Antibody and antigen

Antibody And Antigen 2819
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Antibodies, also called immunoglobulins, are proteins manufactured by the body that help fight against foreign substances called antigens. When an antigen enters the body, it stimulates the immune system to produce antibodies. (The immune system is the body's natural defense system.) The antibodies attach, or bind, themselves to the antigen and inactivate it.

Every healthy adult's body has small amounts of thousands of different antibodies. Each one is highly specialized to recognize just one kind of foreign substance. Antibody molecules are typically Y-shaped, with a binding site on each arm of the Y. The binding sites of each antibody, in turn, have a specific shape. Only antigens that match this shape will fit into them. The role of antibodies is to bind with antigens and inactivate them so that other bodily processes can take over, destroy, and remove the foreign substances from the body.

Antigens are any substance that stimulates the immune system to produce antibodies. Antigens can be bacteria, viruses, or fungi that cause infection and disease. They can also be substances, called allergens, that bring on an allergic reaction. Common allergens include dust, pollen, animal dander, bee stings, or certain foods. Blood transfusions containing antigens incompatible with those in the body's own blood will stimulate the production of antibodies, which can cause serious, potentially life-threatening reactions.

Classes of antibodies and their functions

There are five classes of antibodies, each having a different function. They are IgG, IgA, IgM, IgD, and IgE. Ig is the abbreviation for immunoglobulin, or antibody.

IgG antibodies are the most common and the most important. They circulate in the blood and other body fluids, defending against invading bacteria and viruses. The binding of IgG antibodies with bacterial or viral antigens activates other immune cells that engulf and destroy the antigens. The smallest of the antibodies, IgG moves easily across cell membranes. In humans, this mobility allows the IgG in a pregnant woman to pass through the placenta to her fetus, providing a temporary defense to her unborn child.

IgA antibodies are present in tears, saliva, and mucus, as well as in secretions of the respiratory, reproductive, digestive, and urinary tracts. IgA functions to neutralize bacteria and viruses and prevent them from entering the body or reaching the internal organs.

IgM is present in the blood and is the largest of the antibodies, combining five Y-shaped units. It functions similarly to IgG in defending against antigens but cannot cross membranes because of its size. IgM is the main antibody produced in an initial attack by a specific bacterial or viral antigen, while IgG is usually produced in later infections caused by the same agent.

Words to Know

Allergen: A foreign substance that causes an allergic reaction in the body.

B cells: Cells produced in bone marrow that secrete antibodies.

Immune response: The production of antibodies in response to foreign substances in the body.

Immunity: The condition of being able to resist the effects of a particular disease.

Immunization: The process of making a person able to resist the effects of specific foreign antigens.

Inoculate: To introduce a foreign antigen into the body in order to stimulate the production of antibodies against it.

Monoclonal antibodies: Identical antibodies produced by cells cloned from a single cell.

Proteins: Large molecules that are essential to the structure and functioning of all living cells.

Vaccine: Preparation of a live weakened or killed microorganism of a particular disease administered to stimulate antibody production.

IgD is present in small amounts in the blood. This class of antibodies is found mostly on the surface of B cells—cells that produce and release antibodies. IgD assists B cells in recognizing specific antigens.

IgE antibodies are present in tiny amounts in serum (the watery part of body fluids) and are responsible for allergic reactions. IgE can bind to the surface of certain cells called mast cells, which contain strong chemicals, including histamine. (Histamines are substances released during an allergic reaction. They cause capillaries to dilate, muscles to contract, and gastric juices to be secreted.) When an allergen such as pollen binds with its specific IgE antibody, it stimulates the release of histamine from the mast cell. The irritating histamine causes the symptoms of an allergic reaction, such as runny nose, sneezing, and swollen tissues.

Tests that detect the presence of specific antibodies in the blood can be used to diagnose certain diseases. Antibodies are present whenever antigens provoke an immune reaction in the test serum.

The immune response

When a foreign substance enters the body for the first time, symptoms of disease may appear while the immune system is making antibodies to fight it. Subsequent attacks by the same antigen stimulate the immune memory to immediately produce large amounts of the antibody originally created. Because of this rapid response, there may be no symptoms of disease, and a person may not even be aware of exposure to the antigen. They have developed an immunity to it. This explains how people usually avoid getting certain diseases—such as chicken pox—more than once.


Immunization is the process of making a person immune to a disease by inoculating them against it. Inoculation is the introduction of an antigen into the body—usually through an injection—to stimulate the production of antibodies.

The medical practice of immunization began at the end of the eighteenth century, when English physician Edward Jenner (1749–1823) successfully used extracts of body fluid from a dairymaid (a woman employed in a dairy) infected with cowpox (a mild disease) to inoculate a young boy against smallpox, a then-common and often fatal viral disease. Jenner called his method "vaccination," using the Latin words vacca, meaning "cow," and vaccinia, meaning "cowpox." Because the two diseases are caused by similar viruses that have the same antigens, antibodies that work against cowpox will also fight smallpox.

In 1885, a rabies vaccine developed by French scientist Louis Pasteur (1822–1895) from the spinal fluid of infected rabbits proved to be successful. Since that time, vaccines have been developed for many diseases, including diphtheria, polio, pertussis (whooping cough), measles, mumps, rubella (German measles), hepatitis, and influenza. Vaccines are made from either weakened live or killed microorganisms. When introduced into the body, they stimulate the production of antibodies, providing active immunity against bacterial and viral diseases.

