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Hey there, this time I'll teach you a little about an area that I have loved since I saw it when I studied the subject microbiology and clinical immunology: immunology. This part of medicine is extremely broad and in some ways complicated, but it is totally beautiful to know how to defend our body against any organism that tries to invade us. Next I'll give you an introduction to beautiful immunology.


###  What is immunity?


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It is a set of physiological mechanisms that allow us to recognize a substance as strange or harmful to offer resistance against it, either by neutralizing or destroying it, without injuring ourselves.

Immune system is responsible for we rarely having an infectious process despite the fact that we live in an environment full of pathogenic microorganisms, and when it occurs, thanks to it we develop an immune response to resolve the infection.

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[Source-Pixabay](https://pixabay.com/es/illustrations/defensa-protecci%C3%B3n-amenaza-1403072/)

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###  What are the functions of the immune system?


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Basically, defend our body against any infection, but it also acts when some kind of genetically different tissue is transplanted from that of the person receiving it; When there are neoplasms (own cells that transform and cease to be normal), for that reason, thanks to the immune system, those cells, despite being their own, can recognize them. So the main function is to protect our body from pathogenic organisms, for which it uses innate and acquired mechanisms.

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**Note:** 

*  Innate mechanisms is synonymous with: innate immunity, natural immunity, non-specific immunity, nonspecific immunity, or unlearned immunity.

*  Acquired mechanisms is synonymous with: acquired immunity, specific immunity, or learned immunity.

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##  Lines of immune defense:

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The immune system has 3 lines of defense; the first 2 are part of innate immunity, and the last is formed by acquired immunity. If the 1st line of defense fails to contain the pathogen, the 2nd line of innate immunity is activated. If the two 1st lines of defense failed to stop the microorganism, the 3rd line of acquired immunity is activated.

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##  Innate Immunity:


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Here the answer will always be the same regardless of the nature of the microorganism (virus, fungi, parasites), I mean, it is the ability to react widely against microorganisms or foreign substances.

This type of immunity is genetically determined, varies between species and even in individuals of the same species. This varies according to race, hormonal system, age and sex.

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The main feature of this immunity is that it doesn't require prior contact with the antigen, I mean, it doesn't matter if it is the first time or not that it contacts a microorganism because the response will be the same. So whether the response is effective or not, all microorganisms regardless of their characteristics have something in common, and are called "Pathogen-associated molecular pattern" (PAMPs), through which our body can know that something strange is found, through the called  "pattern recognition receptors" (PRRs)

Our body doesn't need to recognize the entire microorganism because they have lipopolysaccharides, peptidoglycan,lipoteichoic acid, bacterial DNA and glucan, which would be the equivalent to our organs and body parts and correspond to PAMPs.


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###  Normal microbial flora:

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Correspond to those microorganisms that are permanently in normal conditions in our skin, and they protect us from those external microorganisms that want to invade us. It consists of several mechanisms of action to defend ourselves such as for example modifying the pH of the place, or releasing peptides with antibiotic activity called colicins.

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[Source-Wikipedia](https://commons.wikimedia.org/wiki/File:Lactobacillus_sp_01.png)

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An example of the microbiota could be the Döderlein bacilli (_Lactobacillus_) found in the vagina which make the vaginal pH always acidic and therefore inhospitable for many external microorganisms.

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*  At the skin level, if it does'nt receive an injury that manages to undo its continuity, it is difficult for a person with an optimal immune status could enter a microorganism in his body. Also to the sweat glands that protect us through sweat (by dermicidin which is an antimicrobial peptide); The sebaceous glands also protect us by producing antimicrobial lipids for example.

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[Source-Pixabay](https://pixabay.com/es/illustrations/contra-la-gripe-fr%C3%ADo-enfermedad-1679104/)

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*  At the level of the airways are the turbinates, epiglottis, cough and sneeze mechanism (to expel whatever who wants to enter our body, they are the most important), the mucus (makes it difficult for the microorganism to enter), lysozyme (enzyme with bactericidal property found in tears, saliva, breast milk), lactoferrin (a protein with a lot of iron affinity, which acts as an antimicrobial and is found for example in the blood, semen, saliva) and other polysaccharides.

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*  At the level of the digestive system, a mucus is also found in the stomach that prevents invaders from attaching, and the same acidic pH of that site eliminates most microorganisms. In the small and large intestine there are millions of microorganisms (mostly anaerobes) that eliminate those that are pathogenic.

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[Source-Wikipedia](https://commons.wikimedia.org/wiki/File:Sistemaurinario.png)

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*  At the level of the urinary tract, the mechanism of urine ejection, the exit force of the urine prevents microorganisms from inhabiting, because said ejection works as a drag mechanism. The pH of the urine produces a hostile environment; Tamm Horsfall proteins prevent the adherence of microorganisms, and the narrow urethral sphincter prevents their entry.

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*  At the genital level, in man the seminal fluid has bactericidal action, and the pH is alkaline; In women as I mentioned above are the Döderlein bacilli that maintain the acidic pH in the vagina.

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###  Mechanisms  of innate immunity:

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*  Physical barriers.

*  Inflammatory mechanism.

*  Humoral mechanism: alternate pathway of the complement system.
*  Cellular mechanism: phagocytosis and activation of natural killer cells.



