Immune System
From DrugPedia: A Wikipedia for Drug discovery
The immune system is a network of cells, tissues, and organs that work together to defend the body against attacks by “foreign” invaders like bacteria, parasites, fungi and viruses. The human body provides an ideal environment for many microbes.
The immune system is amazingly complex. It can recognize and remember millions of different enemies, and it can produce secretions (release of fluids) and cells to match up with and wipe out nearly all of them.
An antigen is any substance that elicits an immune response, from a virus to a sliver.
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[edit] Self and Nonself
The key to a healthy immune system is its remarkable ability to distinguish between the body’s own cells, recognized as “self,” and foreign cells, or “nonself.” The body’s immune defenses normally coexist peacefully with cells that carry distinctive “self” marker molecules. But when immune defenders encounter foreign cells or organisms carrying markers that say “nonself,” they quickly launch an attack.
[edit] Types of Immunity
Immunity can be either
- natural or artificial
- innate or acquired\adaptive
- active or passive
Active natural (contact with infection): develops slowly, is long term, and antigen specific.
Active artificial (immunization): develops slowly, lasts for several years, and is specific to the antigen for which the immunization was given.
Passive natural (transplacental = mother to child): develops immediately, is temporary, and affects all antigens to which the mother has immunity.
Passive artificial (injection of gamma globulin): develops immediately, is temporary, and affects all antigens to which the donor has immunity.
[edit] Major components of the immune system
- Thymus
- Spleen
- Lymph system
- Bone marrow
- White blood cells
- Antibodies
- Complement system
- Hormones
[edit] Major Cells of Immune System
The cells that are part of this defense system are white blood cells, or leukocytes. They come in two basic types which combine to seek out and destroy the organisms or substances that cause disease.
There are two kinds of lymphocytes:
* B lymphocytes * 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.
[edit] T Cells
T cells come in two different types, helper cells and killer cells. They are named T cells after the thymus, an organ situated under the breastbone. T cells are produced in the bone marrow and later move to the thymus where they mature.
[edit] Helper T-Cells
Helper T cells are the major driving force and the main regulators of the immune defense. Their primary task is to activate B cells and killer T cells. However, the helper T cells themselves must be activated. This happens when a macrophage or dendritic cell, which has eaten an invader, travels to the nearest lymph node to present information about the captured pathogen. The phagocyte displays an antigen fragment from the invader on its own surface, a process called antigen presentation. When the receptor of a helper T cell recognizes the antigen, the T cell is activated. Once activated, helper T cells start to divide and to produce proteins that activate B and T cells as well as other immune cells.
[edit] Killer T- Cells
The killer T cell is specialized in attacking cells of the body infected by viruses and sometimes also by bacteria. It can also attack cancer cells. The killer T cell has receptors that are used to search each cell that it meets. If a cell is infected, it is swiftly killed. Infected cells are recognized because tiny traces of the intruder, antigen, can be found on their surface.
[edit] B Cells
The B lymphocyte cell searches for antigen matching its receptors. If it finds such antigen it connects to it, and inside the B cell a triggering signal is set off. The B cell now needs proteins produced by helper T cells to become fully activated. When this happens, the B cell starts to divide to produce clones of itself. During this process, two new cell types are created, plasma cells and B memory cells.
[edit] Plasma Cell
The plasma cell is specialized in producing a specific protein, called an antibody, that will respond to the same antigen that matched the B cell receptor. Antibodies are released from the plasma cell so that they can seek out intruders and help destroy them. Plasma cells produce antibodies at an amazing rate and can release tens of thousands of antibodies per second.
When the Y-shaped antibody finds a matching antigen, it attaches to it. The attached antibodies serve as an appetizing coating for eater cells such as the macrophage. Antibodies also neutralize toxins and incapacitate viruses, preventing them from infecting new cells. Each branch of the Y-shaped antibody can bind to a different antigen, so while one branch binds to an antigen on one cell, the other branch could bind to another cell - in this way pathogens are gathered into larger groups that are easier for phagocyte cells to devour. Bacteria and other pathogens covered with antibodies are also more likely to be attacked by the proteins from the complement system.
[edit] Memory Cells
The Memory Cells are the second cell type produced by the division of B cells. These cells have a prolonged life span and can thereby "remember" specific intruders. T cells can also produce memory cells with an even longer life span than B memory cells. The second time an intruder tries to invade the body, B and T memory cells help the immune system to activate much faster. The invaders are wiped out before the infected human feels any symptoms. The body has achieved immunity against the invader.
