Antigen Vs. Antibody: Understanding The Difference - Healthline

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HealthlineSubscribeWhat’s the Difference Between Antigens and Antibodies?

Medically reviewed by Jennie Olopaade, PharmD, RPH — Written by The Healthline Editorial Team and Leilani Fraley, RN, MSN on March 4, 2021

Antigen
Antibody
Vaccinations
Antibody testing
Bottom line

Antigens and antibodies play vital but distinct roles in illness and disease. One tries to wreak havoc on our health while the other fights to protect it.

Simply put, antigens can make you sick, and antibodies are how your body defends itself against antigens.

Read on to find out the important role antigens and antibodies play in your health and how they do it.

What is an antigen?

Antigens, or immunogens, are substances or toxins in your blood that trigger your body to fight them.

Antigens are usually bacteria or viruses, but they can be other substances from outside your body that threaten your health. This battle is called an immune response.

The presence of antigens rouses your body’s illness-fighting white blood cells, called lymphocytes. This presence of antigens causes white blood cells to make cells called antibodies to fight against the antigens.

There are two main types of antigens, heteroantigens and autoantigens:

Heteroantigens are substances that are foreign to your body and involve substances made by or found within:
- viruses
- bacteria
- protozoa
- blood and red blood cells from other people
- snake venom
- allergens such as pollen
- certain proteins in foods

Autoantigens, or self-antigens, are made by your body to fight your cells and are usually a sign of an illness such as an autoimmune condition.

Read this for more information about different types of autoimmune conditions.

What is an antibody?

Antibodies are also called immunoglobulins or Ig. They are Y-shaped proteins made by your immune system’s B lymphocytes or B cells.

B cells attack and eliminate viruses and other toxins outside the cell. They do this by making specific antibodies for a single type of antigen.

These tailored antibodies lock on to their specific antigens and tag them for attack. Antibodies also block these antigens, keeping them away from your healthy cells. Ultimately, antibodies kill these antigens, stopping infection.

The main types of antibodies (immunoglobulins) include:

IgG. These are the most abundant types of antibodies in your plasma. They detoxify harmful substances and provide long-term protection.
IgM. These are the first antibodies made by B cells in response to antigens.
IgA. These antibodies collect antigens and remove them from your body in your mucus or other body fluids.
IgE. These antibodies trigger allergies and protect against parasites. Small amounts are in your skin, lungs, and mucosal membranes.
IgD. These antibodies bind to B cells and signal them to release IgM antibodies.

Each antibody guards against its target antigen, and many types of antibodies are found throughout your body. They play a vital role in your body’s defense against illness and disease.

How are antigens and antibodies used in vaccinations?

Vaccines work by imitating antigens that trigger infection without causing illness so that, if the infection mimicked by the vaccine enters your body again, your body already has what it needs to protect you.

Traditional vaccines

Vaccines include weakened or inactive parts of antigens from viral infections like the flu. These inactive antigens trigger your B cells to make targeted antibodies to fight that specific infection.

Read this for more information about flu vaccines.

Newer vaccines include the genetic blueprints for making antigens instead of using actual antigen components, but they work much in the same way.

Vaccines boost the number of antibodies in your body against a specific antigen. When a vaccine enters your body, your B-cells respond as if a naturally occurring antigen has attacked your body.

The B-cells respond to the vaccine by reproducing themselves to form an army of cells that are programmed to react to the antigens in the vaccine.

The antibodies created by the vaccine lie dormant in your body until you contract an infection from that antigen, and then they are called to action.

If you contract an infection, antibodies called memory B cells quickly reproduce and make the specific antibodies you need to destroy that antigen.

The memory B-cells’ response is called a secondary immune response, and it’s much faster and more effective than the reaction your body would have to the infection if you had not been vaccinated.

How are antigens and antibodies used for COVID-19 testing?

