system or destroying the antigen. (Lewis, G-1) The way in which these molecules work is closely related to their structure. (Indge, 19) Also referred to as ‘immunoglobulin.’

Antigen Binding Site: tip of the ‘variable region’ of the antibody (where the antigen binding takes place). (Lewis, 331)

Antigen: a foreign substance which, when introduced into the body, stimulates the production of an antibody. (Oxford) Any molecules that can elicit an “immune response.” (Lewis, 326) Substances that are recognized by the immune system and induce an immune reaction. (MeSH) Any substance that causes your immune system to produce antibodies against it. An antigen may be a foreign substance from the environment such as chemicals, bacteria, viruses, or pollen. An antigen may also be formed within the body, as with bacterial “toxins" or tissue cells. (PubMedHealth2) Adjective - ‘antigenic.’

Autoimmunity: process whereby the immune system reacts against the body's own tissues. Autoimmunity may produce or be caused by "autoimmune disorders." (MeSH) The immune system produces antibodies that attack the body’s own tissues. (Lewis, 336)

Cytokines: non-antibody proteins, secreted by “white blood cells” and some non-white blood cells, that act as intercellular mediators. They differ from classical “hormones” in that they are produced by a number of tissue or cell types rather than by specialized glands. (MeSH) "Helper T-cells" secrete, interact with, and signal each other. (Lewis, 332) Any protein or "polypeptide" produced by a cell and which affects the growth or "differentiation" of the same or another cell. Examples are... 'differentiation factors,' "growth factors," and "interleukins." (Lawrence)

Interferons: substances that can improve the body's natural response to infections and other diseases. Interferons interfere with the division of cancer cells and can slow “tumor” growth. There are several types of interferons, including ‘interferon-alpha, -beta, and -gamma.’ The body normally produces these substances. They are also made in the laboratory to treat cancer and other diseases. (NCI1) Secreted by cells in response to a wide variety of “inducers.” They confer “resistance” against many different viruses, inhibit proliferation of normal and “malignant” cells, impede multiplication of intracellular “parasites,” and augment “natural killer cell” activity. (MeSH) 

Interleukins: factors which stimulate growth-related activities of (white blood cells) as well as other cell types. They enhance cell proliferation and differentiation, secretion of other biologically active molecules, and responses to immune and inflammatory stimuli. (MeSH) One of a group of related proteins made by white blood cells and other cells in the body. Regulate immune responses. Interleukins made in the laboratory are used as biological response ‘modifiers’ to boost the immune system in cancer therapy. (NCI1) Also referred to as ‘IL.’

Cytotoxicity: attacking or destroying cells. (Lawrence) Cell killing. (NCIt) The phenomenon of target cell destruction by immunologically active cells. (MeSH) Adjective - 'cytotoxic.'

Detoxify: render a toxic substance harmless. (Lawrence) Remove poison from; free from poisonous quantities. (Oxford)

Immune Response: how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful. (PubMedHealth2) The activity of the immune system against foreign substances. (NCI1) The immune response attacks pathogens, cancer cells, and transplanted cells with two lines of defense - an immediate generalized “innate immunity,” and a more specific, slower “adaptive immunity.” (Lewis, 328) Protection from an infectious disease agent that is mediated following exposure to a specific antigen, and characterized by ‘immunologic’ memory. It can result from either previous infection with that agent or vaccination, or transfer of an antibody or lymphocyte from an immune donor. (MeSH) Also referred to as ‘immune system response’ and ‘adaptive immunity.”

Cellular Immune Response: production of cytotoxic and helper T cells. (Lawrence) In this response, helper T cells stimulate B cells to manufacture antibodies and “cytotoxic T cells” to secrete cytokines. Using T cell “receptors,” cytotoxic T cells bind to ‘non-self’ cells and virus-covered cells and burst them. (Lewis, 333)

Humoral Immune Response: antibody-mediated immune response. Humoral immunity is brought about by antibody formation. (MeSH) In this response, a antigen-presenting “macrophage” activates a helper T cell. The helper T cell activates B cells with matching cell surface receptors. B cells divide to produce "plasma cells" and "memory cells'. Plasma cells secrete antibodies into blood that will recognize the antigen presented. Memory cells remain dormant until a second exposure (to the same antigen), after which they respond faster and more effectively. (Lewis, 330-331) Also referred to as ‘humoral immunity.’

