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Immune Systems And Disorders
When your body encounters a germ, its first line of defense is your immune system. Specialized cells and organs help your body recognize and respond to foreign invaders. Your immune system even has its own circulatory system, called the lymphatic system.
If your immune system cannot do its job, the results can be serious. Disorders of the immune system include
- Allergy and asthma - inappropriate immune responses to substances that are usually harmless
- Graft-vs.-host disease - a life-threatening reaction in people receiving organ transplants
- Immune deficiency diseases - disorders in which your resistance to disease becomes dangerously low
- Autoimmune diseases - diseases causing your immune system to attack your own body's cells and tissues by mistake
The cells that are part of this defense system are white blood cells, or leukocytes (pronounced: loo-kuh-sytes). They come in two basic types (more on these below), which combine to seek out and destroy the organisms or substances that cause disease.
Leukocytes are produced or stored in many locations throughout the body, including the thymus, spleen, and bone marrow. For this reason, they are called the lymphoid (pronounced: lim-foyd) organs. There are also clumps of lymphoid tissue throughout the body, primarily in the form of lymph nodes, that house the leukocytes.
The leukocytes circulate through the body between the organs and nodes by means of the lymphatic (pronounced: lim-fah-tik) vessels. (You can think of the lymphatic vessels as a type of highway between the rest stops that are the lymphoid organs and lymph nodes). Leukocytes can also circulate through the blood vessels. In this way, the immune system works in a coordinated manner to monitor the body for substances that might cause problems.
There are two basic types of leukocytes:
- The phagocytes (pronounced: fah-guh-sytes) are cells that chew up invading organisms.
- The lymphocytes (pronounced: lim-fuh-sytes) are cells that allow the body to remember and recognize previous invaders.
There are two kinds of lymphocytes:
The B lymphocytes and the T lymphocytes. Lymphocytes start out in the bone marrow and either stay there and mature into B cells, or they leave for the thymus gland, where they mature into T cells. B lymphocytes and T lymphocytes have separate jobs to do: B lymphocytes are like the body's military intelligence system, seeking out their targets and sending defenses to lock onto them. T cells are like the soldiers, destroying the invaders that the intelligence system has identified.
Here's how it works.
A foreign substance that invades the body is called an antigen (pronounced: an-tih-jun). When an antigen is detected, several types of cells work together to recognize and respond to it. These cells trigger the B lymphocytes to produce antibodies. Antibodies are specialized proteins that lock onto specific antigens. Antibodies and antigens fit together like a key and a lock.
Once the B lymphocytes have produced antibodies, these antibodies continue to exist in a person's body. That means if the same antigen is presented to the immune system again, the antibodies are already there to do their job. That's why if someone gets sick with a certain disease, like chickenpox, that person typically doesn't get sick from it again. This is also why we use immunizations to prevent getting certain diseases. The immunization introduces the body to the antigen in a way that doesn't make a person sick, but it does allow the body to produce antibodies that will then protect that person from future attack by the germ or substance that produces that particular disease.
Although antibodies can recognize an antigen and lock onto it, they are not capable of destroying it without help. That is the job of the T cells. The T cells are part of the system that destroys antigens that have been tagged by antibodies or cells that have been infected or somehow changed. (There are actually T cells that are called "killer cells"). T cells are also involved in helping signal other cells (like phagocytes) to do their jobs. Antibodies can also neutralize toxins (poisonous or damaging substances) produced by different organisms. Lastly, antibodies can activate a group of proteins called complement that are also part of the immune system. Complement assists in killing bacteria, viruses, or infected cells. All of these specialized cells and parts of the immune system offer the body protection against disease. This protection is called immunity.
Information obtained from National Institute of Health