- Also called:
- immunoglobulin
- Related Topics:
- immune antibody
- IgM
- IgG
- IgE
- IgD
antibody
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What is an antibody?
An antibody, also known as an immunoglobulin, is a protective protein produced by the immune system in response to a foreign substance called an antigen. Antibodies recognize and latch onto antigens to remove them from the body.
When an alien substance enters the body, the immune system recognizes it as foreign because molecules on the surface of the antigen differ from those found in the body. Antibodies are produced by specialized white blood cells called B lymphocytes, or B cells. Once begun, antibody production continues for several days until all antigen molecules are removed, and they remain in circulation for several months, providing extended immunity against that particular antigen.
Each antibody molecule is essentially identical to the antigen receptor of the B cell that produced it.
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How do antibodies help protect the body?
When a foreign substance enters the body, the immune system recognizes it as foreign because molecules on the surface of the antigen differ from those found in the body. To eliminate the invader, the immune system uses antibody production, which is one of its most important mechanisms.
Antibodies are produced by specialized white blood cells called B lymphocytes (or B cells). When an antigen binds to the B-cell surface, it stimulates the B cell to divide and mature into a group of identical cells called a clone. The mature B cells, called plasma cells, secrete millions of antibodies into the bloodstream and lymphatic system.
As antibodies circulate, they attack and neutralize antigens that are identical to the one that triggered the immune response. Antibodies attack antigens by binding to them. The complement reaction can trigger the lysis (bursting) of the invading microbe or attract microbe-killing scavenger cells that ingest the invader.
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What are antigens, and how do antibodies recognize them?
Antigens are substances that trigger an immune response by activating lymphocytes, the body's white blood cells that fight infection. Foreign antigens come from outside the body, such as viruses or bacteria, while autoantigens originate within the body.
Antibodies recognize a portion of the antigenās surface known as the antigenic determinant, or epitope. Recognition occurs if the structures of the B cellās antigen receptor and the epitope are complementary, fitting together like puzzle pieces, which then activates the B-cell to produce antibodies. Each antibody molecule has two identical antigen-binding sites at the tips of its arms that bind to the antigen.
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What are the main parts or structure of an antibody?
An antibody molecule has a Y shape and consists of two identical heavy chains and two identical light chains. Each chain contains constant (C) and variable (V) regions.
The stem of the Y consists of one end of each of the two heavy chains, while each arm consists of the remaining portion of the heavy chain plus a light chain. At the tip of each arm is an antigen-binding site, which allows the antibody to recognize a specific part of the antigen.
Antibodies are grouped into five classes: IgG, IgM, IgA, IgD, and IgE.
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How are different types of antibodies (like IgA, IgG) used in the immune system?
Antibodies, also known as immunoglobulins (Ig), are produced by B-cells and are essential to the immune system. There are five classes: IgG, IgM, IgA, IgD, and IgE.
- IgG is the most common antibody, found in blood and tissue fluids, and is involved in general humoral immunity.
- IgM, with its five protein units, is very efficient at precipitating antigens so they can be removed by phagocytes.
- IgA is mainly in mucous membranes, like those lining the respiratory and gastrointestinal tracts, as well as in body secretions such as tears, saliva, and colostrum.
- IgD's function is not known.
- IgE takes part in immediate hypersensitivity reactions.
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How are antibodies used in medicine or scientific research?
Antibodies have key applications in both medicine and research. For instance, preformed antibodies from the blood serum of previously infected organisms can provide immediate, passive immunization against fast-acting toxins or microbes. Vaccines stimulate the immune system to produce antibodies, conferring active immunity.
Monoclonal antibodies, produced artificially, can recognize individual antigenic sites on molecules. Their specificity has enabled the creation of sensitive assays for biologically important substances and the identification of previously unknown marker molecules on cell surfaces, such as cancer antigens in tissue samples.
Monoclonal antibodies can also deliver cytotoxic drugs or radiation to cancer cells. Therapies like ipilimumab and nivolumab augment the immune response to facilitate tumor destruction.
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News •
antibody, a protective protein produced by the immune system in response to the presence of a foreign substance, called an antigen. Antibodies recognize and latch onto antigens in order to remove them from the body. A wide range of substances are regarded by the body as antigens, including disease-causing organisms and toxic materials such as insect venom.
How antibodies work
When an alien substance enters the body, the immune system is able to recognize it as foreign because molecules on the surface of the antigen differ from those found in the body. To eliminate the invader, the immune system calls on a number of mechanisms, including one of the most importantāantibody production. Antibodies are produced by specialized white blood cells called B lymphocytes (or B cells). When an antigen binds to the B-cell surface, it stimulates the B cell to divide and mature into a group of identical cells called a clone. The mature B cells, called plasma cells, secrete millions of antibodies into the bloodstream and lymphatic system.
As antibodies circulate, they attack and neutralize antigens that are identical to the one that triggered the immune response. Antibodies attack antigens by binding to them. The binding of an antibody to a toxin, for example, can neutralize the poison simply by changing its chemical composition; such antibodies are called antitoxins. By attaching themselves to some invading microbes, other antibodies can render such microorganisms immobile or prevent them from penetrating body cells. In other cases the antibody-coated antigen is subject to a chemical chain reaction with complement, which is a series of proteins found in the blood. The complement reaction either can trigger the lysis (bursting) of the invading microbe or can attract microbe-killing scavenger cells that ingest, or phagocytose, the invader. Once begun, antibody production continues for several days until all antigen molecules are removed. Antibodies remain in circulation for several months, providing extended immunity against that particular antigen.
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Antibodies and B cells
B cells and antibodies together provide one of the most important functions of immunity, which is to recognize an invading antigen and to produce a tremendous number of protective proteins that scour the body to remove all traces of that antigen. Collectively B cells recognize an almost limitless number of antigens; however, individually each B cell can bind to only one type of antigen. B cells distinguish antigens through proteins, called antigen receptors, found on their surfaces. An antigen receptor is basically an antibody protein that is not secreted but is anchored to the B-cell membrane.
All antigen receptors found on a particular B cell are identical, but receptors located on other B cells differ. Although their general structure is similar, the variation lies in the area that interacts with the antigenāthe antigen-binding, or antibody-combining, site. This structural variation among antigen-binding sites allows different B cells to recognize different antigens. The antigen receptor does not actually recognize the entire antigen; instead it binds to only a portion of the antigenās surface, an area called the antigenic determinant or epitope. Binding between the receptor and epitope occurs only if their structures are complementary. If they are, epitope and receptor fit together like two pieces of a puzzle, an event that is necessary to activate B-cell production of antibodies.
