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How does the immune system work

The best way to understand the immune response to an invader, be it, a virus, bacterium or any other outside agency, is to imagine a war being fought at microscopic levels in our bodies. Based on this metaphor we can think of the immune system as an "army" to defend a country from an attack or invasion from outside. Just like the soldiers do when their country is attacked, the immune system responds to any attack control organism. The immune system is composed of a complex system of soluble protein and white blood cells (cells) that work together to respond to attacks, limiting damage and diseases caused by invading organisms.

immune system works with other systems

White blood cells (produced within the bone marrow) from three "regiments" different: the phagocytes (including macrophages) and two types of lymphocytes, T cells and B cells. The phagocytes are part of a defense mechanism-specific T and B cells and selectively target and represent the body's specific defense mechanism. The elements of the immune system are divided into two main categories: humoral immunity and cell-mediated immunity. The humoral immunity refers to antibody production by B cells (see below details). The cell-mediated immunity refers to T cells, and in particular, the CD8 cells. This terminology is particularly important for the science of vaccines, because vaccines can induce different, more or less effective, each of the two responses.

The humoral responses are able effectively block the particles of a virus (or other agents) before the intruder managed to enter the cell: it configures itself as a first line of defense and effective.
However, once the virus can infect the cell; cellular immunity has become crucial to the battle each category has its own function, and its defense strategy, but both the one or the other have the alike goal: to identify and destroy invading agents and / or bodies, which may be harmful to our bodies, creating an 'immunological memory' of these agents, to ensure that, where the same agents present themselves again, the body can respond immediately to the invasion.

Within each stage there are several immune response:

First phase: the battle begins;
Second phase: the forces are multiplied;
Third stage: attack and victory against the invader;
Fourth phase: end of hostilities.

Organs of the immune system

The organs of the immune system organs are divided into primary and secondary:

The primary organs [thymus and bone marrow] are the site of origin of the cells of the immune system in the first organs those are the precursors of T and B cells. These are cells whose DNA is still in
germline configuration and within which have not yet taken place rearrangements of immunoglobulin genes or T-cell receptor;
The secondary organs include the lymph nodes, spleen, appendix, plates
of Waldeyer's ring and Peyer (in other words, tonsils, adenoids, and palatine lymphatic tissue).

First phase: the battle begins

The phagocytes (which we consider as "spies" of the immune system) constantly patrol throughout the body (the blood stream, tissues, and the lymphatic system). Their goal is to identify every substance, every object and every foreign body (and potentially dangerous to the body). Phagocytes are also called the "scavengers" of the immune system. When the phagocytes identify an enemy, try to incorporate them immediately and destroy it.

While phagocytes are generally capable of destroying chemicals, poisons, and pollutants such as dust, smoke, or particles of asbestos, however, fail to destroy organic invaders such as viruses, bacteria, fungi, and protozoa.

For this reason, on encountering an invader organic (such as an influenza viruses), phagocytes, or emit chemical signal molecules that activate macrophages, phagocytes special to help the phagocytes in the attack the intruder.

A distinctive feature of macrophages is to mobilize specialized elements of the immune system to respond selectively to specific viruses. This is the defense system which includes lymphocytes (T cells and B). To ensure that mobilize lymphocytes, macrophages engulf the virus and have some "pieces" of the virus on its surface. This process is called "antigen presentation." The piece of viruses "developed" on the surface of the macrophage functions as a "red flag" that informs the T cells that an invader has entered the body, thereby activating the immune response. The T cells get their name from the thymus, an organ that is located at the base of the neck. The thymus generates a lot of T cells, each capable of recognizing a different type of antigen (an antigen is a substance that is detected and recognized by a component of the immune system, for example, antibodies or cells). The type of antigen that the T cell can recognize is determined by the receptors located on the surface of T cells. The surface of each T cell has many receptors. We can imagine a door with many locks and each lock for one specific type of key. The keys are the antigens on the surface of macrophages. There are tens of millions of antigens. Our immune system can create T cells capable of recognizing the most part, by activating an immune response strong and durable.