Monoclonal antibodies

Monoclonal ( mono means "one") antibodies are identical antibodies produced by clones (exact copies) of a single cell. The cell from which the clones are made is created by combining a B cell containing a specific antibody with a myeloma (a form of cancer) cell. The resulting hybrid produces the specific antibody of the parent B cell and divides indefinitely like the parent cancer cell. Clones of the hybrid cell produce virtually unlimited amounts of one type, or monoclonal, antibodies. Monoclonal antibodies are used in many medical diagnostic tests, such as pregnancy tests, and in the treatment of cancer and other diseases.

Autoimmune Disease

Autoimmune diseases occur when the body's immune system loses the ability to recognize the difference between self and nonself. This results in the body producing antibodies, called autoantibodies, against its own tissues. Normally, antibodies are only produced against microorganisms that invade the body. The inability to make a distinction between self and nonself may lead to the destruction of body tissue and result in a number of chronic, debilitating diseases.

The cause of autoimmune reactions is not known. It is thought that infection by viruses and bacteria may trigger an autoimmune response. In addition, exposure to certain chemicals and ultraviolet light may alter proteins in the skin; the body may then become sensitive to these proteins and produce autoantibodies against them. Certain individuals seem to be genetically predisposed to have autoimmune responses. Some diseases that are associated with autoimmune responses are rheumatoid arthritis, lupus erythematosus, and pernicious anemia.

[ See also Allergy ; Blood ; Immune system ; Rh factor ; Transplant, surgical ; Vaccine ]

User Contributions:

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Feb 17, 2009 @ 12:12 pm
Wow this article is quite very useful . Thank You very much
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Jul 20, 2010 @ 6:06 am
I agree this was very informative and easily understood. Thank you for writing and putting on web where I could find it! :)
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Aug 25, 2010 @ 4:16 pm
Can you please link on how antigens produce effects against infecious organism.Your work is highly appreciated.
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Sep 28, 2010 @ 11:11 am
Hello. If you injected four different types of cells from a donar into a recipient---cells from different organs---would the recipient
product specific antibodies against each one? So if you injected normal prostate cells into someone else and cancerous prostate cells
would the recipient produce two different specific antibodies against both? Or does it see the cells as simply not-self?

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Nov 17, 2010 @ 11:23 pm
really thanks for that very good article
Ahmed Elhaged
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Jan 10, 2011 @ 10:22 pm
Please tell me about 'Bone Marrow Transplant & its applications.'
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Feb 12, 2011 @ 2:02 am
I am scheduled for surgery on the 17th, I was called by the hospital lab that I needed to have my blood work repeated due to (I believe she said) matching ? the antigens. If I have a problem with antigens, would that affect having surgery and if so, what can be done to cure the problem?
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Feb 19, 2011 @ 7:07 am
So , without a virus there would be no antigen produced , therefore , if it was a specific antibody that was detected , then a specific virus would be producing a specific antigen ?
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Apr 7, 2011 @ 1:13 pm
great article if ound it really interesting and it really helped me with a lab report on antigens and antibodies. LIke bobby im curious as to how to reference it.
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Apr 22, 2011 @ 11:11 am
the content is nice ,it would have beter if the content was with pictorial explanation,any way nice
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Jun 9, 2011 @ 1:13 pm
The article is very informative and cleared all the doubts i head.Its in simple terms that would help undergraduates too.It helped me in my lectures and i am grateful to you for publishing such an informative article.
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Nov 30, 2011 @ 9:09 am
very helpful article and easy to understand as well..
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May 17, 2012 @ 1:13 pm
Thanks for the article, its educative. what part of the immune system produces antibody against HIV virus?
Adeniyi Gideon
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Sep 13, 2012 @ 10:22 pm
Thanks! It was well explained. Pictorial explanation will be highly appreciated.
ankita wagle
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Oct 11, 2012 @ 11:23 pm
hello my question is when we electophoresed igG it moves towards cathode so whats the reason because all proteins have equal charge . will u pls explain my question
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Feb 20, 2013 @ 1:01 am
plz explain me what kind of antibodies that are produced regarding the cause of TB?
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Feb 21, 2013 @ 12:00 am
if antigen A is present then antibody B how developed or vice versa
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Jun 26, 2013 @ 12:00 am
Thank you for the article,easy to understand. also please include "how the antibody inactivates the antigen? i have a little confusion over there". Thank you
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Jul 6, 2013 @ 10:22 pm
Hello, I am trying to find out what causes your blood to stop producing IgG & IgA? I've been receiving IVIG Infusions, but I really need to get to the root of this . I can't live the rest of my life needing these treatments! It has also caused me to have a secondary dx of CIDP, I have been seen by top notch doctors,had every test & marrow biopsy done. I don't know where to turn for help. Thank you for your gear article .
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Mar 17, 2014 @ 3:15 pm
Wow this was an amazing article, very informative and very easy to understand. Thank you!
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Apr 13, 2014 @ 5:17 pm
This information was very simple to me in understanding the Immune system of our body. It was well comprehended, thanks.
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May 24, 2014 @ 10:22 pm
how the immunologbuline identify the foreign body?
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Jun 14, 2014 @ 8:20 pm
Hi I have a question :) What are the 5 ways that an antibody destroys or inactivates an antigen ? Thank you ^_^

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