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Antibodies are glycoproteins which are produced in response to the presence of specific Antigens and to counteract them. Antigens are often harmful foreign substances which stimulate the presence of antibodies by provoking an immune response.
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Keyterms: Antibodies, glycoproteins, Antigens, nucleic acids, bacteria, fungi, viruses, immunogens, plasma cells, Immune system, Immunity
Read More: Deficiency symptoms
Antigens and Antibodies
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Antigen is a molecule containing proteins within itself. It may be a foreign substance, chemicals or even bacteria inside the body. These enable the body to make antibodies so as to develop an immunity. Antigens play a very important role in prevention and elimination of diseases so as to protect the body against any harm. Antigens are commonly known as immunogens. Examples - nucleic acids, bacteria, fungi, viruses.
Antigens and Antibodies
Antibodies contain proteins too. They are also called immunoglobulins. These are prepared by plasma cells in response to an antigen. They have the ability to bind themselves to specific antigens so as to fight infections. These originate inside the body and can be found in very few cells.
There are five major types of antibodies described further. Examples - breast milk, sweat, mucous, etc.
Nature of Antigens
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Antigens may be composed of protein, polysaccharides or nucleic acids. They can even be lipids.
Proteins: It has been found that a majority of immunogens happen to be proteins. It is a good thing because proteins have proved to be extremely good immunogens.
Polysaccharides: Pure polysaccharides are good immunogens. These are basically carbohydrates consisting of closely bonded sugar molecules. Even liposaccharides come under this category.
Nucleic acids: They have very few immunogens in them. This can be changed when they are mixed with proteins. They will be more effective this way.
Lipids: lipids are hydrocarbons containing molecules and provide energy for tissues. These are non-immunogenic in general.
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Antigen Types
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Antigens can be classified on two criteria: Origin and Immune Response
On Basis of Origin
Antigens are of three types on the basis of their origin:
Exogenous Antigen: These are antigens which enter the body preferably from outside. This may be through the form of inhalation or ingestion. Bateria, fungi, pollen are common examples of this antigen.
Endogenous Antigen: These are already present in the body. These antigens are already generated within earlier cells because of infections. This happens as a result of normal cell metabolism. Examples of endogenous antigens include blood group antigens, HLA( Histocompatibility Leukocyte Antigens ), etc.
Autoantigen: An autoantigen is a self protein or complex of proteins which due to certain genetic reasons may be attacked as their own immune system. Nucleic acids and nucleoproteins fall under this category.
Antigens and Antibodies
On Basis of Immune Response
On the basis of their immune response, antigens are of two types.
Complete Antigen/Immunogen: These antigens have the ability to create immune responses by themselves and have some antigenic properties. These may be proteins or even polysaccharides.
Incomplete Antigen /Hapten: These are foreign particles and can react separately with corresponding antibodies. They don't contain protein within and are unable to create an immune response by itself. Examples are capsular polysaccharide of pneumococcus, cardiolipin antigens, etc.
On Basis of Immune Response
Functions of Antigens
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- It provides immunogenicity by way of creating or inducing an immune response in the body.
- Antigens also provide immunological reactivity which helps develop a specific reaction with antibodies or sensitized cells. Sensitized cells are cells which have already been exposed to antigens.
- They have the ability to react separately with specific antibodies.
- Some antigens like hapten, are unable to create response by itself but can achieve this when a carrier protein comes along.
Nature of Antibodies
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- Their molecular weight ranges from 150000 - 950000
- An immunoglobulin molecule is made up of 4 polypeptide chains. Out of these two are heavy chains, and two are light chains.
- They consist of the gamma globulin portion of the blood protein.
- They are easily soluble.
- They are secreted by activated B cells and plasma cells in response to an antigen.
- They have the capability to bind with specific antigen.
Read Also: Acquired Immunodeficiency Syndrome
Antibodies: Types
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Antibodies are mainly of five types:
IgM
- Monomer serves as a B-cell receptor.
- It has a life of about 5 days.
- A deficiency of IgM can lead to septicemia. This is the clinical name for blood poisoning by bacteria.
- It moves around in the blood and lymph.
- It is the largest antibody and is highly potent as compared to IgG.
IgG
- This has been classified into 4 types - IgG1, IgG2, IgG3 and IgG4.
- It exists in polymerised form and has a life of 25 days.
- It is distributed equally in the intravascular wall.
- It strengthens the process of phagocytosis.
- It is normally transported across the placenta and provides natural passive immunity in the newborn.
- It helps neutralize toxins and viruses.
IgA
- It is found in saliva, tears and the colostrum.
- It has a lifespan of 6-8 days.
- It gives immunity against intestinal pathogens.
- It promotes phagocytosis and intracellular killing of MCO.
- It occurs in two forms- Serum IgA and Secretory IgA.
- It has been found effective against influenza virus.
IgD
- It's a monomer.
- It has a life of about 3 days.
- These can be found lying above B-lymphocytes.
- It acts as a receptor for antigen binding.
IgE
- It has a very small quantity of blood.
- It contains a minute amount of lymphocytes.
- It is responsible for hypersensitivity.
- They respond very well to allergic reactions.
- It's a monomer.