###  Inflammatory mechanism: 

Basically it is a mechanism whose main function is to save time for the cells responsible for destroying the pathogenic microorganism to arrive, this is achieved by “corralizing” it so that it does not expand further. This mechanism is activated when the tissues are injured, it is a quick response because the cells and substances that cause inflammation reach through the circulatory system.

So what is the purpose of inflammation?

Cordoning the microorganism so that it doesn't expand further, that is why this mechanism is very important.



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##  Acquired Immunity:


This one is perfected over the years as we are exposed to different types of microorganisms, this type of adaptation can be acquired whether or not suffering from diseases.

This type of immunity keeps a specific memory for any pathogen, that is, your response will vary depending on the microorganism you are going to face, so a person who was exposed to an antigen, his body will produce specific antibodies for that antigen not to another, for example: if I had rubella, it doesn't mean I can't give me measles because my body is prepared for rubella, not for measles.


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[Source-Wikipedia](https://commons.wikimedia.org/wiki/File:Antibody.svg)

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**Antigen:** it is a harmful foreign entity, but it can also be a part or some structure of that pathogenic microorganism, which upon entering our body produces an immunological response and therefore the production of antibodies.

**Antibody:** they are glycoproteins whose function is to identify and specifically combat the antigens that invade our body.


The defense mechanisms of acquired immunity are composed of 2 parts, the cellular part that are T and B lymphocytes; and the molecular part that are the antibodies or immunoglobulins.

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###  Acquired immunity uses 2 types of immunity: Active immunity and passive Immunity.

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**Active immunity:** It is one that is produced by previous contact with a microorganism, whether we have suffered an infectious process or not. This is further subdivided into:


-Natural active immunity: when we suffer the disease.

-Active artificial immunity: through vaccines which are injections containing antigens of a particular microorganism.

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[Source 1](https://pixabay.com/es/illustrations/fondo-hombre-enfermedad-creciendo-3037224/), [source 2](https://pixabay.com/es/photos/vacunaci%C3%B3n-impfspritze-m%C3%A9dica-2722937/)

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**Passive immunity:** this is acquired without having previous contact with the microorganism. It is also subdivided into:


-Natural passive immunity: through the placental barrier and breastfeeding, that is, when the mother gives her children her antibodies.

-Passive artificial immunity: for specific antibodies produced in other organisms, the so-called immune serum.


*  Immune serum: they are specific antibodies produced in other organisms, a good example of these would be the antiophic serum that are produced by inoculating the poison of these animals to a horse, then the horse produces antibodies to the poison and then the blood is extracted, It goes through various processes such as purification and the final result is a serum loaded with antibodies specific for the venom of that snake.

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[Source 1](https://pixabay.com/es/vectors/embri%C3%B3n-humana-infantil-embarazo-159690/), [source 2](https://pixabay.com/es/illustrations/lactancia-materna-madre-e-hijo-beb%C3%A9-2730855/), [source 3](https://pixabay.com/es/illustrations/jeringa-tiro-medicina-botella-1884758/), [source 4](https://pixabay.com/es/vectors/animales-equino-caballo-paseo-2029664/).

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###  Characteristics of adaptive immunity:

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*  Sensitivity: although microorganisms are very similar, this immunity manages to make minimal differences.

*  Diversity: although there are many microorganisms, it still has the ability to discern who has been in contact with and who has not.

*  Immunological memory: approximately 15 years, depending on the microorganism.

*  Specificity: it will act only with the one who activated it.

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##  Factors that determine the balance of the immune system:


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* Race: There are races more sensitive to certain pathologies than others that have generated immunity against certain diseases.

*  Gender: men are generally more vulnerable, but there are genders that may be disadvantaged when defending themselves against certain diseases.

*  Stress: the immune system is disturbed and its effectiveness decreases because of it.

*  Base disease: for example diabetes that conditions an alteration of the immune response which makes it easier for the person to contract a disease.

*  Climatic conditions: temperature variations can easily induce colonization or infection, for example in times of rain there is more diarrhea and flu.

*  Nutritional status: if the person has malnutrition, the body doesn't produce enough protein to intervene in the immune system like the collective.

*  Hygiene and habitat: where the individual lives and his lifestyle in general intervenes in a great way.

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Well dear readers I hope this publication is to your liking, any questions you have leave me in the comments¡, I hope you learned something new today.

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[Source-Wikipedia-CC BY-SA 3.0](https://commons.wikimedia.org/wiki/File:CD28_structure.gif)


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##  References:

*  Introduction to human immunology Fainboim-Geffner 5th edition, Pan American medical editorial.
*  Medical microbiology Murray-Rosenthal-Pfaller 7th edition, editorial Elsevier Saunders.
*  Basic Immunology: Functions and Disorders of the Immune System 5th Edition, Abul K. Abbas, Andrew H. H. Lichtman, Shiv Pillai.
* [The Immune System, Peter J. Delves, Ph.D., and Ivan M. Roitt, D.Sc. The New England Journal of Medicine.](https://www.nejm.org/doi/full/10.1056/nejm200007063430107)
* [Interactions Between the Microbiota and the Immune System, Lora V. Hooper, Dan R. Littman, Andrew J. Macpherson. Science.](https://science.sciencemag.org/content/336/6086/1268)
*  [The immune system, adaptation, and machine learning, J. Doyne Farmer, Norman H Packard, Alan S Perelson.](https://www.sciencedirect.com/science/article/pii/016727898690240X)

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