Overview of the Immune System - Immune Disorders - Merck Manuals Consumer Version Overview of the Immune System Overview of the Immune System By Peter J. Delves, PhD, University College London, London, UK Biology of the Immune System Overview of the Immune System The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include Microorganisms (commonly called germs, such as bacteria, viruses, and fungi) Parasites (such as worms) To defend the body against these invaders, the immune system must be able to distinguish between What belongs in the body (self) What does not (nonself or foreign) Any substances that are identified as nonself, particularly if they are perceived as dangerous (for example, if they can cause disease), stimulate an immune response in the body. Such substances are called antigens. Antigens may be contained within or on bacteria, viruses, other microorganisms, or cancer cells. Antigens may also exist on their own—for example, as food molecules or pollen. A normal immune response consists of recognizing a potentially harmful foreign antigen, activating and mobilizing forces to defend against it, and attacking it.

If the immune system malfunctions and mistakes self for nonself, it may attack the body’s own tissues, causing an autoimmune disorder, such as rheumatoid arthritis, thyroiditis, or systemic lupus erythematosus (lupus). Understanding the Immune System Antibody (immunoglobulin): A protein that is produced by B cells and that tightly binds to the antigen of an invader, tagging the invader for attack or directly neutralizing it. Antigen: Any substance that the immune system can recognize and can thus stimulate an immune response. B cell (B lymphocyte): A white blood cell that produces antibodies specific to the antigen that stimulated their production. Basophil: A white blood cell that releases histamine (a substance involved in allergic reactions) and that produces substances to attract other white blood cells (neutrophils and eosinophils) to a trouble spot. Cell: The smallest unit of a living organism, composed of a nucleus and cytoplasm surrounded by a membrane. Chemotaxis: The process of using a chemical substance to attract cells to a particular site.

Complement system: A group of proteins that are involved in a series of reactions (called the complement cascade) designed to defend the body—for example, by killing bacteria and other foreign cells, making foreign cells easier for macrophages to identify and ingest, and attracting macrophages and neutrophils to a trouble spot. Cytokines: Proteins that are secreted by immune and other cells that act as the immune system’s messengers to help regulate an immune response. Dendritic cell: A cell that is derived from white blood cells, resides in tissues, and helps T cells recognize foreign antigens. Eosinophil: A white blood cell that kills bacteria, that kills other foreign cells too big to ingest, that may help immobilize and kill parasites, that participates in allergic reactions, and that may help destroy cancer cells. Helper T cell: A white blood cell that helps B cells produce antibodies against foreign antigens, that helps killer T cells become active, and that stimulates macrophages. Histocompatibility: Literally, compatibility of tissue. Determined by human leukocyte antigens (see below) and used to determine whether a transplanted tissue or organ will be accepted by the recipient.

Human leukocyte antigens (HLA): A group of identification molecules that are located on the surface of all cells in a combination that is almost unique for each person, thereby enabling the body to distinguish self from nonself. Also called the major histocompatibility complex. Immune complex: An antibody attached to an antigen. Immune response: The reaction of the immune system to an antigen. Immunoglobulin: An antibody. Interleukin: A type of messenger (cytokine) secreted by some white blood cells to affect other white blood cells. Killer (cytotoxic) T cell: A T cell that attaches to infected cells and cancer cells and kills them. Leukocyte: A white blood cell, such as a monocyte, a neutrophil, an eosinophil, a basophil, or a lymphocyte (a B cell or T cell). Lymphocyte: The white blood cell responsible for acquired (specific) immunity, including producing antibodies (by B cells), distinguishing self from nonself (by T cells), and killing infected cells and cancer cells (by killer T cells).

Macrophage: A large cell that develops from a white blood cell called a monocyte, that ingests bacteria and other foreign cells, that helps T cells identify microorganisms and other foreign substances, and that is normally present in the lungs, skin, liver, and other tissues. Major histocompatibility complex (MHC): A synonym for human leukocyte antigens. Mast cell: A cell in tissues that releases histamine and other substances involved in inflammatory and allergic reactions. Molecule: A group of atoms chemically combined to form a unique substance. Natural killer cell: A type of white blood cell that can recognize and kill abnormal cells, such as certain infected cells and cancer cells, without having to first learn that the cells are abnormal. Neutrophil: A white blood cell that ingests and kills bacteria and other foreign cells. Phagocyte: A type of cell (such as a neutrophil or macrophage) that ingests and kills or destroys invading microorganisms, other cells, and cell fragments. Phagocytosis: The process of a cell engulfing and ingesting an invading microorganism, another cell, or a cell fragment.

Receptor: A molecule on a cell’s surface or inside the cell that can identify specific molecules, which fit precisely in it—as a key fits in its lock. Regulatory (suppressor) T cell: A white blood cell that helps end an immune response. T cell (T lymphocyte): A white blood cell that is involved in acquired immunity and that may be one of three types: helper, killer (cytotoxic), or regulatory. Disorders of the immune system occur when The body generates an immune response against itself (an autoimmune disorder—see Autoimmune Disorders ). The body cannot generate appropriate immune responses against invading microorganisms (an immunodeficiency disorder—see Overview of Immunodeficiency Disorders ). An excessive immune response to often harmless foreign antigens damages normal tissues (an allergic reaction—see Overview of Allergic Reactions ). Lines of Defense The body has a series of defenses. Defenses include physical barriers, white blood cells, and molecules such as antibodies and complement proteins. Physical barriers The first line of defense against invaders is mechanical or physical barriers: The skin The cornea of the eyes Membranes lining the respiratory, digestive, urinary, and reproductive tracts As long as these barriers remain unbroken, many invaders cannot enter the body.

If a barrier is broken—for example, if extensive burns damage the skin—the risk of infection is increased. In addition, the barriers are defended by secretions containing enzymes that can destroy bacteria. Examples are sweat, tears in the eyes, mucus in the respiratory and digestive tracts, and secretions in the vagina. White blood cells The next line of defense involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and other invaders. This defense has two parts: Innate immunity Acquired immunity Innate (natural) immunity (see also Innate Immunity ) does not require a previous encounter with a microorganism or other invader to work effectively. It responds to invaders immediately, without needing to learn to recognize them. Several types of white blood cells are involved: Phagocytes ingest invaders. Phagocytes include macrophages, neutrophils, monocytes, and dendritic cells. Natural killer cells are formed ready to recognize and kill cancer cells and cells that are infected with certain viruses. Some white blood cells release substances involved in inflammation and allergic reactions, such as histamine. Some of these cells often act on their own to destroy invaders.

