Bio Quiz
The immune system is the body's defense system. It protects the body from potentially harmful substances by locating and responding to antigens. Antigens can be proteins and/or located on the surface of cells, fungi, viruses, and bacteria, or other substances such as toxins, chemicals, drugs, and foreign particles (such as a splinter). The immune system sends out antibodies to destroy antigens, but leaving beneficial and friendly antigens alone.
http://www.nlm.nih.gov/medlineplus/ency/article/000821.html
(This picture illustrates antibodies attacking antigens as discussed above)
Picture from: http://www2.estrellamountain.edu/faculty/farabee/biobk/biobookimmun.html
1- An innate, or nonspecific immune response is an immediate response to any foreign antigens. Everyone is born with innate immunity, which is made up of barriers and is the first line of defense of the immune system. Examples of innate immunity include: Cough reflex, enzymes in tears and skin oils, mucus, which traps bacteria and small particles, skin, and stomach acid.
How does it do what it does?
If pathogens (disease-causing cells that carry antigens) are to make it past the physical barriers of the skin, they are met by complement proteins, phagocytes, and natural killer cells.
Complement Proteins
The liver produces around 20 complement proteins that work together to destroy antigens. They do this either by marking them for ingestion by other immune cells, sending out chemical signals to bring additional immune cells to join the fight, or combining together with one another and killing the invaders directly by punching holes them.
(This diagram shows complementary proteins sending signals to other complementary proteins (complement cascade) which then assist in the eventual cell burst)
http://www.niaid.nih.gov/topics/immunesystem/immunecells/Pages/complementSystem.aspx
Phagocytes
Phagocytes are white blood cells which ingest harmful foreign particles, bacteria, and dead or dying cells. Phagocytes are divided into two classes: professional, and nonprofessional. Professional phagocytes are primarily concerned with ingesting pathogens. They have special receptors embedded on them that allow them to detect foreign objects not normally found in the body. Professional phagocytes include dendritic cells, macrophages, mast cells, monocytes, and neutrophils. Nonprofessional phagocytes do sometimes ingest pathogens, but that is not their main job. Examples include: epithelial cells, endothelial cells, fibroblasts, and mesenchymal cells. For instance, fibroblasts are concerned with remolding scars, and in the process, they sometimes ingest foreign particles.
(This illustration shows a macrophage (phagocyte) using its embedded receptor to communicate with an antigen to determine if its friend or foe. It is foe because the macrophage has called upon a antibody to assist it)
http://en.wikipedia.org/wiki/Phagocyte
Killer cells
Natural killer cells are lymphocytes (type of white blood cell) which attack tumors and body cells infected by viruses. NK cells wait in the blood stream, and in the liver and spleen which store blood, until they are needed at the site of an infection. They give off a chemical (ctyokine) which alerts nearby phagocytes for backup. They also evaluate body cells to determine whether they have been infected by a virus. Once they find infected cells, they inject those cells with enzymes that cause the body cells to self-destruct, or they signal the cell to commit suicide, destroying the pathogens.
For the entire innate response section: http://www.novimmune.com/science/innate.html
2- T cells are lymphocytes. There are many different types of T cells, but the most important are Helper and Killer T Cells.
Helper T cell activation
Helper T cells, which carry information and decide when to give the green light to other immune cells to carry out an immune response, are activated to initiate immune reactions. This is how Helper T cells are activated: macrophages, a type of phagocyte, goes out and swallows foreign particles, but leaving behind some antigen. Helper T cells then go and read the antigen, and if it is harmful, the cells activate and signal the macrophage to finish off the antigen, then go activate other T cells and divide and produce special proteins which signal other immune cells to attack the antigen as well.
Killer T cell activation
Killer T cells are alike phagocytes except that instead of engulfing the entire pathogen, they inject enzymes which destroy the nucleus and structure of the invader. Killer T cells are activated by Helper T cells through the process described above.
This entire section is from: http://sepa.duq.edu/regmed/immune/tcells.html
B cells are lymphocytes responsible for creating antibodies. They remain in peripheral tissues until they encounter an antigen and are activated. They require 2 signals for activation: The first activation signal occurs upon antigen binding to B cell receptors (BCRs), and the second signal occurs via either a thymus-dependent or a thymus-independent mechanism. Thymus dependent means Helper T cells assist in activation, and thymus-independent means the B cells are activated directly by the antigen.
This section from: http://www.rndsystems.com/molecule_group.aspx?r=1&g=3175
http://en.wikipedia.org/wiki/B_cell
3- "The adaptive immune system plays three primary roles. First, because the response by the innate immune system is non-specific, if it goes on too long it can also damage healthy cells in the process. Second, because microbes like bacteria and viruses continually mutate, over time they become resistant to particular drugs as well as to the effects of the immune system. To counter that, the adaptive immune system, as the name implies, can adapt itself to target very specific mutations ofantigens as they are encountered. And third, the adaptive immune system protects us against reinfection."
The main components of the adaptive immune system are B cells and T cells (activation described above). These cells travel through the blood stream looking for antigens. "Once they encounter invaders, these B-cells and T-cells learn how to attack this one specific antigen. They then replicate in massive numbers in order to fight the invader. B-cells also create antibodies programmed to attach themselves to the particular antigen being encountered. These antibodies, in turn, can sometimes directly interfere with the functions of the antigens, they can mark the antigen for ingestion by white blood cells, or they can create a physical link between the antigen and other immune system cells allowing those immune cells to kill the antigens."
Unlike the innate response, the adaptive immune system gradually kills invaders. "However, after the foe is vanquished, some of the B-cells and T-cells remain in the body as memory cells so that the next time this particular threat is encountered, the adaptive immune system will recognize it immediately, and mount a much quicker and more efficient attack."
From: http://www.novimmune.com/science/immune.html
(This diagram shows the differences between an adaptive (gradual) and innate (immediate) system)
http://www.rikenresearch.riken.jp/eng/frontline/5028
4- Nearly every cell contains molecules that let the body know if it is self or nonself. Immune body cells normally do not attack cells with self markers. When these "troops" come across cells labeled as "foreigners," they move quickly to attack. These foreign particles are labeled by antigen markers.
The body will reject any proteins, no matter how beneficial, until they are broken down and their antigen markers disappear. An antigen announces its foreignness by means of intricate and characteristic shapes, called epitropes, which appear on its surface. Different shapes trigger different antibody responses.
Sometimes the body accidentally labels self cells as nonself, and triggers a misdirected attack. The result is an autoimmune disease.
(This picture depicts how antibodies examine markers to determine antigen or friend)
http://thyroid.about.com/library/immune/blimm02.htm
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