Over the course of evolution, mankind has acquired a series of defensive mechanisms that make up the immune system, which by means of a specific and coordinated response to all foreign substances has the purpose of protecting the body from all those elements that can attack it.
The ultimate goal is to protect the body from infectious agents and / or foreign antigens
Immunity is not only anti-infectious but must be understood as the ability to maintain an identity and integrity and to maintain constant certain organic structures, to maintain a biological identity in practice.
IMMUNE SYSTEM: CHARACTERISTICS
The immune system is endowed with positive specificity: that is, the ability to recognize and react towards all that is foreign. But it is also endowed with negative specificity, that is, with the ability not to react towards all that is proper.
The foreign material is called antigen and defined as a foreign substance to the organism capable of evoking a humoral immune response, that is, with the formation of antibodies or tissue directly supported by cells called lymphocytes. An antigen introduced into the organism, causes the formation of antibodies (immunogenic) and is capable of reacting specifically with it.
TYPES OF IMMUNITY
Non-specific (or innate) immunity is already present before infections and has very rapid response time. Specific (or acquired) immunity is partially triggered by the previous one and with which it enhances the response; it is specific, that is, it is directed from time to time towards a specifically recognized foreign identity.
CHARACTERISTICS OF THE INNATE IMMUNE SYSTEM
It is always operational: its components are ready before the encounter with the microbe or are activated immediately after (a few hours) Recognizes various microbial components essential for the life of microorganisms and therefore cannot be eliminated by microbes in an attempt to escape the immune response Develop a response to microbes that is always identical It has no memory of contact.
WHAT ARE ITS COMPONENTS?
Skin and mucous membranes, neutrophilic granulocytes (50/75% of circulating GB), monocyte-macrophage system (bactericidal, antitumor action, etc.), dendritic and natural killer cells. Proteins: Defensins, lysozyme, lactoferrin, interferon, complement.
They are medullary derived cells and are distributed in almost all organs; they have receptors to recognize microbial-derived molecules. In response to their stimulation, they secrete cytokines and migrate to the lymph nodes where they act as antigen-presenting cells (APC) for T lymphocytes. They therefore represent the link between the innate immune system and the acquired immune system.
SPECIFIC IMMUNITY ACQUIRED
- Specificity ensures that the immune response to a microbe always faces that particular microbe
- Diversity (one billion Ag)
- Memory: T and B lymphocytes retain the memory of the former contact with the Ag, so as to respond more quickly and intensive to a new re-exposure
- Discrimination of self from non self
ORIGIN OF LYMPHOCYTES
All lymphocytes derive from bone marrow stem cells, but while T lymphocytes mature in the thymus, B lymphocytes mature in the same bone marrow. Once mature, all lymphocytes migrate to the peripheral lymphoid organs.
Structures of immunity
Pluripotent hematopoietic stem cells begin to appear in the fetal liver in the third month of pregnancy, then migrating to the bone marrow and thymus which constitute the primary lymphatic organs; here the cells continue to differentiate and proliferate.
Antibodies (gammaglobulins) They are produced by B lymphocytes and plasma cells in the secondary lymphoid organs but carry out their action everywhere. They have a Y shape and are made up of 2 heavy chains and 2 light chains; each chain is composed of a variable region that binds the antigen and a constant region that determines its class The classes are dominated by IgA, IgE, IgM, IgG, IgD.
Antibody response (Type 1)
- The organism after an initial exposure to a antigen, responds with the production of antibodies
- Usually, antibodies appear in the circulation about 10/15 days after the first contact to reach a peak after 2/3 weeks
- In the course of the primary answer also long survival memory B lymphocytes are generated.
Antibody response (Type 2)
- At the first contact with the antigen, the B lymphocyte only produces IgM that are eager to bind with Ag, but who are unable to activate phagocytosis. This leads to avoiding the early elimination of the Ag allowing longer contact with the immune system.
- Later, the individual cells pass from the production of IgM to that of faster IgG in activating the complement.
- At the end of the primary response some B lymphocytes they differ in memory cells.
SECOND EXPOSURE TO THE SAME ANTIGEN
A second exposure to the same antigen, months or years after the first, it causes a rapid appearance of IgG (1-3 days) they reach levels 10-15 times higher than those produced in the primary response (and also a improvement of the affinity of antibodies to antigen).
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