In acquired (adaptive or specific) immunity (see also Acquired Immunity ), lymphocytes (B cells and T cells) encounter an invader, learn how to attack it, and remember the specific invader so that they can attack it even more efficiently the next time they encounter it. Acquired immunity takes time to develop after the initial encounter with a new invader because the lymphocytes must adapt to it. However, thereafter, response is quick. B cells and T cells work together to destroy invaders. To be able to recognize invaders, T cells need help from cells called antigen-presenting cells (such as dendritic cells—see Figure: How T Cells Recognize Antigens ). These cells ingest an invader and break it into fragments. Molecules Innate immunity and acquired immunity interact, influencing each other directly or through molecules that attract or activate other cells of the immune system—as part of the mobilization step in defense (see Activation and mobilization ).

These molecules include Cytokines (which are the messengers of the immune system—see Innate Immunity : Cytokines ) Complement proteins (which form the complement system—see Innate Immunity : Complement System ) These substances are not contained in cells but are dissolved in a body fluid, such as plasma (the liquid part of blood). Some of these molecules, including some cytokines, promote inflammation. Inflammation occurs because these molecules attract immune system cells to the affected tissue. To help get these cells to the tissue, the body sends more blood to the tissue. To carry more blood to the tissue, blood vessels expand and become more porous, allowing more fluids and cells to leave blood vessels and enter the tissue. Inflammation thus tends to cause redness, warmth, and swelling. The purpose of inflammation is to contain the infection so that it does not spread. Then other substances produced by the immune system help the inflammation resolve and damaged tissues heal. Although inflammation may be bothersome, it indicates that the immune system is doing its job. However, excessive or long-term (chronic) inflammation can be harmful. Organs The immune system includes several organs in addition to cells dispersed throughout the body.

These organs are classified as primary or secondary lymphoid organs. The primary lymphoid organs are the sites where white blood cells are produced and/or multiply: The bone marrow produces all the different types of white blood cells, including neutrophils, eosinophils, basophils, monocytes, B cells, and the cells that develop into T cells (T cell precursors). In the thymus, T cells multiply and are trained to recognize foreign antigens and to ignore the body’s own antigens. T cells are critical for acquired immunity. When needed to defend the body, the white blood cells are mobilized, mainly from the bone marrow. They then move into the bloodstream and travel to wherever they are needed. Lymphatic System: Helping Defend Against Infection The lymphatic system is a vital part of the immune system, along with the thymus, bone marrow, spleen, tonsils, appendix, and Peyer patches in the small intestine. The lymphatic system is a network of lymph nodes connected by lymphatic vessels. This system transports lymph throughout the body. Lymph is formed from fluid that seeps through the thin walls of capillaries into the body's tissues.

This fluid contains oxygen, proteins, and other nutrients that nourish the tissues. Some of this fluid reenters the capillaries and some of it enters the lymphatic vessels (becoming lymph). Small lymphatic vessels connect to larger ones and eventually form the thoracic duct. The thoracic duct is the largest lymphatic vessel. It joins with the subclavian vein and thus returns lymph to the bloodstream. Lymph also transports foreign substances (such as bacteria), cancer cells, and dead or damaged cells that may be present in tissues into the lymphatic vessels and to lymph organs for disposal. Lymph contains many white blood cells. All substances transported by the lymph pass through at least one lymph node, where foreign substances can be filtered out and destroyed before fluid is returned to the bloodstream. In the lymph nodes, white blood cells can collect, interact with each other and with antigens, and generate immune responses to foreign substances. Lymph nodes contain a mesh of tissue that is tightly packed with B cells, T cells, dendritic cells, and macrophages. Harmful microorganisms are filtered through the mesh, then identified and attacked by B cells and T cells.

Lymph nodes are often clustered in areas where the lymphatic vessels branch off, such as the neck, armpits, and groin. The secondary lymphoid organs include the Spleen Immune response: MedlinePlus Medical Encyclopedia Enzymes in tears and skin oils Mucus, which traps bacteria and small particles Skin Stomach acid Innate immunity also comes in a protein chemical form, called innate humoral immunity. Examples include the body's complement system and substances called interferon and interleukin-1 (which causes fever). If an antigen gets past these barriers, it is attacked and destroyed by other parts of the immune system. ACQUIRED IMMUNITY Acquired immunity is immunity that develops with exposure to various antigens. Your immune system builds a defense against that specific antigen. PASSIVE IMMUNITY Passive immunity is due to antibodies that are produced in a body other than your own. Infants have passive immunity because they are born with antibodies that are transferred through the placenta from their mother. These antibodies disappear between ages 6 and 12 months. Passive immunization may also be due to injection of antiserum, which contains antibodies that are formed by another person or animal.

It provides immediate protection against an antigen, but does not provide long-lasting protection. Immune serum globulin (given for hepatitis exposure) and tetanus antitoxin are examples of passive immunization. BLOOD COMPONENTS The immune system includes certain types of white blood cells. It also includes chemicals and proteins in the blood, such as antibodies, complement proteins, and interferon. Some of these directly attack foreign substances in the body, and others work together to help the immune system cells. Lymphocytes are a type of white blood cell. There are B and T type lymphocytes. B lymphocytes become cells that produce antibodies. Antibodies attach to a specific antigen and make it easier for the immune cells to destroy the antigen. T lymphocytes attack antigens directly and help control the immune response. They also release chemicals, known as cytokines, which control the entire immune response. As lymphocytes develop, they normally learn to tell the difference between your own body tissues and substances that are not normally found in your body. Once B cells and T cells are formed, a few of those cells will multiply and provide "memory" for your immune system. This allows your immune system to respond faster and more efficiently the next time you are exposed to the same antigen.

In many cases, it will prevent you from getting sick. For example, a person who has had chickenpox or has been immunized against chickenpox is immune from getting chickenpox again. Watch this video about: Immune response INFLAMMATION The inflammatory response (inflammation) occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause. The damaged cells release chemicals including histamine, bradykinin, and prostaglandins. These chemicals cause blood vessels to leak fluid into the tissues, causing swelling . This helps isolate the foreign substance from further contact with body tissues. The chemicals also attract white blood cells called phagocytes that "eat" germs and dead or damaged cells. This process is called phagocytosis. Phagocytes eventually die. Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes. Watch this video about: Phagocytosis IMMUNE SYSTEM DISORDERS AND ALLERGIES Immune system disorders occur when the immune response is directed against body tissue, is excessive, or is lacking. Allergies involve an immune response to a substance that most people's bodies perceive as harmless.

