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Antigens are invaders that sneak into our bodies and can possibly cause us harm; however, they trigger our immune system, which fights them off. This lesson explains antigens and some of the processes that go along with them.


Antigens are the little invaders that enter the body and trigger the immune system. They come in all different shapes and sizes.

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Antigens are mainly microbes such as bacteria, parasites, and fungi. They can also come from the environment, such as viruses, chemicals, pollen, and more. Each antigen may cause infection to the body.

There are some antigens that seem harmless but still cause the immune system to respond, like pollen for example. These are called allergens.

Antigens and the Immune System

When antigens enter the body, the immune system alarm is triggered. The first line of defense is for the B-lymphocytes, or B cells, to be sent out. These are special leukocytes, also called white blood cells. Their job is to tag the antigen so that the correct response can be made.

B cells hang out in bone marrow waiting for antigens to enter the body. When an antigen like bacteria enters the body, the B cells will leave the bone marrow and seek out the bacteria antigen. The B cells recognize if the antigens belong to the body or if it is an intruder.When the B cells tag the intruding antigen, it will also create special proteins, antibodies that lock onto the antigen. This also sends chemical signals to the rest of the immune system. After the B cell finishes its job, the T cells take over and begin to destroy the antigen. T cells may need help from the cleanup crew, phagocytes.

Phagocytes are another type of white blood cell. Their job is to chew up and eliminate the antigen all together.Since the antigen was bacteria, the phagocyte that was released was probably neutrophil. Neutrophils are the most common of the many different types of phagocytes.

It is made to destroy bacteria. If a doctor draws blood and sees a raised level of neutrophils, the doctor can determine that the patient probably has a bacterial infection.

Antigens and Antibodies

Once an antibody is created, it will stay in the body and wait for the next invader that it was made for. For instance, if a patient was invaded by the Chicken Pox virus antigen, then the patient would remake the antibodies necessary to fight it off. Now, those Chicken Pox destroying antibodies wait around in the body, ready to fight off the virus as soon as it enters.This is also how vaccines protect us from antigens.

Vaccines contain just enough of the antigen to send the immune system into action. The immune system will tag the antigen and create the antibodies. These antibodies will destroy the antigen. Then they wait around in case the antigen wants to try to attack again.

Blood Type Antigens

Blood cells contain antigens attached to the outside membrane of the cell. These antigens create specific antibodies that will take specific blood types. For example, blood type A has antigens that create antibodies that will destroy blood type B. Therefore, if you give a person with A blood type any B blood, the antibodies will destroy it, and vice versa.To make it a little trickier, there is also AB blood.

AB blood does not make any antibodies, so it welcomes any type of blood. It is considered a universal receiver; however, someone with AB blood can only donate blood to others who have AB blood. Blood type O is the reverse of AB. O makes antibodies against both A and B blood types. Therefore, people with O blood type can only receive O blood. Since there are no antibodies that attack O blood, one with O blood is considered to be a universal donor. Everybody can receive O blood.

Lesson Summary

Antigens are invaders that spring our immune system into action. Our immune system knows how to take care of these little buggers; however, these antigens can cause infections. Once an antigen is detected and tagged by a B cell, an antibody is made. These antibodies stick around and wait to protect the body should the antigen decide to return.

Blood antigens give us our blood codes and make donating blood and receiving blood a somewhat complicated process.


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