The immune system is the body’s tool for preventing or limiting infection. Without it, the body would be unable to withstand attacks from bacteria, viruses, parasites, and more.
The immune system consists of a vast network of cells, organs, proteins, and tissues throughout the body.
A fully functional immune system can distinguish healthy tissue from unwanted substances. If it detects an unwanted substance, it will mount an immune response — a complex attack to protect the body from invaders. It also recognizes and removes dead and faulty cells.
The immune system does not always get it right, however. Sometimes, for instance, it is unable to fight effectively because a person has a health condition or needs certain medications that affect how the system works.
In autoimmune diseases and allergies, the immune system mistakenly perceives healthy tissue as unhealthy and launches an unnecessary attack, leading to uncomfortable and sometimes dangerous symptoms.
This article will look at some of the main features of the immune system and how they defend the body from pathogens and other invaders. It will also look at problems that can arise with the immune system.
The immune system
The immune system consists of a range of components, including:
white blood cells (leukocytes)
the spleen
the bone marrow
the lymphatic system
the thymus
the tonsils, adenoids, and appendix
White blood cells circulate in the blood and lymphatic vessels.
The lymphatic system forms a network similar to the blood vessels. It carries a substance called lymph instead of blood. Lymph is a fluid that carriesTrusted Source immune-related cells to areas that need them.
White blood cells are constantly looking for pathogens. When they find one, they begin to multiply and send signals to other cell types to do the same.
The body stores white blood cells in different places, known as lymphoid organs.
These include:
The thymus: A gland behind the breastbone, where white blood cells known as lymphocytes mature.
The spleen: An organ at the upper left of the abdomen where immune cells gather and work.
Bone marrow: Soft tissue in the center of the bones that produces red and white blood cells.
Lymph nodes: These are small, bean-shaped glands throughout the body, especially in the neck, underarms, groin, and abdomen. They link via lymphatic vessels. Immune cells gather in lymph nodes and react when antigens are present. This can lead to swelling.
The tonsils, adenoids, and appendix: These are gateways for pathogens to enter the body, so lymphoid tissue is also there.
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