IMMUNIZATION Vaccination ( immunization ) is a way to trigger the immune response. Small doses of an antigen, such as dead or weakened live viruses, are given to activate immune system "memory" (activated B cells and sensitized T cells). Memory allows your body to react quickly and efficiently to future exposures. Watch this video about: Vaccines COMPLICATIONS DUE TO AN ALTERED IMMUNE RESPONSE An efficient immune response protects against many diseases and disorders. An inefficient immune response allows diseases to develop. Too much, too little, or the wrong immune response causes immune system disorders. An overactive immune response can lead to the development of autoimmune diseases , in which antibodies form against the body's own tissues. Complications from altered immune responses include: Allergy or hypersensitivity Innate immunity; Humoral immunity; Cellular immunity; Immunity; Inflammatory response; Acquired (adaptive) immunity Images Phagocytosis References Abbas AK, Lichtman AH, Pillai S. Properties and overview of immune responses. In: Abbas AK, Lichtman AH, Pillai S, eds. Cellular and Molecular Immunology. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 1. Craft J.

The adaptive immune system. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 46. Crow MK. The innate immune system. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 45. Firestein GS. Mechanisms of inflammation and tissue repair. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 48. Read More The Immune System: Information about Lymphocytes, Dendritic Cells, Macrophages, and White Blood Cells - What is Chemotherapy?

- Chemocare Care During Chemotherapy and Beyond The Immune System: Information about Lymphocytes, Dendritic Cells, Macrophages, and White Blood Cells The Immune system is a complex network of cells (such as lymphocytes) and organs that work together to defend the body against foreign substances (antigens) such as bacteria, a virus or tumor cell. When the body discovers such a substance several kinds of cells go into action in what is called an immune response. Below is a description of some of the cells that are part of the immune system. Lymphocytes Lymphocytes are one of the main types of immune cells. Lymphocytes are divided mainly into B and T cells. B lymphocytes produce antibodies - proteins (gamma globulins) that recognize foreign substances (antigen) and attach themselves to them. B lymphocytes (or B cells) are each programmed to make one specific antibody. When a B cell comes across its triggering antigen it gives rise to many large cells known as plasma cells. Each plasma cell is essentially a factory for producing antibody. An antibody matches an antigen much like a key matches a lock. Whenever the antibody and antigen interlock, the antibody marks the antigen for destruction.

B lymphocytes are powerless to penetrate the cell so the job of attacking these target cells is left to T lymphocytes. T lymphocytes are cells that are programmed to recognize, respond to and remember antigens. T lymphocytes (or T cells) contribute to the immune defenses in two major ways. Some direct and regulate the immune responses. When stimulated by the antigenic material presented by the macrophages, the T cells make lymphokines that signal other cells. Other T lymphocytes are able to destroy targeted cells on direct contact. Macrophages Macrophages are the body's first line of defense and have many roles. A macrophage is the first cell to recognize and engulf foreign substances (antigens). Macrophages break down these substances and present the smaller proteins to the T lymphocytes. (T cells are programmed to recognize, respond to and remember antigens). Macrophages also produce substances called cytokines that help to regulate the activity of lymphocytes. Dendritic Cells Dendritic cells are known as the most efficient antigen-presenting cell type with the ability to interact with T cells and initiate an immune response.

Dendritic cells are receiving increasing scientific and clinical interest due to their key role in the immune response and potential use with tumor vaccines. White Blood Cells There are different types of white blood cells that are part of the immune response. Neutrophils or granulocytes are the most common immune cells in the body. With an infection, their number increases rapidly. They are the major components of pus and are found around most common inflammations. Their job is to eat and destroy foreign material. Basophils and eosinophils are white blood cells that contain large granules inside the cell. They interact with certain foreign materials. Their increased activity may lead to an allergic reaction. The immune response is a coordinated effort. All of the immune cells work together, so they need to communicate with each other. They do this by secreting increased levels of a special protein molecule called cytokines that act on other cells. There are many different cytokines. Examples of these are interleukins, interferons, tumor necrosis factors, and colony-stimulating factors. Some immunotherapy treatment strategies involve giving larger amounts of these proteins by an injection or infusion.

This is done in the hope of stimulating the cells of the immune system to act more effectively or to make the tumor cells more recognizable to the immune system. Caution: There are people who promote unproven therapies as immune system boosters. Be careful when evaluating these claims. The following are types of immunotherapies that are commonly and legitimately used in traditional and scientific medical practice. More Chemotherapy Information: Antibodies, antigens, monoclonal antibodies Antibodies are "natural" chemicals produced by the body's immune system in response to infecting micro-organisms. Do not confuse antibodies with antibiotics. What is the difference between antibodies and antibiotics? Antibodies are produced by the (human/whatever) body "naturally" in response to specific "foreign" cells - bacteria or viruses. Antibiotics are produced by micro-organisms cultured by Man, then processed and administered in a general (hopeful!) way by a doctor as a drug, in order to kill or prevent the reproduction of bacteria - but they are ineffective against viruses.

More specifically, each antibody is produced by lymphocytes (specialised white cells) as a result of exposure to specific chemical substances (mainly proteins and carbohydrates ) called antigens, usually on the outside of an invading organism. This is called the antigen-antibody reaction. So-called B-cell lymphocytes produce the antibodies, in response to T-cells (there are several sorts) which participate more directly in recognising the foreign cells, and chemically damaging them. The antibodies are proteins ("immunoglobulins") which are transported around the body in the bloodstream as part of the plasma protein. What body system do lymphocytes originate from, and what other functions does that system perform? lymphatic system - lymph vessels and lymph nodes, spleen & thymus - closely related to the blood circulatory system also functions in processing of products of digestion of fats & oils (lipids) - connected to the lacteals inside villi in the small intestine (ileum) What name is given to the outside layer of viruses and what is it composed of, chemically? capsid - protein or envelope - protein, lipid, carbohydrate? What name is given to the outside layer of bacteria and what is it composed of, chemically?

cell wall - protein and carbohydrate At the molecular level, antibodies are known to be shaped like the letter Y, with a reactive site at the tip of each branch, so that antibodies can become attached to antigens on the basis of their molecular shape, rather like an enzyme and substrate. This can cause the infecting micro-organisms to stick together, and neutralises them until they are taken away and dealt with by other white cells. What name is given to the other white cells, and how do they deal with the infecting micro-organisms? phagocytes - engulf (ingest and digest) them! The production of antibodies can be used to explain - normal recovery from infection by bacteria or viruses - the primary immune response - immunity to a subsequent infection by the same organism - the secondary immune response - susceptibility to other micro-organisms (or different varieties or strains of the same micro-organism). Why is there a gap (in time) between first infection and recovery? It takes some time for the chain of events: recognition of invaders,cell division to make adequate numbers of the lymphocytes which produce the correct antibodies. How can antibodies explain immunity to subsequent infection?

