Immune system: what it is, parts, functions and characteristics.

An overview of the components and functions of the immune system, and its evolutionary utility.

All living beings on Earth are open systems. The cell, the minimum unit for life, must be able to interact with the environment to receive energy in one form or another, transform matter into metabolic products, and divide if conditions are conducive. Without the relationship with the environment, all these tasks would be impossible.

Based on this premise, processes such as respiration, nutrition, excretion and many other things are explained. Organic matter enters our body, we use it and it leaves it in the form of waste. The same is true for respiration. Unfortunately, this model of open exchange not only allows living beings to ingest food and oxygen, but is also a free pathway for pathogens to enter the organism.

Viruses, bacteria, viroids, prions, exoparasites, nematodes, flatworms and a long list of biological agents can take advantage of the entry pathways of higher vertebrates (and invertebrates) and proliferate inside their host, even if this proves deleterious to the host in the short or long term. If you are interested in this premise, read on: today we tell you all about the we'll tell you all about the immune systema biologically remarkable defense mechanism with important evolutionary and physiological connotations. Don't miss it.

What is the immune system?

The National Cancer Institute (NIH) defines the immune system as "a complex network of cells, tissues, and organs (and the immune system). cells, tissues, and organs (and the substances they produce) that help the body fight infection and other diseases". This biological conglomerate is composed of white Blood cells (leukocytes), special cell bodies, tissue structures and all the formations of the lymphatic system, such as the thymus, spleen, lymph nodes and bone marrow, among others.

At this point, it should be noted that the immune system not only fights against the exogenous (viruses, bacteria, etc.), but can also be activated by an internal failure, such as cell proliferation at an excessive rate. For example, Natural Killer (NK) cells help to detect and limit the development of cancers, as long as the tumor cells do not proliferate at an excessive rate.provided that the tumor cells do not go unnoticed.

From a functional point of view, the immune system can be classified as "innate" or "acquired". This classification is merely informative, as in reality, the boundaries between the two are not easy to establish. Before describing each of these strands, two key concepts should be kept in mind:

• The innate immune system activates the acquired immune system in response to the entry of infections into the body.
• The acquired immune system, on the other hand, uses the mechanisms of the innate immune system to suppress biological threats.

Innate immune system

The innate immune system (IIS) is the host's first line of defense.. Its members are mostly pattern-recognition receptors that act in a general manner in the face of a specific threat. They do not direct their range of action towards a single bacterial species or genus, but recognize particles classified into large groups and modulate their response generically.

In addition, it should be noted that not only cells are immune components. In this category, for example, we find the skin (the most extensive organ of the human being), sweat, saliva, behavioral acts (such as coughing or sneezing), tears and much more. Without going any further, saliva, tears and mucus have bactericidal compounds that attack pathogenic organisms in a very general way. These first gateways of the innate immune system are known as "primary biological barriers".

On the cellular side, we can highlight the macrophages.. These are cellular bodies that phagocytize all foreign bodies that enter the organism and present their antigens on their membrane surface, thus activating the acquired immune system and its consequent specificity. Macrophages are the perfect example of the first premise already mentioned (the innate immune system activates the acquired immune system in response to the entry of infections into the organism).

Fever, inflammation, the complement system and other cells (dendritic cells, neutrophils, eosinophils, basophils, mast cells and NK cells) are also part of the innate immune system. In short, these entities act rapidly and generally against endogenous and exogenous stressors.

Acquired immune system

The acquired immune system is one that learns after exposure to a pathogen in order to be able to act more effectively against it in future contacts.. The fundamental properties of the acquired or adaptive immune system are as follows:

• Specificity and diversity: the IBS acts in a general, pattern-recognizing manner. On the other hand, the acquired system responds individually to each pathogen (and its antigen).
• Memory: a primary lymphocytic response may be ineffective, but the organism remembers the pathogen in order to respond more effectively to it. Secondary responses are much faster and more lethal, thus preventing many infectious conditions.
• Lack of activity against one's own: the immune system must attack external substances by recognizing their harmful molecules (antigens). However, the body's own cells must present a series of molecules (self-antigens) that warn the lymphocytes that they should not be attacked.

We are not going to focus on the specificities of B and T lymphocytes. B and T lymphocyteslymphocytes, since their mechanism of action is very complex and we still have some approximations to make. It is enough for us to know that, for example, T lymphocytes act in different ways when presented with an antigen of a microorganism, either by destroying it (cytotoxic T), by helping other immune entities (helper T) or by terminating the immune response when the battle is over (suppressor T).

On the other hand, it should be noted that the key to the memory of the acquired immune system lies in the proliferation of B lymphocytes. When first exposed to a pathogen, the B lymphocytic lineage creates memory cell bodies, which remember the characteristics of the pathogen very accurately. Thus, antibodies are produced much more quickly upon future exposure, and harmful microorganisms can be destroyed before they pose a problem..

The evolutionary significance of the immune system

Due to the anthropocentric view of the human being, there is a preconceived idea that all these responses and mechanisms are unique to our species. Nothing could be further from the truth.

All living forms on Earth respond in one way or another to external pathogens, without exception.. Although some living beings do not have an immune system as such, they are able, for example, to synthesize bactericidal substances in the environment and thus kill potential competitors.

Although it is a more ethereal concept than the heart or the brain, it is necessary to put the immune system in perspective: it is composed of millions of different cell bodies and is a constantly synthesizing machinery that requires energy at all times to function properly. Responding to the exogenous is not free, which is why those who cannot afford it end up dying in the wild.

On this premise, it is possible to theorize that the immune system has arisen solely in response to external stressors.. If a pathogen appears in an ecosystem, the immune system tries to recognize it, eliminate it, and remember it for future exposure. On the other side of the coin, the microorganism will mutate rapidly in each generation, with the "intention" of not being recognized by B lymphocytes in the next infectious picture.

Thus, every immune action generates an immune reaction, every immune action generates a reaction of equal intensity in the pathogenic populations.. The host-parasite relationship is based on an "arms race" type relationship: when the former generates a barrier, the latter is selected over time to bypass it. This mechanism explains, for example, the emergence of antibiotic-resistant bacteria.

Summary

The immune system must be accurate, fast, precise, have the ability to remember and be able to discern between the internal and the external. Unfortunately, sometimes this perfect biological gear fails, and takes with it all the benefits and responses we have mentioned. In many autoimmune pathologies the lymphocytes do not detect the autoantigens of the organism as beneficial, and end up attacking healthy tissues without any biological sense. This, without medication, would result in death in all cases.

In short, the immune system is a necessary tool, but one that can also fail over time. As the biological barriers of organisms evolve, the pathogenic responses evolve with them, with the intention of being able to create an infectious picture one more day.