Immune System: What It Is, Parts, Functions And Characteristics
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 favorable. 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 leaves it in the form of waste. The same thing happens in breathing. Unfortunately, this open exchange model not only allows living beings to ingest food and oxygen, but is also a free route for pathogens to enter the body.
Viruses, bacteria, viroids, prions, exoparasites, nematodes, flatworms and a long list of biological agents can take advantage of the entry routes of higher vertebrates (and invertebrates) and proliferate inside their host, although this is deleterious to it. in the short or long term. If you are interested in this premise, keep reading: today We tell you everything about the immune system, a biologically admirable defense mechanism with important connotations at both an evolutionary and physiological level. Do not miss it.
The National Cancer Institute (NIH) defines the immune system as “a complex network of cells, tissues and organs (and the substances they produce) that help the body fight infections and other diseases ”. This biological conglomerate is made up of white blood cells (leukocytes), special cell bodies, tissue structures and all 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 exogenous things (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 detect and limit the development of cancers as long as 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, since in reality, the limits between the two are not easy to establish. Before describing each of these aspects, two key concepts must be taken into account:
innate immune system
The innate immune system (IBS) is the host’s first line of defense Its members are, for the most part, recipients of pattern recognition that act in a general way in the face of a specific threat. They do not direct their range of action towards a single bacterial species or genus, but instead recognize particles classified in large groups and modulate their response in a generic way.
Furthermore, it is necessary to point out that not only cells are immune components In this category, for example, we find the skin (the largest human organ), sweat, saliva, behavioral acts (such as coughing or sneezing), tears and many other things. Without going any further, saliva, tears and mucus have bactericidal compounds that attack pathogenic organisms in a very general way. These first entry gates of the innate immune system are known as “primary biological barriers.”
On the cellular side, we can highlight macrophages These are cellular bodies that phagocytize all foreign bodies that enter the organism and present their antigens on their membrane surface, an act with which they activate the acquired immune system and its subsequent specificity. Macrophages are the perfect example of the first premise already mentioned (the innate immune system activates the acquired one in response to the entry of infections into the body).
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 summary, these entities act quickly and generally against endogenous and exogenous stressors.
The acquired immune system is one that learns after exposure to a pathogen, in order to be able to act against it more effectively in future contacts The fundamental properties of the acquired or adaptive immune system are the following:
We are not going to focus on the specifics of B and T lymphocytes, since its mechanism of action is very complex and we still have certain approximations to make. It is enough for us to know that, for example, T lymphocytes act in different ways when they are presented with an antigen from a microorganism, either destroying it (T cytotoxic), helping other immune entities (T helpers) or ending the immune response when the battle is over (T suppressors).
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 exposed to a pathogen for the first time, the B lymphocyte lineage creates memory cell bodies, which remember the characteristics of the pathogen. very accurately. So, With future exposures, antibodies are produced much more quickly and harmful microorganisms can be destroyed before they become a problem
The evolutionary significance of the immune system
Due to the anthropocentric view of human beings, there is a preconceived idea that all these responses and mechanisms are unique to our species. Nothing is further from reality.
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 capable of, for example, synthesizing bactericidal substances in the environment and thus killing their possible 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 made up of millions of different cell bodies and it is a machinery in constant synthesis that requires energy at all times to function correctly. . Responding to the exogenous is not free, and therefore, those who cannot afford it end up dying in nature.
With this premise, it can be theorized that the immune system has emerged 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 exposures. 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 condition.
So that, Every immune action generates a reaction of equal intensity in pathogenic populations The host-parasite relationship is based on an “arms race” type relationship: when the first generates a barrier, the second is selected over time to jump over it. This mechanism explains, for example, the emergence of bacteria resistant to antibiotics.
Summary
The immune system must be exact, fast, precise, have the ability to remember and be able to discern between what is internal and what is external. Unfortunately, sometimes this perfect biological gear fails, and takes with it all the benefits and answers that we have mentioned. In many autoimmune pathologies, lymphocytes do not detect the body’s autoantigens as beneficial, and end up attacking healthy tissues without any biological sense. This, without medication, would result in death in all cases.
In summary, the immune system is a necessary tool, but it can also fail over time. As the biological barriers of organisms evolve, pathogenic responses evolve with them, with the intention of being able to create an infectious condition one more day.