Some white cells ("memory cells") remain after "beating" an infection and are able to divide rapidly to produce more lymphocytes which will produce the correct antibodies, so that the infection is quickly dealt with (or not even noticed). Why are we susceptible to other (i.e. different) infecting micro-organisms, after our body has "fought off" an infection? Because other micro-organisms have different antigens, and the immune system must start again from scratch. Why do common diseases like the cold, and flu, sometimes come back again year after year, often as epidemics? Different strains have different antigens on the outside, so the body's immune system may not be prepared for that specific strain, so that it can get into cells and reproduce. Why is there great concern about the emergence of antibiotic-resistant strains of more virulent disease such as tuberculosis? The body's immune system alone was not enough to prevent epidemics of these diseases, and treatment with antibiotics tipped the balance in our favour. If strains of these pathogens are selected due to improper use of antibiotics, there will be fewer medical alternatives. What is the difference (in biological terms) between immunity and resistance?

Immunity applies to a person or other organism who has an antibody-based protection against an infecting organism - bacterium or virus. Never say that a bacterium is immune to, or has immunity to, an antibiotic, for instance. Resistance applies to the ability of a micro-organism to survive the effects of an antibiotic. It is a property of the pathogenic micro-organism, not a weakness or chemical property of the antibiotic, and unrelated to the organism which is being infected - usually human or Man's stock animals. Since resistance to antibiotics is likely to be genetically based, there is fear that populations of resistant strains may become established. Never say that bacteria are spread, or grow - examiners prefer to be told that bacteria reproduce (asexually). The antigen-antibody reaction is also the basis for immunisation programs (vaccination), in which exposure to a related, weakened or dead form of a pathogenic organism, or even parts of its outer coat, brings about an immune response which is similar to the body's normal reaction to the more powerful or virulent form which would be difficult to fight off. Both of these - natural infection and exposure to vaccine - result in active immunity. Passive immunity is based on ready-made antibodies.

For example babies obtain these from their mother's bloodstream and first milk (colostrum) . Passive immunity may also be obtained via serum - derived from blood of organisms exposed to a pathogen. The specificity of this antigen-antibody reaction can be of even more use to Man when it is further refined and developed. The development of monoclonal antibodies The normal antigen-antibody reaction described above is often the result of several antibodies produced in response to several different antigens on the surface of an invading micro-organism. Since several different lymphocytes are involved in the production of a cocktail of antibodies, these are known as polyclonal antibodies. A method of using the specificity of action of single antibodies in the lab was recently discovered by Cesar Milstein and co-workers, who made it possible to produce pure antibodies to almost any substance, to order. However they had to overcome a problem that lymphocytes only survive inside a living body - they cannot be grown in the laboratory in the same way that some other cells can. In the laboratory, an animal, e.g. a mouse, is exposed to the foreign substance, which after a few days results in the production of a mixture of antibodies in response to the antigens responsible.

White cells are then extracted from the animal (actually from its spleen - an organ which regulates many of the functions of blood) and fused with cells taken from a cancerous tumour. A detergent (which lowers the surface tension) is used, together with gentle agitation. How will this assist in the fusion process? By chemically disrupting the cell membrane (which contains lipids) - and physically bringing cells close together, allowing cytoplasm of tumour cells and lymphocytes to join together Why is this fusion necessary? This has to be done because antibody-producing cells do not live long or divide in laboratory culture, whereas cancer cells grow rapidly (the reason they cause the tumour in the first place). The result is a collection of cells including hybrid (hybridoma) cells which must be separated into single cells and then given the opportunity to grow into groups. Why is it a collection of cells, and why must they be separated out? There will be some unfused lymphocytes, unfused tumour cells, and even some double fusions of the same type! There are also likely to be several different antibody-producing lymphocyte-tumour hybrids. Each group of cells is called a clone because it is derived from a single cell.

These are then tested to see if they are producing antibodies for the particular target substance. Since they are genetically identical, all the cells produce the same antibody, which builds up in the nutrient medium surrounding the cells. This is easily purified, resulting in a product containing molecules of a single antibody - not a mixture. Since the final result is due to the action of many cells derived originally from a single lymphocyte cell, these are called monoclonal antibodies. What is the name of the (nuclear) process that takes place as the (single) cells divide to make a clone? mitosis Potential applications of monoclonal antibodies Due the the specificity of their binding properties, monoclonal antibodies may have a wide variety of possible uses. Possibilities include the following: - Identification of odd substances produced by the body in special circumstances, e.g. hormones produced in pregnancy, or abnormal metabolites which enable screening for genetic abnormalities, drugs, etc and other health problems. What is the name of the hormone, produced in pregnancy, on which pregnancy testing is based? human chorionic gonadotrophin (hCG) - Identification and quantification of circulating micro-organisms, possibly in small numbers or too small to see under the microscope, e.g.

infecting viruses. - Industrial processing, either by concentrating products which are needed, or by removing unwanted substances. For example, blood products such as factor 8, which is needed by haemophiliacs, could be processed using monoclonal antibodies in such a way as to avoid viruses which may be present in only a small number of cases but which pose a major problem when blood products are produced from a pooled source. - To target and identify, neutralise or remove unwanted substances from the body, especially the blood plasma. Examples might include drugs taken in overdose. - If a particular type of cancer with cells widespread in the body can be shown to have different antigens than ordinary cells then it may be possible to treat cancer by targeting only the unwanted cells in the body. One way in which this could be done is by attaching poison to antibodies which will build up only in the cancer cells and killing them, whilst having more or less no effect on ordinary cells which have different antigens. The potent plant poison ricin has been investigated in this context. - Reducing the possibility of rejection in transplants by more accurate tissue typing between recipient and possible donors.

