Antibodies are protective proteins produced by your immune system. They attach to antigens (foreign substances) — such as bacteria, fungi, viruses and toxins — and remove them from your body.


What are antibodies?

Antibodies are proteins that protect you when an unwanted substance enters your body. Produced by your immune system, antibodies bind to these unwanted substances in order to eliminate them from your system.

Another word for antibody is immunoglobulin.

Antigen vs antibody

An antigen is a foreign substance that enters your body. This can include bacteria, viruses, fungi, allergens, venom and other various toxins. An antibody is a protein produced by your immune system to attack and fight off these antigens.


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

How do antibodies fight off antigens?

The molecules on the surfaces of antigens differ from those found naturally in your body. So, when an antigen enters your body, your immune system recognizes it right away. In order to attack this antigen invader, your immune system calls out for antibody protection.

Where are antibodies produced?

Antibodies are produced by B cells (specialized white blood cells). When an antigen comes into contact with a B cell, it causes the B cell to divide and clone. These cloned B cells — or plasma cells — release millions of antibodies into your bloodstream and lymph system.

Antibodies are located in various areas of your body, including your skin, lungs, tears, saliva and even breast milk. In fact, high amounts of antibodies are present in colostrum (a thick fluid secreted by the breasts for a few days after giving birth). That’s why breastfeeding (chestfeeding) can boost your baby’s immune system.


What are monoclonal antibodies?

Monoclonal antibodies are created in a lab. They mimic your immune system’s natural ability to fight off pathogens. Using monoclonal antibodies to fight infections is a type of immunotherapy.


What are the 5 types of antibodies and their function?

Antibodies are categorized into five classes according to their location. Each one is labeled by a letter, which is attached to an abbreviation of the term “immunoglobulin” (Ig):

Antibody Type
Found in saliva, tears, mucus, breast milk and intestinal fluid, IgA protects against ingested and inhaled pathogens.
This antibody is found on the surface of your B cells. Though its exact function is unclear, experts think that IgD supports B cell maturation and activation.
Found mainly in your skin, lungs and mucus membranes, IgE antibodies cause your mast cells (a type of white blood cell) to release histamine and other chemicals into your bloodstream. IgE antibodies can cause allergic reactions.
This is the most common antibody, making up approximately 70% to 75% of all immunoglobulins in your body. It’s found mainly in blood and tissue fluids. IgG antibodies help protect your body from viral and bacterial infections.
Found in your blood and lymph system, IgM antibodies act as the first line of defense against infections. They also play a large role in immune regulation.


What are antibodies made of?

Antibodies are proteins. Each antibody has four polypeptides (peptides that consist of two or more amino acids), including two heavy chains and two light chains.

What do antibodies look like?

Each antibody structure consists of two heavy chains and two light chains, which join to form a Y-shaped molecule. Each type of antibody has a different amino acid sequence at the tips of the “Y” which is why each antibody is shaped differently.

Conditions and Disorders

What conditions can monoclonal antibodies treat?

Each type of monoclonal antibody targets a specific antigen. As a result, monoclonal antibodies can treat a number of health conditions, including:

What are COVID antibodies?

Antibodies to the virus that causes COVID-19 can be found in the blood of people who have recovered from the infection or those who have received the COVID-19 vaccine. If you’ve already had COVID-19, getting the vaccine increases your body’s antibody response and improves your protection against the virus.

How can I tell if I have COVID antibodies?

You can take an antibody test to find out if you have COVID antibodies. Antibody tests are available at laboratories and some pharmacies. You can also obtain them from your healthcare provider.

How long do COVID antibodies last?

Research is still ongoing, but studies show that people who had COVID-19 have antibodies for at least five to six months. One study found that people who’ve recovered from COVID-19 have memory B cells, which can stay in your body for years and target the virus specifically. This means you’ll be able to produce antibodies quickly if you’re exposed to the virus again.

What are thyroglobulin antibodies?

Thyroglobulin antibodies are often found in people who have thyroid problems, such as hyperthyroidism or hypothyroidism. These antibodies target thyroglobulin proteins (precursors of thyroid hormones) and can potentially destroy the thyroid gland.

What is an antithyroglobulin antibody test?

If your healthcare provider suspects thyroid problems, they may recommend an antithyroglobulin antibody test. This test is also performed to monitor progress after thyroid cancer treatment.

What if I test positive for antithyroglobulin antibodies?

If antithyroglobulin antibodies are found in your blood, then it could indicate thyroid problems, including:

What are autoantibodies?

Also known as antinuclear antibodies (ANAs), autoantibodies target normal proteins in a cell’s nucleus. Autoantibodies mistake normal, healthy proteins as dangerous and unwanted. As a result, your body begins attacking itself. Most people have small amounts of autoantibodies. In large quantities, however, autoantibodies usually indicate an autoimmune disease.

How can you test for antinuclear antibodies?

A blood test called the fluorescent antinuclear antibody test is the most common way to test for antinuclear antibodies. During this test, your healthcare provider views fluorescent-labeled antibodies under a microscope to determine the intensity and pattern of the fluorescence. This test is commonly used to rule out lupus.

What does a positive ANA test mean?

A positive ANA test result tells your healthcare provider to keep looking for a diagnosis. It doesn’t necessarily mean that you have an autoimmune disease. If you get a positive result, then your provider will likely recommend further testing.

A note from Cleveland Clinic

Antibodies are your immune system’s way of protecting you from infections, allergens and toxins. Your body produces these proteins naturally. Sometimes, lab-made monoclonal antibodies are used to treat certain health problems, such as cancer, heart disease, rheumatoid arthritis and more.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 05/06/2022.

Learn more about our editorial process.

Cancer Answer Line 866.223.8100