Immune system

The immune system of a organization is a coordinated whole of elements which makes it possible to discriminate it “to oneself” “not-oneself”. It acts like a mechanism of defense against the Pathogène S, such as the Virus, the Bactérie S, the parasite S, the cancer cells, certain particles or “foreign” Molécule S (of which some Poison S).
Il is responsible for the phenomenon of rejection of Clerc's Office.
On counts several alternatives of immune systems among the animal species, and sometimes same a organization can accommodate several immune systems (the human Cerveau, for example, has its own immune system, distinct from that of the remainder of the body). Many species, whose Mammalian S, use the alternative described hereafter.

The word “immunity” comes from Latin immunitas ( “exempted of load” )

The principal agents of the immune system are the immunizing cell S called Leucocyte S (or white globules ) produced by original cells, within the osseous Moelle.

There exist two types of mechanisms of defense:

not-specific or innate or natural mechanisms of defense, like the protection of the skin and the mucous membranes, the gastric acidity, the phagocytic cells or the tears;
specific mechanisms of defense, like the directed action of the Lymphocyte S and production of specific antibodies.

One calls immunizing response the activation of the mechanisms of the immune system vis-a-vis an aggression of the organization.
l' together of these systems (including at the man vaccination) allows the immunizing impact strength ; concept which recovers the sum of the effective mechanisms of defense of an organization with respect to an disease-causing agent (of the Greek pathos : misfortune).

Mechanisms of defense

The organization defends itself against the aggressions, i.e. processes which result in to destroy living beings. These aggressions can take various forms:

aggressions known as physicochemical:
* Mechanical: climatic frictions, shocks, falls, etc
* Factors: altitude, abrupt change of temperature, radiations, dryness, dust, etc
* Aggression by chemical agents: acids, bases, etc

aggressions by other living beings:
: An organization indeed constitutes for another organization an ideal place for its own cells and also for a certain number of micro-organisms which could proliferate there, it is then about a Infection. The attackers in this case can be:
*des Virus
*des bacteria
*des mushrooms
*des Yeast S
*des Helminth S
*des Arthropod S

Not-specific mechanisms of defense

Physical barriers

the Peau is the largest first, and the most important element of the immune system: he prevents the entry of the majority of the foreign body. The people who lose too much skin, by Brûlure for example, succumb to infections. To avoid that, they are placed in maintained hospital rooms Stérile S.
the Muqueuse S which recover the ways oropharingiennes and digestive, the tracts respiratory and urogenital also constitute a physical barrier. The cells very narrowly juxtaposed are impermeable with the majority of the infectious agents. On the surface of certain mucous membranes, a film of Mucus animated by the beats of cilia makes it possible to fix, coat then to evacuate towards the outside the majority of the particles or to be alive intruders.
the cells have finally various chemical and biochemical “passive” systems of defense (enzymes, fatty-acids, lactic acid, intestinal Flora, pH of the body…).

Phagocytic cells

The phagocytic lymphocytes (which capture then digest the microbes) are with:

70% of the granulocytes neutrophiles,
5% of the Monocyte S, which will be transformed thereafter into Macrophage S,
1,5% of the eosinophilic granulocytes.

System of the complement

The system of the complement is a whole of proteins belonging to not-specific immunity and acting by a proteolytic cascade.

The angular stone of this system is the C3b protein. It allows:

of opsoniser bacteria, and to thus allow the fixing of the macrophages their surfaces;
to recruit the complex CAMWOOD (complex of attack of the membrane of the bacteria).

One arrives at the C3b protein of the complement in 3 different ways:

by the way known as " classique" : the cascade is started by the connection of the antibody (related to the antigen) with first protein of the C1 complement;
by the connection of a protein specific to a sugar being on the surface of the bacterium;
by the connection of the factor B in C3b already inserted in the bacterial membrane. It is what is called the alternative way.

Inflammatory reaction

The 4 signs of the ignition are: redness, heat, pain and puffiness.

inflammatory reaction:
vascular *réaction
cellular *réaction

the Phagocyte S and lymphocytes T cytotoxic:
* phagocytic leucocytes
* the cytotoxic lymphocytes T

antimicrobic proteins (defense humorale).

Lymphatic system

The white globules pass the major part of their time out of the circulatory system, and patrol in the interstitial liquid of the cells where proceed the majority of the fights against the disease-causing agents. Certain macrophages reside permanently in the bodies (lungs, liver) or in the lymphatic system.

Lymphatic system: it includes/understands various bodies (Thymus, osseous Moelle, Rate, amygdalae, Appendice and ganglia lymphatic) which play a big role in the immune system.

The lymphatic capillaries absorb part of the interstitial liquid which bathes fabrics. The liquid, then called lymph, ends up turning over in blood circulation via the thoracic channel. On its course, the lymph crosses many lymphatic ganglia in which any disease-causing agent meets white globules.

Specific mechanisms of defense

Specificity
Recognition of self and not-oneself:
* oneself:
*: Self of an individual is defined by receivers on the membrane of its cells, these receivers constitute markers of his identity (indentity card). In the case of the Lymphocytes NK, it is the absence of molecule of self which starts the answer.
* not-oneself:
*: Not-oneself of an individual is defined by receivers cellular or any other molecule different from self and thus recognized like foreigners by our organization. Not-oneself starts an immune reaction.

Immune system humoral

The immune system humoral acts against the bacteria and the viruses in the liquids of the human body (such as the Sang - historically blood and the lymph were named the moods body). Its principal means of action are the Immunoglobuline S, so called Anticorps , produced by the cells B ( B because the cells B were discovered in the bird in the " Stock Exchange of Fabricius" ; thereafter the " B" was preserved because Bone marrow , osseous marrow in English corresponds instead of maturation of these cells).

Cellular immune system

The cellular immune system deals with the cells infected by viruses, bacteria, and the cancer cells. The action is carried out via the cells T, so called lymphocytes T ( T because these cells mature in the thymus after their birth in osseous marrow). One distinguishes two big families from cells T:

the cytotoxic cells T (T_C) recognize the cells infected by using receivers to test the surface of the other cells. If they recognize an infected cell, they can destroy it as well as the virus which it contains.
the cells T Helper (T_H) which interact with the Macrophage S (which introduce dangerous substances) and also produce Cytokine S (Interleukine) inducing the proliferation of the cells B and T .

To the lymphocytes T are added also cells known as “NK” for Natural Killers. These cells are implied in an answer halfway between specific and nonspecific, according to the situations. They play in particular a part at the beginning of pregnancy, the fetus having to protect itself from them to be able to survive in the belly of his/her mother.

Diseases of the immune system

The immune system can pose problems either in excess or at fault:

Indeed if the immune system attacks the cells of the organization which are not pathological (by bad recognition), it then will create a auto-immune Maladie which will be characterized by a continuous ignition of certain fabrics or by necroses complete certain fabrics (for example diabetes of the type I).

If there is a defect of the immune system, in this case the pathogenic ones or cancers will be able to develop more easily.

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