Sarah Bennett
Antibodies are protective proteins produced by the immune system to fight off harmful invaders and abnormal cells. They are produced by B cells, a type of white blood cell called lymphocytes, which work with other cells in the immune system to combat antigens. Antigens are foreign substances that enter the body, such as bacteria, fungi, viruses, and toxins, and they stimulate the production of antibodies. This process involves antigen-presenting cells (APC) attaching to the antigen and breaking it down, after which helper T cells are activated and spur B cells into action. This results in the production and secretion of antibodies, which attach to specific antigens to neutralize or eliminate them from the body.
| Characteristics | Values |
|---|---|
| Substances that stimulate the production of antibodies | Antigens, including toxins, bacteria, foreign blood cells, and the cells of transplanted organs |
| Cells that produce antibodies | B cells, specifically B lymphocytes |
| Antibody characteristics | Y-shaped molecules with two identical antigen-binding sites; each antibody has a unique antigen-binding site |
| Antibody types | Monoclonal antibodies, which are created in a lab, and natural antibodies |
| Antibody functions | Protective proteins that attach to antigens (foreign substances) and remove them from the body |
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What You'll Learn
B cells
When the immune system detects antigens—markers that indicate the presence of harmful substances—B cells produce antibodies to fight the invader. Each B cell produces a single species of antibody, each with a unique antigen-binding site.
The first class of antibody made by a developing B cell is IgM, which has μ heavy chains. IgM is also the major class of antibody secreted into the blood during the early stages of a primary antibody response, upon first exposure to an antigen.
Once activated by an antigen, naïve or memory B cells proliferate and differentiate into antibody-secreting effector cells. These effector cells produce antibodies with the same unique antigen-binding sites as the cell-surface antibody that served as the antigen receptor.
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Antigens
There are several types of antigens, including exogenous, endogenous, autoantigens, and tumour antigens. Exogenous antigens come from foreign substances that enter the body through the nose, mouth, or cuts in the skin. Endogenous antigens exist on cells inside the body and signal whether they are friendly ("self") or harmful ("non-self"). Autoantigens are markers on cells that the immune system attacks even though they are not harmful, leading to autoimmune diseases. Tumour antigens are found on cancer cells.
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Antibody tests
Antibodies are proteins produced by the body's immune system to fight foreign substances such as bacteria and viruses. B cells, a type of white blood cell, produce antibodies in response to antigens (foreign substances).
ANA (Antinuclear Antibody) Test
This test checks for antinuclear antibodies in the blood. While it is normal to have a few antinuclear antibodies, a large number may indicate an autoimmune disorder, where the body attacks its own healthy cells. A positive result may also be due to a viral infection or other health conditions such as cancer. However, a negative result does not completely rule out the possibility of an autoimmune disorder.
Epstein-Barr Virus (EBV) Antibody Test
The Epstein-Barr Virus (EBV) is a common cause of infectious mononucleosis (mono). Antibody tests for EBV are used to help diagnose EBV infection, especially in individuals with symptoms of mono but a negative mono test. These tests can distinguish between a current, recent, or past EBV infection and can be important for pregnant women with flu-like symptoms to determine the cause.
COVID-19 Antibody Test
The COVID-19 antibody test detects antibodies to SARS-CoV-2 in individuals who have been exposed to the virus or received a vaccine. It is recommended to wait at least three weeks after symptom onset or exposure before taking the test, as it can take time for the body to develop detectable levels of antibodies. False negative results can occur if the test is taken too soon, and false positive results may occur due to cross-reactivity with other coronaviruses.
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Passive immunity
Maternal passive immunity, or natural passive immunity, is transferred from a mother to her child. Antibodies pass across the placenta to the unborn child, providing protection against infections in the first few months of life. After birth, the infant continues to receive passive immunity from antibodies in breast milk, especially colostrum, the protein-rich milk produced in the first few days after birth. Maternal passive immunity is crucial for safeguarding infants until their immune system matures.
Artificial passive immunity, on the other hand, is achieved by injecting antibodies generated by another person, animal, or artificial process into an individual. These antibody-containing preparations are known as antisera and are used therapeutically when there is a risk of infection. Passive immunity through antibody-containing blood products, such as immune globulin, can be administered when immediate protection against a specific disease is necessary.
The main advantage of passive immunity is that it provides immediate protection. However, it is generally short-lived, as the supply of antibodies is not continuously replenished as it would be in an individual generating them through their immune system.
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Monoclonal antibodies
The generation of mAbs for use in humans was established in 1975 by Georges Köhler and César Milstein, who fused myeloma cell lines with B cells to create hybridomas. These hybridomas could produce antibodies specific to known antigens and were immortal. In 1988, Gregory Winter and his team pioneered techniques to humanize monoclonal antibodies, reducing the adverse reactions some patients experienced.
There are four different types of monoclonal antibodies, classified based on their composition: murine, chimeric, humanized, and human. Murine monoclonal antibodies are made from mouse proteins, while chimeric monoclonal antibodies are a combination of mouse and human proteins. Humanized monoclonal antibodies are made from small parts of mouse proteins attached to human proteins, and human monoclonal antibodies are composed of fully human proteins.
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Frequently asked questions
Antigens are the substances that stimulate the production of antibodies. Antigens include toxins, bacteria, foreign blood cells, and the cells of transplanted organs.
Antibodies are protective proteins produced by the immune system. They attach to antigens (foreign substances) and remove them from the body.
Antigens are foreign substances that enter the body. They are markers that allow the immune system to identify harmful substances.
Each antibody has a unique antigen-binding site that attaches to a specific antigen. This makes it easier for immune cells to identify and destroy the antigen.
