Your white blood cell, the lymphocyte, is

Your immune system uses antigens to identify which cells belong to you and which should be destroyed. In this lesson, learn about nonself-antigens, self-antigens, and allergens, and how your immune system responds to them.

Who Are You?

What makes you the unique person you are? Is it your great personality, the color of your eyes, or maybe the sound of your voice? While all of these are important, at a cellular level, it’s actually your antigens.

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Every cell in your body has markers that identify it as being uniquely YOU. Microorganisms like bacteria and viruses have their own unique markers as well, and your immune system looks for the presence of these markers to know when to attack. These markers, called antigens, are most often small proteins, but can also sometimes be fragments of nucleic acids, carbohydrates, or even fats.The antigens on your own cells are known as self-antigens, while those that do not originate in your body are called non-self antigens.

Self-antigens are present on all your cells, but they’re particularly important in blood cells. You can only receive a blood transfusion from a donor with the same type of antigen. Otherwise your immune system will attack the donated blood because it will display antigens that are not recognized as being self-antigens.Non-self antigens are present on bacteria and viruses such as influenza and tetanus, which invade your body and make you sick. They are also present in blood or organs transplanted from another person who has antigens different from yours.If any non-self antigens are found inside your body, your immune system immediately goes to work trying to eradicate them. This is great when you’re sick and need to kill viruses and bacteria, but the system is very sensitive, and there are many ways in which it can go wrong.

Non-Self Antigens

One type of white blood cell, the lymphocyte, is responsible for recognizing and reacting to non-self antigens. As lymphocytes grow and mature in your bone marrow and then thymus, they’re exposed to your own antigens so they learn not to react to them. Once lymphocytes mature and are released into your body, they are always on the lookout for antigens they don’t recognize as being a part of you. There are two types of lymphocytes, T-cells and B-cells; these work together to initiate an antibody response.If a B-cell encounters a non-self antigen, it binds to it. With the help of a T-cell, the B-cell will become fully activated, and it will then start dividing to produce large plasma cells that release antibodies targeting the alien antigen. Each antibody has an antigen-binding site that will only attach to one specific type of antigen.

When antibodies bind to antigens, it helps other parts of the immune system to locate and destroy invading microorganisms.In addition to antibody-producing plasma cells, memory B-cells are also produced during an immune response. These can stay in your body for many years, and the presence of these memory B-cells means that if you’re exposed to the same antigen again, antibody production starts much more quickly. This is the basis of vaccines.

A vaccine contains pieces of a virus or bacteria that will trigger the production of antibodies and memory B-cells. Then your immune system will recognize the infectious agent, ready to immediately destroy it if you ever encounter it again.

Allergies and Autoimmune Diseases

Although antigen recognition and antibody production is a critical part of your immune system, in some people, the immune system overreacts and produces antibodies to self-antigens or to things that aren’t really dangerous, like pollen or peanuts.Autoimmune diseases such as lupus and rheumatoid arthritis occur when antibodies are produced that target your self-antigens. This causes some of your own cells and tissues to be destroyed and can cause many health problems.

Antigen recognition also plays a role in allergic reactions. Some molecules that enter your body are similar to the antigens on microorganisms that might invade your body. In some people, the immune system cannot tell the difference between these allergens and a dangerous germ. Allergens cause an immune response when none is necessary; this is what we call an allergic reaction.

Examples of allergens include pollen and dust.

Antibodies and Transplantation

Another situation in which antigen recognition is very important is in transplantation. If you receive a blood transfusion, you probably know that you have to be careful that the donor blood matches your blood type. If the donated blood has antigens different from your own, then your immune system will attack it, causing blood clots to form.

This situation can be even more serious if you receive an organ transplant. Before performing a transplant, doctors try to find a donor organ that has antigens that are as similar to the patient’s as possible, but people who have received organ transplants have to take immune suppressant drugs for the rest of their lives to prevent the new organ from being destroyed by antibodies that recognize the non-self antigens.

Lesson Summary

Antigens are small proteins that are embedded in the membranes of all the cells in your body. The antigens on your own cells are known as self-antigens, while those that do not originate in your body are called non-self antigens. Immune cells called lymphocytes recognize non-self antigens and produce antibodies that bind specifically to each antigen.

This helps the immune system to recognize and destroy invading microorganisms. Sometimes, antibodies to self-antigens can be produced by your immune system, and this leads to the development of autoimmune diseases. In other cases, antibodies are produced to allergens in your environment like pollen, and this causes an allergic reaction.

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