In most cases, the immune system does a great job of keeping people healthy and preventing infections. But sometimes problems with the immune system can lead to illness and infection. The immune system is the body's defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune system attacks organisms and substances that invade body systems and cause disease. The immune system is made up of a network of cells, tissues, and organs that work together to protect the body.
One of the important cells involved are white blood cells, also called leukocytes, which come in two basic types that combine to seek out and destroy disease-causing organisms or substances.
Leukocytes are produced or stored in many locations in the body, including the thymus, spleen, and bone marrow. For this reason, they're called the lymphoid organs. There are also clumps of lymphoid tissue throughout the body, primarily as lymph nodes, that house the leukocytes. The leukocytes circulate through the body between the organs and nodes via lymphatic vessels and blood vessels. In this way, the immune system works in a coordinated manner to monitor the body for germs or substances that might cause problems. A number of different cells are considered phagocytes.
If doctors are worried about a bacterial infection, they might order a blood test to see if a patient has an increased number of neutrophils triggered by the infection. Other types of phagocytes have their own jobs to make sure that the body responds appropriately to a specific type of invader. The two kinds of lymphocytes are B lymphocytes and 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 functions: B lymphocytes are like the body's military intelligence system, seeking out their targets and sending defenses to lock onto them.
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T cells are like the soldiers, destroying the invaders that the intelligence system has identified. These cells trigger the B lymphocytes to produce antibodies, which are specialized proteins that lock onto specific antigens. So if someone gets sick with a certain disease, like chickenpox, that person usually won't get sick from it again.
This is also how immunizations prevent certain diseases. An immunization introduces the body to an antigen in a way that doesn't make someone sick, but does allow the body to produce antibodies that will then protect the 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's the job of the T cells, which are part of the system that destroys antigens that have been tagged by antibodies or cells that have been infected or somehow changed. Some T cells are actually called "killer cells. Antibodies also can neutralize toxins poisonous or damaging substances produced by different organisms.
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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. Everyone is born with innate or natural immunity, a type of general protection. 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. Everyone is born with innate or natural immunity, a type of general protection. Many of the germs that affect other species don't harm us. For example, the viruses that cause leukemia in cats or distemper in dogs don't affect humans.
Innate immunity also includes the external barriers of the body, like the skin and mucous membranes like those that line the nose, throat, and gastrointestinal tract , which are the first line of defense in preventing diseases from entering the body.
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The second kind of protection is adaptive or active immunity, which develops throughout our lives. Adaptive immunity involves the lymphocytes and develops as people are exposed to diseases or immunized against diseases through vaccination. Passive immunity is "borrowed" from another source and it lasts for a short time.
For example, antibodies in a mother's breast milk give a baby temporary immunity to diseases the mother has been exposed to. This can help protect the baby against infection during the early years of childhood. Everyone's immune system is different. Some people never seem to get infections, whereas others seem to be sick all the time. As people get older, they usually become immune to more germs as the immune system comes into contact with more and more of them. That's why adults and teens tend to get fewer colds than kids — their bodies have learned to recognize and immediately attack many of the viruses that cause colds.
Immunodeficiencies happen when a part of the immune system is missing or not working properly. Immunodeficiencies also can be acquired through infection or produced by drugs these are sometimes called secondary immunodeficiencies.
The Human Complement System in Health and Disease
Immunodeficiencies can affect B lymphocytes, T lymphocytes, or phagocytes. Examples of primary immunodeficiencies that can affect kids and teens are:. Acquired or secondary immunodeficiencies usually develop after someone has a disease, although they can also be the result of malnutrition, burns, or other medical problems.
Certain medicines also can cause problems with the functioning of the immune system. In autoimmune disorders, the immune system mistakenly attacks the body's healthy organs and tissues as though they were foreign invaders. Autoimmune diseases include:. Allergic disorders happen when the immune system overreacts to exposure to antigens in the environment. The substances that provoke such attacks are called allergens. The immune response can cause symptoms such as swelling, watery eyes, and sneezing, and even a life-threatening reaction called anaphylaxis.
The Human Complement System in Health and Disease - CRC Press Book
Medicines called antihistamines can relieve most symptoms. Cancer happens when cells grow out of control. Leukemia , which involves abnormal overgrowth of leukocytes, is the most common childhood cancer.