Antibody | definition of Antibody by Medical dictionary Antibody | definition of Antibody by Medical dictionary Related to Antibody: monoclonal antibody antibody [an´tĭ-bod″e] an immunoglobulin molecule having a specific amino acid sequence that gives each antibody the ability to adhere to and interact only with the antigen that induced its synthesis. This antigen-specific property of the antibody is the basis of the antigen-antibody reaction that is essential to an immune response . The antigen-antibody reaction begins as soon as substances interpreted as foreign invaders gain entrance into the body. See also immunity . Abbreviated Ab. Antibodies are synthesized by the plasma cells formed when antigen-specific groups ( clones ) of B lymphocytes respond to the presence of antigen. The developmental process of antibody production begins when stem cells are transformed into B lymphocytes; this transformation usually is completed a few months after birth, at which time the lymphocytes migrate to lymphoid tissue primarily located in the lymph nodes, although they are also found in the spleen, gastrointestinal tract, and bone marrow.

Antibody production, its interaction with a specific antigen, and the activation of complement (C), an interrelated group of eleven proteins, are the major components of the humoral system of immunity. Antibody-mediated immunity. From Applegate, 2000. Fortunately, the immune response of antibody and complement can be transferred passively from one individual to another, as for example the transfer of maternal antibody across the placental barrier to the fetus, who has not yet developed a mature immune system. An antibody present in an individual without known prior exposure to the corresponding red cell antigen is termed an isoagglutinin . (Examples are the ABO antibodies anti-A, anti-B, and anti-A,B.) Antibodies can be classified according to their mode of action as they react to and set about defending the body against foreign invaders. Some cause clumping together of bacterial cells ( agglutination ) and are called agglutinins . Those antibodies that cause bacterial cells to dissolve or liquefy are called bacteriolysins . This activity is assisted by complement , which interacts with the antigen-antibody complex in such a way that the cell ruptures and there is dissolution ( lysis ) of the cell body.

Opsonins coat the outside of bacteria, making them more attractive to phagocytes. Other types of antibodies include those that neutralize the toxins of antigens ( antitoxins ) and those that cause precipitation of antigens in a fluid medium ( precipitins ). anaphylactic antibody a substance formed as a result of the first injection of a foreign anaphylactogen and responsible for the anaphylactic symptoms following the second injection of the same anaphylactogen. antinuclear a's (ANA) autoantibodies directed against components of the cell nucleus, e.g., DNA, RNA, and histones; they may be detected by immunofluorescence. A positive ANA test is characteristic of systemic lupus erythematosus. Antinuclear antibodies also occur in patients with rheumatoid arthritis, Sjögren's syndrome, and scleroderma. blocking antibody any antibody that by combining with an antigen blocks another immunologic reaction with the antigen.

Immunotherapy (hypersensitization) for allergic disorders induces in most treated patients IgG blocking antibodies that can bind the allergen and prevent it from binding to cell-fixed IgE and trigger immediate hypersensitivity; thus it can induce partial immunologic tolerance. Blocking antibodies can prevent agglutination in serologic tests. complement-fixing antibody antibody (primarily IgM and the IgG subclasses 1, 2, and 3) that activates complement when reacted with antigen. complete antibody antibody capable of agglutinating cells in physiologic saline solution. cross-reacting antibody one that combines with an antigen other than the one that induced its production. cytophilic antibody cytotropic antibody . cytotoxic antibody any specific antibody directed against cellular antigens, which when bound to the antigen, activates the complement pathway or activates killer cells, resulting in cell lysis. cytotropic antibody any of a class of antibodies that attach to tissue cells (such as mast cells and basophils) through their Fc segments to induce the release of histamine and other vasoconstrictive amines important in immediate hypersensitivity reactions.

In humans this antibody, also known as reagin , is of the immunoglobulin class known as IgE. Called also cytophilic antibody . heterophil antibody a characteristic antibody found with many cases of infectious mononucleosis; see also heterophil antibody . immune antibody a type of isoantibody induced by immunization, either by pregnancy or by transfusion, in contrast to natural antibodies. incomplete antibody 1. antibody that binds to erythrocytes or bacteria but does not produce agglutination; in blood banking, the nonagglutinating antibody is detectable in serum by using the antiglobulin (Coombs') test. For example, IgG anti-Rh antibodies do not agglutinate erythrocytes in physiologic saline whereas IgM antibodies do. 2. a univalent antibody fragment.

monoclonal a's (MOAB) proteins produced from a single clone of B lymphocytes ; used as laboratory reagents in radioimmunoassays, ELISA assay, and immunofluorescence assays, and also as biological response modifiers fused with rapidly reproducing myeloma cells, resulting in a hybridoma capable of synthesizing a massive amount of one specific antibody; the antibody is made in response to tumor cells injected into mice and is produced from mouse serum. Monoclonal antibodies may be used alone (unconjugated) or bound (conjugated) to radioisotopes, toxins, or other biological response modifiers . When bound to radioisotopes they may also be used as a diagnostic tool to locate tumors and metastatic disease. natural a's (naturally occurring a's) antibodies present in the serum of normal individuals in the apparent absence of any contact with the specific antigen, probably induced by exposure to cross-reacting antigens; examples are the ABO antibodies, anti-A and anti-B. Such antibodies may play a major role in resistance to infection. neutralizing antibody one that reduces or destroys infectivity of a homologous infectious agent by partial or complete destruction of the agent.

protective antibody one responsible for immunity to an infectious agent, observed in passive immunity. Rh a's those directed against Rh antigen(s) of human erythrocytes. Not normally present, they may be produced when Rh-negative persons receive Rh-positive blood by transfusion or when an Rh-negative person is pregnant with an Rh-positive fetus. saline antibody complete antibody . an·ti·bod·y (Ab), (an'tē-bod'ē), Avoid the jargonistic use of the plural antibodies when the reference is to a single antibody species. An immunoglobulin molecule produced by B-lymphoid cells that combine specifically with an immunogen or antigen. Antibodies may be present naturally, their specificity is determined through gene rearrangement or somatic replacement or may be synthesized in response to stimulus provided by the introduction of an antigen; antibodies are found in the blood and body fluids, although the basic structure of the molecule consists of two light and two heavy chains, antibodies may also be found as dimers, trimers, or pentamers. After binding antigen, some antibodies may fix, complement, bind to surface receptors on immune cells, and in some cases may neutralize microorganisms.

