Antigen: Meaning & Explanation

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  • 0:02 Antigens
  • 0:33 Antigens and the Immune System
  • 1:59 Antigens and Antibodies
  • 2:40 Blood Type Antigens
  • 3:42 Lesson Summary
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Lesson Transcript
Instructor: Kelly Robson

Kelly has taught High School Science and Applied Communications. She holds an Education Specialist Degree in Ed. Leadership.

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. 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.

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