Functions of Antibodies
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- Provides defense mechanisms against deadly diseases like polio, influenza, salmonella, etc.
- It is present actively in breast milk and helps protect newborns in their early stages of life.
- Bind to inactivate foreign substances like pathogens.
- Help in phagocytosis.
- Assists in neutralizing the effects of bacteria and toxins.
- Provide long term protection against pathogens.
Antibodies
Difference Between Antigens and Antibodies
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| Antigens | Antibodies |
|---|---|
| These are also called Immunogens. | Antibodies are also called Immunoglobulins. |
| These are basically lipids, but also can be proteins, carbohydrates and nucleic acid. | These are glycoproteins made of carbohydrates and amino acids. |
| They form either inside the body or outside the body. | These are found to have been generated within the body itself. |
| These are epitopes by specific binding site. | Antibodies happen to be paratopes. |
| These cause allergic reactions and can also cause illness. | These protect us against the effects of antigens by inactivating them. |
| These exist in all kinds of cells. | These can be found in a very limited number of cells. |
| The source of antigens are mostly a foreign substance like fungi or bacteria. | Antibodies are produced by the body’s very own B cells. |
| There are 3 main kinds of antigens. | Antibodies have been classified broadly into five categories. |
| Examples - bacteria, viruses, Blood group antigens, HLA, Nucleoproteins, Nucleic acids. | Examples - Breast milk, tears, saliva, sweat, and mucus. |
Difference Between Antigens and Antibodies
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Things to Remember
- Antigens are substances which induce an immune response in the body so as to fight the foreign particle. Antigens are also called immunogens. These may arise within the body or from outside the environment. All antigens are not protein by nature. Some may be in the form of polysaccharides, lipids or even nucleic acids. Example - bacteria, virus, fungi, etc.
- Antibodies are basically glycoproteins which originate inside the body so as to provide a defense mechanism and help eliminate toxins. Antibodies are popularly known as immunoglobulins and have been divided into five kinds. These are IgM IgM IgA IgD and IgE. Each one of them has its own unique function and role.
- Keeping our immune system healthy is very important especially now with all these diseases around us. We often get fevers when we get sick. However we should keep in mind that fevers are good. During this time they give out white blood cells and increase the body’s metabolism. When we have fevers, it means our body is doing its job.
- Stress has serious effects on our body. If the levels of depression and stress in the body starts increasing rapidly, then we develop more chances of being affected by diseases. It can cause problems like indigestion, gain in weight, disturbances in sleeping patterns, heart diseases and even difficulty in remembering things. We can find a way out of this by practicing yoga, meditation, eating healthy and working out regularly. Even talking it out to other people helps a lot.
Previous Year Questions
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Sample Questions
Ques. What are antigens? What is their function? (2 Marks)
Ans. Antigens are proteins, lipids, polysaccharides or even lipids which help induce an immune response in the body. They are also called immunogens and can originate inside the body as well as enter from outside. Bacteria, fungi, nucleic acids are some common examples.
Ques. What is the structure of antigens? (2 Marks)
Ans. An antigen consists of several epitopes. An antibody has the ability to bind itself to specific epitopes on antigens. These have the ability to create an immune response and generate specially sensitized cells. It's important to remember that only a few antigens are capable of activating lymphocytes.
Ques. What happens if antigens in your body become low? (2 Marks)
Ans. If antigens start decreasing in our body, it is very likely that we suffer from some infection or disease again and again.
Ques. What are antibodies? (2 Marks)
Ans. Antibodies are Y-shaped proteins and they help the body by eliminating and destroying the infection causing bacteria. These are produced in the body so as to provide protection against a certain disease or infection.
Ques. What is immunity? (2 Marks)
Ans. The immune system of our body is a defense mechanism. It fights germs and protects the body so as to keep us healthy. When the body has the capability to prevent such attacks, it is said to be immune. We can say immunity is basically the state of being immune.
Ques. What are types of immunity? (2 Marks)
Ans. There are three kinds of immunity. These are -
- Innate immunity - This is the kind of immunity which is already present in an individual during birth.
- Adaptive immunity - We develop this kind of immunity in our life many times. For example when people became exposed to polio virus they started taking polio vaccine so as to be immunized against it.
- Passive immunity - We borrow this immunity from another source. It lasts for a short duration.
Ques. How can we increase antibodies in our body? (2 Marks)
Ans. Eating more veggies increases the chance of the antibodies in our body. Apart from this, taking a probiotic supplement, drinking lots of water, keeping stress and anxiety levels in check, working out regularly. It's also very important to get enough sleep as studies have found that lack of sleep makes a person prone to getting more sick than those who get plenty of sleep.
Ques. How can we boost our immune system? (2 Marks)
Ans. Limiting alcohol, including plenty of fruits like tangerines, oranges in meals, and cooking with olive oil helps strengthen our immune system. We can even take supplements like zinc and vitamin C tablets. Eating more greens like spinach, broccoli also helps a lot.
Ques. What makes antibodies disappear in our body? (2 Marks)
Ans. When our body suffers an infection, it's possible that some antibodies will break down into plasma cells. Being protein by nature, these antibodies start disappearing from the body within a few months.
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