Synonym(s): immune protein , protective protein , sensitizer (2) antibody /an·ti·body/ (Ab) (an´tĭ-bod-e) an immunoglobulin molecule that reacts with a specific antigen that induced its synthesis and with similar molecules; classified according to mode of action as agglutinin, bacteriolysin, hemolysin, opsonin, or precipitin. Antibodies are synthesized by B lymphocytes that have been activated by the binding of an antigen to a cell-surface receptor. See immunoglobulin . anaphylactic antibody IgE antibody causing anaphylaxis. antimitochondrial antibodies circulating antibodies directed against inner mitochondrial antigens seen in almost all patients with primary biliary cirrhosis. antinuclear antibodies (ANA) autoantibodies directed against components of the cell nucleus, e.g., DNA, RNA, and histones. antireceptor antibodies autoantibodies against cell-surface receptors, e.g., those directed against β2-adrenergic receptors in some patients with allergic disorders.

antisperm antibody (ASA) any of various surface-bound antibodies found on sperm after infection, trauma to the testes, or vasectomy ; they interfere with the fertilization process or result in nonviable zygotes . antithyroglobulin antibodies those directed against thyroglobulin, demonstrable in about one-third of patients with thyroiditis, Graves' disease, and thyroid carcinoma. blocking antibody 1. one (usually IgG) that reacts preferentially with an antigen, preventing it from reacting with a cytotropic antibody (IgE), and producing a hypersensitivity reaction. (ăn′tĭ-bŏd′ē) n. pl. antibod·ies A Y-shaped protein on the surface of B cells that is secreted into the blood or lymph in response to an antigenic stimulus, such as a bacterium, virus, parasite, or transplanted organ, and that neutralizes the antigen by binding specifically to it; an immunoglobulin. antibody (Ab) [an′tibod′ē] Etymology: Gk, anti + AS, bodig an immunoglobulin produced by B-lymphocytes in response to bacteria, viruses, or other antigenic substances.

An antibody is specific to an antigen. Each class of antibody is named for its action. Antibodies include agglutinins, bacteriolysins , opsonins , and precipitins. See also antiantibody , B cell , immune response . antibody An immunoglobulin produced by plasma cells, which has a specific amino acid sequence and specifically binds to the antigen(s) (e.g., foreign proteins, microbes or toxins) that induced its synthesis; antibodies may also bind to closely related antigens. antibody Immunology An immunoglobulin produced by plasma cells, which has a specific amino acid sequence and specifically binds to the antigen(s)–eg, foreign proteins, microbes or toxins, that induced its synthesis; antibodies may bind to closely related antigens.

See Acetylcholine receptor antibody , Anticardiolipin antibody , Anticentromere antibody, Anti-double-stranded DNA antibody, Anti-epidermal antibody, Anti-extractable nuclear antibody, Antigliadin antibody , Antihistone antibody, Anti-idiotype antibody, Anti-insulin antibody , Anti-islet cell antibody , Anti-Jo-1 antibody, Anti-LANA antibody, Antimicrosomal antibody, Antimitochondrial antibody, Antimyelin antibody , Antimyeloperoxidase antibody, Antineuronal-nuclear antibody, Antineutrophil cytoplasmic antibody , Antinuclear antibody , Antiparietal cell antibody , Anti-platelet antibody, Anti-PRP antibody, Anti-Purkinje cell antibody, Anti-receptor antibody , Anti-reticulin antibody, Anti-ribosomal antibody, Anti-Ro/SSA antibody, Anti-single-stranded DNA antibody, Anti-striated muscle antibody, Anti-thyroglobulin antibody , Antithyroid antibody , Antithyroid peroxidase antibody , Anti-tumor necrosis factor- α monoclonal antibody, Autoantibody , Bexxar radiolabeled monoclonal antibody,

 Secondary antibody, Binding antibody, Blocking antibody, Catabolic antibody, Catalytic antibody, Chimeric antibody, Core antibody , Cross-reactive antibody, Designer antibody, Enhancing antibody, Fluorescent treponemal antibody, Functional antibody, GAD antibody, Glutamic acid decarboxylase autoantibody, HAMA antibody, Heterophile antibody, HIV antibody , HTLA antibody, Humanized antibody , Immunoglobulin , Insulin receptor antibody , Intrinsic factor antibody, Islet antibody , Isotypic control antibody, Ku antibody, LW antibody, Miniantibody , MOC-31 antibody, Monoclonal antibody , Neutralizing antibody, Parietal cell antibody, Plantibody antibody, PM-1 antibody, Polyclonal antibody, Primary antibody, Purkinje cell antibody, RANA antibody, Scleroderma antibody, Sjögren antibody, Sm antibody, Smooth muscle antibody , Sperm antibody, Thyroid stimulating hormone receptor antibody, Trichinosis antibody, Warm antibody .

an·ti·bod·y (Ab) (an'ti-bod-ē) An immunoglobulin molecule with a specific amino acid sequence evoked in humans or other animals by an antigen and characterized by reacting specifically with the antigen in some demonstrable way, produced by B lymphocytes in response to an antigen. It is believed that antibodies also may exist naturally, without being present as a result of the stimulus provided by the introduction of an antigen. acetylcholine receptor binding antibody Abbreviation: AChR-Ab An autoantibody against acetylcholine receptors in the neuromuscular junction. Binding, blocking, or modulating antibodies against this receptor are found in the blood of most patients with generalized myasthenia gravis and in about half of all patients with ocular forms of the disease. illustration agonistic antibody An antibody that stimulates or activates an organ. E.g., agonistic antibodies against the thyrotropin receptor in Grave disease stimulate the thyroid gland to release thyroid hormones that produce hyperthyroidism. anticardiolipin antibody Abbreviation: aCLa An autoantibody against the cell membrane lipid, diphosphatidyl glycerol.