Immune System: the cells and organs within an animal’s body that contribute to immune defenses. (Brooker, 1127) Body system that produces specialized white blood cells that protect the body from viruses, bacteria, and tumor cells. (Hockenbury, 484) Protects the body from possibly harmful substances by recognizing and responding to antigens. The immune system recognizes and destroys substances that contain antigens. (PubMedHealth2) The body's defense mechanism against foreign organisms or substances and deviant native cells. It consists of a complex of interrelated cellular, molecular, and genetic components. (MeSH) Includes white blood cells and organs and tissues of the “lymph system,” such as the “thymus,” “spleen,” "tonsils," "lymph nodes," "lymph vessels," and “bone marrow.” (NCI1)

Immunoassay: test that uses the binding of antibodies to antigens, to identify and measure certain substances. Immunoassays may be used to diagnose disease. Also, test results can provide information about a disease that may help in planning treatment (for example, when estrogen receptors are measured in breast cancer). (NCI1)

Immunocompromised: individuals that have any of the following: are receiving active cancer treatment for tumors or cancers of the blood; have received an organ transplant and are taking medicine to suppress the immune system; have received a stem cell transplant within the last two years or are taking medicine to suppress the immune system; have moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome); have advanced or untreated HIV infection; have active treatment with high-dose corticosteroids or other drugs that may suppress the immune response. (CDC)

Immunotoxin: an antibody linked to a toxic substance. Some immunotoxins can bind to cancer cells and kill them. (NCI1) Toxic molecules with specific immune substances such as antibodies and antigens. The immune substance carries the toxin to the “tumor” or infected cell where the toxin exerts its poisonous effect. (MeSH)

Innate Immunity: the defense system with which (humans are) born. It protects against all antigens. Innate immunity involves barriers that keep harmful materials from entering (the) body. These barriers form the first line of defense in the immune response. Examples of innate immunity include cough reflex, enzymes in tears and skin oils, mucus, which traps bacteria and small particles, skin, and stomach acid. (PubMedHealth2)

Lymph System: a group of organs and tissues composed primarily of "lymphatic vessels." (Brooker, 1131) A network of organs, lymph nodes, lymph ducts, and lymph vessels that make and move “lymph” from tissues to the bloodstream. (PubMedHealth2) A series of vessels or channels within the body that drain fluid from the tissues back into the circulation. Roughly three litres of fluid pass through this system a day, helping to remove waste substances and toxins from the tissues, but also flowing through lymph glands to faciliate the immmune system. Damage to the lymphatic system after surgery for breast cancer, for example, can cause ‘lymphoedema,’ swelling fo the arm due to inadequate drainage of this fluid. An infection in the foot may cause lymph glands in the groin to swell, as the immune system kicks in to fight that infection and the lymph node enlarges in response. (Leschziner, 86) The lymph system is a major part of the body's immune system. It includes the tonsils, adenoids, spleen, and thymus. (PubMedHealth2) Also referred to as ‘lymphatic system.’

Lymph: a fluid that travels through the lymphatic system and carries cells that help fight infections and other diseases. (NCI1) Filters out of "capillaries" into the spaces of the body and eventually returns to the "circulatory system." (Brooker, 1131) A colorless fluid, resembling blood but lacking red cells, which bathes various tissues and organs of the body and drains into the bloodstream through the lymphatic system. (Oxford) Made of cells that attack bacteria in the blood. (PubMedHealth2) Also referred to as ‘lymphatic fluid.’

Lymph Nodes: any of several small masses of tissue situated on the “lymphatic vessels,” responsible for removing foreign bodies from the lymph and for producing lymphocytes and antibodies. (Oxford) A rounded mass of lymphatic tissue that is surrounded by a capsule of connective tissue. Lymph nodes filter lymphatic fluid, and they store white blood cells. They are located along lymphatic vessels. (NCI1) Within a lymph node, lymph percolates through open cavities containing clusters of lymphocytes (Brooker, 1132) Soft, small, round- or bean-shaped structures. They usually cannot be seen or easily felt. Located in clusters in various parts of the body, such as the neck, armpit, groin, and inside the center of the chest and abdomen. Make immune cells that help the body fight infection. They also filter the lymph fluid and remove foreign material such as bacteria and cancer cells. When bacteria are recognized in the lymph fluid, the lymph nodes make more infection-fighting white blood cells, which causes the nodes to swell. The swollen nodes are sometimes felt in the neck, under the arms, and groin. (PubMedHealth2) Also referred to as ‘lymph glands.’

