Antigens: Overview, Immune System, and Function


An antigen is a molecule that stimulates the immune response by activating white blood cells (white blood cells) that fight disease. Antigens can be present on invaders such as bacteria, viruses, parasites, fungi, and transplanted organs, or abnormal cells such as cancer cells. Learn more about antigens and how the immune system interacts with them to protect it.

KTSDESIGN / Science Photo Library / Getty Images

The immune system

The human body relies on certain defense mechanisms to help contain disease. The immune system triggers a response that produces cells and proteins to fight infection.

There are two types of immunity in the body: innate and acquired.

  • Innate immunity is a type of non-specific defense against pathogens. It reacts quickly to the pathogen, but is unable to remember individual threats and create specific defenses if they reappear.
  • Acquired immunity is the part of immunity that helps differentiate between different types of threats. Acquired immunity works more slowly than congenital immunity, but it remembers the antigen and reacts to it quickly and selectively if it is re-exposed.

How does it work

The body must be able to recognize what belongs and what does not, and antigens are an important part of this process. When the body identifies an antigen, it initiates an immune response.

When white blood cell receptors bind to antigens, they cause the white blood cells to multiply and trigger an immune response.


Antigens can be divided into two main groups: foreign antigens and self-antigens.

Foreign antigens

This type, also known as heteroantigens, comes from the outside and is present in bacteria, viruses, snake venom, some food proteins, and other people's cells.


Autoantigens are already present in the body and should not trigger an immune response in healthy people, because the body needs to know that they are not harmful. However, sometimes the body mistakenly acts against them, leading to autoimmune inflammation.

Role of antigens

Antigens are the initiators of the immune response. They can bind to white blood cells, including white blood cells, which are cells of the adaptive immune system.

Leukocytes include B cells and T cells. B cells produce antibodies that can also bind to antigens. Once the antigen binds to the B cell receptor, the antibodies are produced.


A vaccine is a medical injection or pill that contains a protein or a weakened or killed version of a pathogen. Vaccines are used to create an immune response in the body against a specific antigen.

When the immune system creates specific antibodies, such as influenza antibodies, it makes your body ready and well equipped to fight the influenza virus if it is exposed later, using the antibodies created earlier.

Once vaccinated, your antibodies must remain ready to fight infection for many years.

With a viral infection

In a viral infection, such as seasonal flu, the immune system responds by producing antibodies that can bind to a specific antigen. This process works in the same way as with a vaccine, although the infectious viral microbes are much stronger.

The antigens of an infectious virus signal an immune response by causing the body to produce antibodies against a particular strain of viral infection. These antibodies then use what's called immune memory to help you fight infection if you're exposed again.

Immune memory is the ability of your immune system to prevent future illness from the same strain of disease by using antibodies that it has previously created in response to antigens.

Role of antibodies

Antibodies are created by cells of the immune system. They bind to antigens and promote the elimination of dangerous pathogens from the body. They neutralize the threat by warning other parts of the immune system to take over.


Antigens are an important part of the immune response because they help your body recognize harmful threats and get rid of them.

Relevance of the evidence

Antigen and antibody tests can be performed on blood samples. These tests can help diagnose disease, prevent immune reactions, or check if you have responded to the vaccine.

Antigen test

Antigen tests are used to diagnose diseases that are currently present in the body.

For example, with regard to COVID-19, antigen tests can determine if a person is currently ill with the virus. This is important to prevent the spread of the infection to other people.

Unlike antibodies, which can tell if a person has ever had a virus or other pathogen, antigen tests can only identify the current infection. This is because the antigen disappears along with the pathogen with which it was associated when the infection clears.

Antibody test

An antibody test works differently from an antigen test in that it can be done after the antigens have left the body. This test is used to determine if an infection has ever occurred by secreting antibodies that were created when an immune response occurs.

Unlike COVID-19 antigen tests, antibody tests can be done after the infection is gone. When developing a vaccine, researchers will monitor whether the vaccinated person has developed antibodies.

Analysis of blood and tissue antigens.

Testing for various blood or tissue antigens is a very important aspect of a blood transfusion or a tissue or organ transplant.

In the case of a blood transfusion, the blood types must match the A, B, and O antigens of the donor and recipient. If the donor and recipient antigens do not match, it means that they have antibodies in their bodies that can immediately attack the incompatible donor red blood cells. The resulting transfusion reaction can be fatal.

Similarly, tissue typing, eg, for human leukocyte antigen (HLA) , is typically performed prior to organ or tissue transplantation to avoid rejection of the organ or tissue.

Get the word of drug information

Antigens can often be mistaken for antibodies, but they occupy very different positions when it comes to protecting against pathogens that can lead to harmful infections in the body. The antigen acts as an antibody generator and is cleared (along with the infectious agent) by the body's immune system.

When it comes to immunity, antigens may not be the main attraction, but they play a critical role in disease prevention and treatment.

Related Articles
Foods to Avoid If You Have Dry Mouth From Radiation

Dry mouth (xerostomia) is a common side effect of radiation therapy for people undergoing treatment for head and neck cancer. Read more

Thyroid adenoma: Causes, Treatment, and Diagnosis

The thyroid is a small, butterfly-shaped gland in the front of your throat that produces hormones affecting a number of Read more

NSAIDs and You Thyroid Function

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most frequently taken over-the-counter medications. Due to their systemic or whole body effects, it's Read more

How Doctors Are Failing Thyroid Disease Patients

The thyroid disease community has continually mentioned the lack of support they experience and the difficulty they have navigating the Read more