It produces abnormal and sometimes life-threatening blood clotting. The antibody is found in a variety of autoimmune and infectious diseases, including in patients with the antiphospholipid antibody syndrome and syphilis. anticyclic citrullinated peptide antibody Abbreviation: anti-CCP An antibody found in the serum of patients with rheumatoid arthritis but not in those with other joint or soft tissue diseases. anti–DNase B antibody An antibody formed during infection with group A beta-hemolytic streptococci. It is used, retrospectively, to help diagnose recent streptococcal infections. antiendomysial antibody An antibody that cross-reacts with smooth muscle collagen and the gluten in wheat, found in the serum of people with celiac sprue and some related autoimmune diseases. antiendothelial cell antibody An autoantibody present in the serum of patients with a variety of autoimmune diseases, including scleroderma (systemic sclerosis), systemic lupus erythematosus, interstitial lung diseases, and sarcoidosis. They attach to antigens on the cells that line blood vessels and injure those cells, producing blood vessel injury and inflammation (vasculitis).

antifibrillarin antibody An autoantibody to the nucleolar protein fibrillarin, found in patients with diffuse systemic sclerosis (scleroderma), esp. those with relatively severe disease. It is identified more often in men than in women with the disease and in people of African descent as opposed to Europeans or Asians. antiganglioside antibody An antibody formed against the chemical components of nerves, found in the serum of those with Guillain-Barré syndrome. antigliadin antibody An antibody formed against the gluten in wheat, found in the serum of people with celiac sprue. antileukocyte antibody Any antibody found in plasma that, when donated and infused into a recipient, damages the recipient's white blood cells. Leukocyte injury after plasma exchange or infusion is the event that triggers transfusion-related acute lung injury. anti-Hu antibody An antibody found in patients with several autoimmune vasculitides, such as microscopic polyangitis. Synonym: perinuclear anti–neutrophil cytoplasmic antibody antineuronal nuclear antibody Abbreviation: ANNA Any of several antibodies that bind to neuronal targets in the cerebrum and cerebellum, producing paraneoplastic neurological dysfunction.

The antibodies are typically released by cancers such as small-cell carcinoma of the lung (also known as ANNA-1 and ANNA-2), testicular cancer (anti-Ta antibody), or breast cancer (ANNA-2). antineutrophil cytoplasmic antibody Abbreviation: ANCA An autoantibody found in the blood of patients with certain forms of vasculitis (such as Churg-Strauss syndrome, microscopic polyangiitis, Wegener granulomatosis) esp. when it affects small blood vessels. antinuclear antibody Abbreviation: ANA Any of a group of autoantibodies that react against normal components of the cell nucleus. These antibodies are present in a variety of immunologic diseases, including systemic lupus erythematosus, progressive systemic sclerosis, Sjögren syndrome, scleroderma, polymyositis, and dermatomyositis, and in some patients taking hydralazine, procainamide, or isoniazid. In addition, ANA is present in some normal people. Tests for ANAs are used in the diagnosis and management of autoimmune diseases.

antiphospholipid antibody Abbreviation: aPLa Any of a group of immunoglobulin autoantibodies that react with phospholipids, which are one of the primary components of the cell membrane (the other components are glycolipids and steroids). These antibodies are found in patients with a variety of connective tissue and infectious disorders, including systemic lupus erythematosus, the antiphospholipid antibody syndrome, syphilis, and malaria. They cause abnormal blood clotting, thrombocytopenia; and in women of childbearing age, repeated miscarriages. The anticardiolipin antibodies are one type of antiphospholipid antibody. anti–proliferating cell nuclear antigen (PCNA) antibody Abbreviation: anti-PCNA An antibody found in the blood of patients with diseases in which cells replicate rapidly. Such conditions include autoimmune and inflammatory diseases and malignancies. antiproteinase-3 antibody An autoantibody found in patients with small blood vessel vasculitides, such as Wegener granulomatosis.

Synonym: diffusely cytoplasmic anti–neutrophil antibody antireceptor antibody An antibody that reacts with the antigen receptor on a cell rather than with an antigen itself. antiribosomal P antibody An autoantibody found in patients with systemic lupus erythematosus, esp. those with neurological or psychiatric manifestations of the disorder. anti-scl-70 antibody An antibody produced by the mother and transferred to the fetus in utero or during breastfeeding. monoclonal antibody Abbreviation: MoAB A type of antibody, specific to a certain antigen, created in the laboratory from hybridoma cells. Because monoclonal antibodies are derived from a single cell line and raised against a single antigen, they are highly specific. Diagnostically, they are used to identify microorganisms, white blood cells, hormones, and tumor antigens. In patient care, they are used to treat transplant rejection, certain cancers, and autoimmune diseases. Hybridoma cells, used to produce monoclonal antibodies, are formed by the fusion of a spleen cell from a mouse immunized with an antigen and a multiple myeloma cell (a cancerous plasma B cell).

The fused cells are screened to identify those that secrete antibodies against a specific antigen. A continuous supply of these antigen-specific monoclonal antibody secreting cells can then be grown in cultures. See: antibody; B cell ; hybridoma natural antibody An antibody present in a person without known exposure to the specific antigen, such as an anti-A antibody in a person with B blood type. panel reactive antibody Abbreviation: PRA A measure of an organ transplant recipient's level of sensitization to antigens on donated organs. It is the percentage of cells taken from a broad selection of blood donors against whose antigens the organ recipient's serum reacts. The higher the panel reactive antibody, the more challenging it is to match a donor organ to the recipient. perinuclear antineutrophil cytoplasmic antibody Warm autoagglutinin. illustration antibody A Y-shaped protein molecule, called an IMMUNOGLOBULIN , produced by the B group of lymphocytes in response to the presence of a ANTIGEN . An appropriate B lymphocyte is selected from the existing repertoire. This then produces a clone of PLASMA CELLS each capable of synthesizing large numbers of specific antibodies to combat the infection. The B cells also produce memory cells.

Subsequent infection with the same antigen prompts the memory cells to clone plasma cells and produce the correct antibodies without further delay. This is an important way in which an infection leads to subsequent immunity. Antibodies are able to neutralize antigens or render them susceptible to destruction by PHAGOCYTES in the body. The basic structure of an antibody consists of four polypeptide chains linked by disulphide bridges, two larger structures called HEAVY CHAINS and two smaller called LIGHT CHAINS . antibody (Ab) a type of protein called an IMMUNOGLOBULIN that reacts with a specific ANTIGEN , and serves as part of a vital body-defence mechanism. Various reactions can occur between antigen and antibody. If the antigen is a TOXIN (as in snake venom, or as produced by bacteria causing, for example, botulism and tetanus), neutralizing antibodies are called antitoxins. If the antigen is adhering to the surface of a cell, antibodies called agglutinins cause clumping or AGGLUTINATION of cells, while another antibody type (lysins) cause disintegration or LYSIS of the cell in conjunction with COMPLEMENT .