According to the FDA, there are three main types of testing for COVID-19 and SARS-CoV-2, the virus that causes it:

Molecular tests. These tests measure genetic material from a virus that is in your body. Material for testing is collected from your nose or throat using a long swab. If the test result is negative, it means you do not have the SARS-CoV2 virus or the COVID-19 infection during the testing period. The test may be wrong if you have a very low level of the virus because your development of the COVID-19 infection is very recent.

Antigen tests. These tests measure antigen proteins from the virus. Material for testing is collected from your nose or throat using a long swab. Most rapid COVID-19 tests are antigen tests. These tests can diagnose COVID-19 but may not be able to rule out a current, active infection. If an antigen test is negative, you will need a molecular test to confirm that you do not have COVID-19.

Antibody tests. These tests measure antibodies in the blood. Material for testing is collected by a blood test from drawing blood at your arm or from a finger stick. Depending on which antibodies are being measured, these tests can tell if your body has begun to fight a COVID-19 infection or if you’ve had an infection for several days. They are good for determining if you’ve had COVID-19 for a period of time. However, they may not be a reliable way to tell if you have a current infection. They are also not a reliable way to be sure you do not currently have COVID-19. Additional testing may be needed to exclude an infection.

Read this for more information about SARS-CoV-2 and COVID-19 testing.

The bottom line

Antigens trigger your immune system to launch an antibody response. Specific antibodies detect specific antigens. This means each antibody wages war against one target antigen. Once antibodies detect antigens, they bind and neutralize them.

This knowledge is stored in your immune system’s long-term memory. It launches fights against the antigen should it attempt to attack your body again.

The distinct functions of antigens and antibodies are used to create tests and vaccines that help detect and combat illness and disease.

How we reviewed this article:

SourcesHistoryHealthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

Antigen-detection in the diagnosis of SARS-CoV-2 infection using rapid immunoassays. Interim guidance. (2020).https://www.who.int/publications/i/item/antigen-detection-in-the-diagnosis-of-sars-cov-2infection-using-rapid-immunoassays
Coronavirus testing basics. (2020).https://www.fda.gov/media/138094/download
COVID-19. (n.d.).https://www.cdc.gov/coronavirus/2019-nCoV/index.html
Dan JM, et al. (2021). Immunological memory to SARS-CoV-2 assessed for up to 8 months after infection.https://science.sciencemag.org/content/371/6529/eabf4063
Deeks JJ, et al. (2020). Antibody tests for identification of current and past infection with SARS-CoV-2.https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD013652/full
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Ibarrondo FJ, et al. (2020). Rapid decay of anti-SARS-CoV-2 antibodies in persons with mild Covid-19.https://www.nejm.org/doi/10.1056/NEJMc2025179
Isho B, et al. (2020). Persistence of serum and saliva antibody responses to SARS-CoV-2 spike antigens in COVID-19 patients.https://immunology.sciencemag.org/content/5/52/eabe5511.long
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Lederer K, et al. (2020). SARS-CoV-2 mRNA vaccines foster potent antigen-specific germinal center responses associated with neutralizing antibody generation.https://www.cell.com/immunity/fulltext/S1074-7613(20)30496-9?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS1074761320304969%3Fshowall%3Dtrue
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Perreault J, et al. (2020). Waning of SARS-CoV-2 RBD antibodies in longitudinal convalescent plasma samples within 4 months after symptom onset.https://ashpublications.org/blood/article/136/22/2588/463996/Waning-of-SARS-CoV-2-RBD-antibodies-in
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Medically reviewed by Jennie Olopaade, PharmD, RPH — Written by The Healthline Editorial Team and Leilani Fraley, RN, MSN on March 4, 2021

Antigen Vs. Antibody: Understanding The Difference - Healthline

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What is an antigen?

What is an antibody?

How are antigens and antibodies used in vaccinations?

Traditional vaccines

How are antigens and antibodies used for COVID-19 testing?

The bottom line

How we reviewed this article:

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