Lymphocytes: a type of immune cell that is made in the “bone marrow” and is found in the blood and in lymph tissue. (NCI1) Specialized white blood cells that are responsible for immune defenses. (Hockenbury, 484) White blood cells formed in the body's lymphoid tissue. The “nucleus” is round or ovoid with coarse, irregularly clumped “chromatin” while the “cytoplasm” is typically pale blue. Most lymphocytes can be classified as either ’T’ or ‘B.’ (MeSH) Adjective - ‘lymphoid.’

B-Cells: cells maturing within bone marrow. (Brooker, 1132) Lymph cells concerned with ‘humoral’ immunity. They are short-lived cells, (engaged in the) production of immunoglobulin upon appropriate stimulation. (MeSH) Make antibodies. (NCI1) Divide and differentiate into “plasma cells” and “memory cells.” (Lewis, 333) Also referred to as ‘B-Lymphocytes.’

Memory Cells: respond to a foreign antigen faster and with more force should it appear again. This is the “secondary immune response.” (Lewis, 331)

Plasma Cells: cells differentiating from B-cells. Synthesize and secrete antibodies that bind to and help destroy foreign molecules. (Brooker, 1131) Antibody factories, each secreting 1,000 to 2,000 identical antibodies per second into the bloodstream. They live only days. They provide the “primary immune response.” (Lewis, 330)

Natural Killer Cells: bone marrow-derived lymphocytes that possess cytotoxic properties, classically directed against transformed and virus-infected cells. Unlike T Cells and B Cells, (natural killer cells) are not antigen specific. (MeSH) Attack cancer cells and cells infected with viruses without recognizing antigens. (Lewis, 334)

T-Cells: the immune system’s foot soldiers in the constant battle against invading bacteria and viruses. (Goleman, 5) A type of white blood cell. T-cells are part of the immune system and develop from stem cells in the bone marrow. They help protect the body from infection and may help fight cancer. (NCI3) Named because they mature within the “thymus.” They directly kill infected, mutated, or transplanted cells. (Brooker, 1131) Lymphocytes responsible for cell-mediated immunity. Two types have been identified - cytotoxic T-cells and helper T-cells. They are formed when lymphocytes circulate through the thymus gland and (are) differentiated. When exposed to an antigen, they divide rapidly and produce large numbers of new T-cells sensitized to that antigen. (MeSH) Also referred to as ’T-lymphocytes,’  ‘thymocytes,’ and ‘thymus-dependent lymphocytes.’ Editor's note - not found in the brain.

Cytotoxic T-Cells: T-lymphocytes that can kill cells and are the means of destroying virus-infected cells in an adaptive immune response. (Lawrence) Travel to the location of their targets, bind to these targets by combining with an antigen, and directly kill those targets via secreted chemicals. (Brooker, 1131) Attack virally infected and cancerous cells by attaching to them and releasing chemicals. (Lewis, 333) Also referred to as ‘cytotoxic T-lymphocytes.’

Helper T-Cells: assist in the activation and function of B-Cells and cytotoxic T-Cells. Do not themselves function as attack cells. (Brooker, 1131) Also referred to as ‘helper T-lymphocytes.’

Perforin: a protein, released by T-cells,  which pierces the cancer cell’s plasma membrane, killing it. (Lewis, 333) Synthesized in white blood cells and sequestered in (“secretory vesicles”). Upon immunological reaction between a white blood cell and a target cell, perforin is released at the plasma membrane which leads to death of the target cell. (MeSH)

Thermocyte: immature T-Cell. (Lewis, 332)

Lymph Vessels: network of vessels that drain the fluid known as lymph. (Brooker, 1131) Tubular vessels that are involved in the transport of lymph and lymphocytes. (MeSH) Also referred to as ‘lymphatic vessels.’

Macrophage: immune system cell that originates in the bone marrow and migrates into the blood. Engulfs bacteria and stimulates “helper T cells” to proliferate and activate B cells. (Lewis, 329) A type of white blood cell that surrounds and kills microorganisms, removes dead cells, and stimulates the action of other immune system cells. (NCI1 ) Derives from white blood cells that have entered tissues. Ingests and destroys invading microorganisms and also scavenges dead and damaged cells and cellular debris. (Lawrence)

Tonsils: one of two small masses of lymphoid tissue on either side of the throat. (NCIt) Also referred to as ‘palatine tonsil.’

Resistance: consists of activities of biologic molecules or complexes involved in processes that maintain immunity to, or counteract, defeat, or withstand the effects of, an antagonistic agent. (NCIt) Editor’s note - now, more commonly referred to as ‘resistance process.’