Other antibodies (opsonins) facilitate uptake of antigens by PHAGOCYTES in the blood, while precipitins cause soluble antigens to precipitate. Antibodies are produced in the lymphoid tissues of the body, e.g. LYMPH NODES , by a type of LYMPHOCYTE called B-CELLS . Most antibodies are produced during exposure to an antigen, such a response being termed active immunity. Specific antibodies to rare or synthetic antigens can be manufactured as easily as those to common antigens. A few antibodies are produced even without the apparent presence of the appropriate antigen. Such ‘natural’ antibodies include several involved in blood grouping, e.g. A and B antibodies in the ABO BLOOD GROUP . Young mammals have limited capacity to produce antibodies in the first few weeks of life, but can obtain some passive immunity by receiving maternal antibodies via the mother's milk. This fact has been used to encourage human mothers to breast-feed their infants rather than bottle-feed. Most antibodies circulate in the blood and other body fluids, but most if not all body secretions also contain antibodies, mainly of the IgA type; See IMMUNOGLOBULIN .

Antibody A protein manufactured by a type of white blood cells called lymphocytes, in response to the presence of an antigen, or foreign protein, in the body. Because bacteria, viruses, and other organisms commonly contain many antigens, antibodies are formed against these foreign proteins to neutralize or destroy the invaders.

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naires' Disease , Maternal to Fetal Infections , Multiple Myeloma , Myasthenia Gravis , Noroviruses , Plasmapheresis , Polyglandular Deficiency Syndromes , Prostate-Specific Antigen Test , Rabies , Radiation Therapy , Respiratory Syncytial Virus Infection , Rubella Test , Serum Sickness , Shingles , Streptococcal Antibody Tests , Stress Reduction , Threadworm Infection , Tissue Typing , TORCH Test , Transfusion , Tuberculin Skin Test , Typhus , Vaginal Pain , Vasculitis , Waldenström's Macroglobulinemia , X-Linked Agammaglobulinemia immunoglobulin ; Ig; antibody structurally related proteins (two pairs of polypeptide chains linked by disulphide bond, as one pair of light (L) and one pair of heavy (H) chains, classified (as immunoglobulin (Ig) G, IgA, IgM, IgD and IgE) by heavy-chain structure and antigenic properties antibody, n any of a wide assortment of glycoproteins typically present in the bloodstream that attack antigens during an immune response.

antibody Any of a large variety of proteins normally present in the body or produced in response to an antigen, which it is capable of combining with and destroying, thus producing an immune reaction. Antibodies are produced by a type of white blood cell called B cell (B lymphocyte) secreted by lymphatic tissue (e.g. bone marrow, lymph nodes) usually in response to an antigen. Some eye diseases are antibody-dependent (e.g. allergic conjunctivitis, atopic keratoconjunctivitis, vernal conjunctivitis). an·ti·bod·y (Ab) (an'ti-bod-ē) Avoid the jargonistic use of the plural antibodies when the reference is to a single antibody species. An immunoglobulin molecule produced by B-lymphoid cells that combine specifically with an immunogen or antigen. Antibodies may be present naturally; their specificity is determined through gene rearrangement or somatic replacement or may be synthesized in response to stimulus provided by the introduction of an antigen. antibody (an´tibodē), n 1.

a specific substance that is produced by an animal as a reaction to the presence of an antigen and that reacts specifically with an antigen in some observable way. n 2. an immunoglobulin (preferred term), essential to the immune system, produced by lymphoid tissue in response to bacteria, viruses, or other antigenic substances. Each type is identified by its action, agglutinins, bacteriolysins, opsonins, and precipitins. See also immunoglobulins. antibody, antinuclear, What Are White Blood Cells? - Health Encyclopedia - University of Rochester Medical Center URMC / Encyclopedia / Content What Are White Blood Cells? White blood cells are an important component of your blood system, which is also made up of red blood cells, platelets, and plasma. Click to Enlarge Although your white blood cells account for only about 1% of your blood, their impact is significant. White blood cells, also called leukocytes, are essential for good health and protection against illness and disease. Think of white blood cells as your immunity cells. In a sense, they are continually at war. They flow through your bloodstream to battle viruses, bacteria, and other foreign invaders that threaten your health.

When your body is in distress and a particular area is under attack, white blood cells rush in to help destroy the harmful substance and prevent illness. White blood cells are made inside the bone marrow and stored in your blood and lymphatic tissues. Because some white blood cells have a short lifespan of one to three days, your bone marrow is constantly making them. Click to Enlarge Types of white blood cells Among your white blood cells are: Monocytes. They have a longer lifespan than many white blood cells and help to break down bacteria. Lymphocytes. They create antibodies to defend against bacteria, viruses, and other potentially harmful invaders. Neutrophils. They kill and digest bacteria and fungi. They are the most numerous type of white blood cell and your first line of defense when infection strikes. Basophils. These small cells appear to sound an alarm when infectious agents invade your blood. They secrete chemicals such as histamine, a marker of allergic disease, that help control the body's immune response. Eosinophils. They attack and kill parasites, destroy cancer cells, and help with allergic responses.

Problems affecting white blood cells Your white blood cell count can be low for a number of reasons—when something is destroying the cells more quickly than the body can replenish them or when the bone marrow stops making enough white blood cells to keep you healthy. When your white blood cell count is low, you are extremely susceptible to any illness or infection, which can spiral into a serious health threat. Your healthcare provider can see whether your white blood cell count is normal through a blood test known as the complete blood count. If your count is too low or too high, you may have a white blood cell disorder. A number of diseases and conditions may influence white blood cell levels: Weakened immune system. This is often caused by illnesses such as HIV/AIDS or by treatments related to cancer. Cancer treatments such as chemotherapy or radiation therapy can destroy white blood cells and leave you vulnerable to infection. Infection. A higher-than-normal white blood cell count usually indicates some type of infection—white blood cells are multiplying to destroy an enemy, such as bacteria or a virus. Myelodysplastic syndrome. This condition causes abnormal production of blood cells. This includes white blood cells in the bone marrow. Cancer of the blood.

Cancers including leukemia and lymphoma can cause uncontrolled growth of an abnormal type of blood cell in the bone marrow. This results in a greatly increased risk for infection and or serious bleeding. Myeloproliferative disorder. This disorder refers to various conditions that trigger the excessive production of immature blood cells. This can result in an unhealthy balance of all types of blood cells in the bone marrow and too many or too few white blood cells in the blood. Medicines. Some medicines can raise or lower the body's white blood cell count. Other conditions, such as extreme physical stress caused by an injury or emotional stress, can trigger high white blood cell levels. So can inflammation, labor or the end of pregnancy, smoking, or even extreme exercise. Medical Reviewers:

Question: What substance is produced by white blood cells in response to the action of a foreign body?
Answer: Antibody