Depending on the receptors on the surface of the macrophage, a T cell can distinguish the hepatitis virus from that of 'flu, without ever having seen before. T cells that belong to this category are called "naive T cells." Naive T cells are the fresh troops, the virgin field of battle, called to intervene when we get sick, we contract an invigorated disease or a new infection. There are even T cells can recognize antigens produced in an artificial laboratory that the human body has never encountered in millions of years of evolution. The type of T cell that recognizes the antigen is called the CD4 cell (also called CD4 helper T-cell or lymphocyte), one of the same names situated on its surface called receptors, in fact, CD4 receptor. Although not usually the cells that kill the invader, CD4 cells are the most important of the entire immune system. This is because their main function is to send signals that direct and mobilize other "troops" into battle. We should think of T-helper cells as troop commanders or generals of the armies raised in defense of our body. CD4 cells and macrophages and then put together their forces, beginning the second phase of the war. The role of CD4 cells in the body's immune response CD4 cells play a crucial role with respect to the body's immune response. CD4 cells protect the body of the invasion of certain bacteria, viruses, fungi and parasites, and are able to destroy some cancer cells. The CD4 performed many functions, one of which is orchestrating the secretion of a variety of substances, including chemical messengers (such as interferons and interleukin), necessary for the defense of our body; CD4 cells also influence the development and functionality of macrophages and monocytes. Opportunistic infections can get the better of the organism only if the number of CD4 cells is reduced dramatically (below).

Second phase: The forces are multiplied

Once they have received information regarding the new invader by macrophages, CD4 began to divide and send signals to other components of the defense system to ensure that the system become as effective as possible. The additional forces include B cells (so-called called because they were produced by the bone marrow, in English "bone marrow") and T lymphocytes "killer," a special type of T cells, CD8 also called by the name of a receptor found on the surface. B cells and CD8 cells are involved in the response to the attack of foreign invaders. B cells (the "Third Regiment") are found in lymph nodes, and are part of the humoral immune system. As with T cells, B cells respond unlike to different antigens. When an invader is recognized as such by a B cell, the B cell starts to divide to prepare for battle. At a time when B cells reach maturity, they can become plasma B cells, substances capable of producing antibodies that can surround and immobilize a virus or bacterium that moves freely in the blood, and that has not yet invaded a cell. When the virus disappears from the blood, the cells die out, leaving the field free for the future battlefield. However, a second type of B-cells, called "B-cell memory," will not die, and instead remain in the bloodstream ready to respond more quickly to any external attack. Plasma B cells produce antibodies that make unarmed invading organisms. External agents are generally neutralized by adhering to their surface (thus preventing the invader's ability to carry out its offensive action). The memory cells remember an invader-specific, and remain present in both blood and lymphatic system.

Third phase: The attack and victory

One of the ways in which viruses and bacteria use to invade our bodies, our cells use to their advantage. In this way, cells become "factories" of viruses and bacteria. Responding to the orders of T helper cells, killer T cells destroy infected cells chemically piercing the membrane and ensuring that content is lost. This 'leakage' stops the replication cycle of the virus. Once the content of an infected cell is lost, the antibodies neutralize the virus attaching itself to the viral surface. This process prevents the virus from invading other cells. The action of the immune system slows the progression of invading organism and causes it to become easy prey to the phagocytes or macrophages involved "cleaning up." The antibodies also produce chemical reactions that can kill infected cells. When all the invaders are destroyed, the war is won, and the troops are finally recalled.

Phase Four: the end of hostilities

Once invaders have been eliminated, and a third type of T cells takes over: suppressor T cells or "peacemaker" release a substance that blocks the production of antibodies by B cells. These specific T cells to killer T-cells also ordered to stop the attack and the CD4 cells to terminate their management function. In this case, many T cells disappear soon after the battle, but some memory T cells remain in the bloodstream and lymphatic system, and will be able to respond faster if the alike type of virus occurred again. At this point, the war is won and the person - for the future - is ready to face another attack by the same virus.

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