Antibody vs. Antigen: What Are the Differences?

If you aren’t a medical professional, then you probably have heard the words antigen and antibody before, but don’t necessarily know what they mean. Most people have a general idea of what antibodies do, but they don’t realize their crucial relationship with antigens. In this article, we’ll take a closer look at the difference between these two, what their functions are, and how they are used in medical procedures.

What Are the Differences Between Antigen and Antibody?

The easiest way to get a better idea for the difference between antigen and antibody is to take a look at a close comparison of the two. They have different structures, functions, and locations within the body. One is generally considered a good thing to have as it protects your body while the other can provoke a negative reaction.




What Is It?

An antigen is a foreign particle that can create an immune response within a person’s body. They are also known by the term immunogenicity and can include pollen, viruses, bacteria, or chemicals.

Antibodies are also known as immunoglobulins and these proteins are created by the body. They work to fight against the antigens.

What Does It Look Like?



Chemical Components

Antigens are mostly made up of proteins, but they may also be nucleic acids, carbohydrates, or lipids.

Antibodies are proteins.

Different Types and Their Functions

Antigens are typically divided into self and non-self-antigens. Self-antigens, like cancer cells, form within the body. Non-self-antigens come from outside the body. They stimulate your immune system to produce more antibodies, exemplifying the difference between antigen and antibody.

There are a total of 5 types of antibodies, each of which is different. They are IgA, IgE, IgG, IgM, and IgD.


IgA protects the surfaces of the body which receive exposure to foreign, outside substances.


IgE causes a reaction in the body against foreign substances, including animal dander, pollen, and fungus spores. These antibodies are part of allergic reactions to some poisons and certain medications. Those with allergies tend to have high quantities of this type of antibody.


IgG plays a key role in fighting infections of a bacterial or viral nature. These are the only antibodies that are able to cross the placenta of a pregnant woman, offering protection to the fetus while still in utero.


When an infection occurs, IgM antibodies are the very first type of antibodies to be made as a response. They will lead to other cells in the immune system destroying foreign substances.


Experts are still unclear as to what exactly IgD antibodies do.

Where Can They Be Found?

Another difference between antigen and antibody is where they are. Antigens are “hooks” on the surface of cells and are found in nearly every cell.

You can find IgA antibodies in the vagina, eyes, ears, digestive tract, breathing passages, and nose, as well as in blood, tears, and saliva. Approximately 10-15% of antibodies within the body are IgAs. There are a small amount of people who do not make IgA antibodies.


IgD antibodies can be found in smaller quantities within tissue linings of the chest or belly.


You will find IgE antibodies in the mucous membranes, skin, and lungs.


IgG antibodies ae found in all of the body fluids. They are the most common antibodies within the body as well as the smallest.


IgM antibodies are the biggest of the antibodies and can be found in the lymph fluid and blood. They account for 5-10% of antibodies within the body.

How Do Antigens and Antibodies Work: The Immune Response

To better understand the difference between antigen and antibody, it helps to become familiar with the immune response. All healthy adults have thousands of various antibodies in small amounts throughout their body. Every antibody is very specialized, recognizing a single type of foreign substance. Most antibody molecules are shaped like a Y, featuring a binding site along each arm. Each binding site has a specific shape and only antigens with the same shape will fit in. Antibodies are designed to bond with the antigens. When binding, they make the antigens inactive, letting other processes in the body take over the foreign substances, removing and destroying them.

The first time a foreign substance enters the body, you may experience disease symptoms. This occurs when the immune system creates antibodies that will fight the foreign substance off. When the same antigen attacks again in the future, the attack stimulates immune memory. This leads to immediate large production of the antibody that was created the first time the attack occurred. The rapid response to further attacks means that you may not experience any disease symptoms or even know that you were exposed to the antigen. Some people may have also developed immunity to the foreign substance. This is why most people will only get diseases like chicken pox once in their lives. 

To better understand the immune response, watch this video:

Medical Applications

Apart from the above-mentioned difference between antigen and antibody, a test for antibodies could provide useful information in the diagnostic process. Your doctor may test your blood for antibodies for a range of reasons including:

  • Screen for allergies or autoimmune diseases.
  • Check for a current infection or the presence of one in the past.
  • Determine whether recurring infections occur because of low levels of IgG antibodies or other immunoglobulins.
  • Check for an immunization response as a way to see whether you are still immune to a particular disease.
  • Check on the treatment for various cancers, such as those affecting a person’s bone marrow.
  • Search for specific types of cancer, including macroglobulinemia or multiple myeloma.
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