The natural immunity acts spontaneously to avoid new or recurrent infections without apparent external support (Goldsby, Kindt, Osborne, & Kuby, 2014).
The immune system is a set of organs, tissues and substances whose main task is to protect the individual from the invasion of pathogenic organisms and cancer. To meet its objectives, it can generate a large number of cells and molecules that help identify the enemy and eliminate him through a complex series of processes..
Immunity - protective status against infectious diseases - includes innate and adaptive components. The former exist naturally based on the principle that the immune system possesses or creates defenses against antigens that it does not identify as its own and that are unknown to it..
Various authors have classified natural immunity in different ways, depending on its origin, activation, type of response or specificity (Innate Immune System, Wikipedia, n.d.).
Below are the most accepted classifications:
This type of immunity depends on the transfer of preformed defensive elements to a receptor. The best example is the passage of antibodies from the mother to the fetus through the placenta.
These antibodies, which are also found in breast milk, offer passive immunity to the infant. Protection against diphtheria, tetanus, rubella, measles, mumps, and polio has been proven in this way.
One of the most important characteristics of this type of immunity is its rapid onset and short duration, offering temporary protection immediately after birth or while breastfeeding lasts..
Passive natural immunity leaves no memory. This means that the person does not create defenses that remain in the body for a long time and could become ill from coming into contact with an infectious microorganism, regardless of whether in the past they have been protected thanks to foreign antibodies (Sun et al, 2011).
There are important differences between the immunity discussed above and passive artificial immunity. The latter is acquired by the individual when antibodies previously produced in laboratories with controlled environments are administered, unlike antibodies that are acquired from the mother, whose origin is natural..
In addition, passive artificial immunity is often used as a treatment to relieve symptoms of an existing medical disorder, in cases of congenital or acquired immunodeficiency, and to treat poisonings from snakebites or insect stings. On the other hand, passive natural immunity only offers protection against infections..
It is achieved with natural infection by a virus or bacteria. When suffering from the infectious disease, a primary immune response is developed, known as “first contact”, which produces immune memory through the generation of B and T memory lymphocytes..
If immunity is successful, subsequent exposures to the germ or "second contacts" will trigger an intensified immune reaction mediated by these memory lymphocytes that will eliminate it and prevent the disease that it causes from recurring (Scott Perdue and Humphrey; nd.).
The main difference with the active artificial immunity produced by vaccination is that in this one the disease is not suffered.
Although there is a first contact with the microorganism and the primary immune response is generated, as these are dead or attenuated germs that make up the vaccine, this reaction is very mild and does not cause the usual symptoms of the disease.
Innate natural immunity also encompasses physiological, anatomical, phagocytic, and inflammatory defense barriers. These barriers, without being specific, are very effective in preventing the entry into the body and activation of most microorganisms (Goldsby, Kindt, Osborne, & Kuby, 2014).
The skin and mucosa are the best examples of natural anatomical barriers. The skin has cells on its surface that neutralize germs through the production of sweat and sebum that inhibit the growth of most microorganisms..
The mucous membranes line the internal surfaces of the body and help in the production of saliva, tears and other secretions that wash and wash away possible invaders and also contain antibacterial and antiviral substances.
Mucus also traps foreign microorganisms in the mucosa, especially the respiratory and gastric, and helps in their expulsion..
The immune cells that make up the physiological defense barriers modify the surrounding pH and temperature, thus eliminating many local pathogens.
They also produce other substances and proteins such as lysozyme, interferon and collectins, capable of inactivating certain germs.
It is believed that one of the main characteristics of cells that participate in innate natural immunity is the property of pattern recognition.
It is about the ability to identify a specific class of molecules, which, being exclusive to certain microbes and never being present in multicellular organisms, are immediately identified as enemies and attacked..
Another innate defense mechanism is phagocytosis, a process by which a defensive cell - macrophage, monocyte or neutrophil - “swallows” material identified as foreign, either a complete microorganism or part of it..
It is a fundamental non-specific defense tool and is carried out in practically any tissue of the human body.
If, in short, some pathogen manages to circumvent all the previous barriers and causes tissue damage, a complex sequence of phenomena is triggered that is known as an inflammatory reaction..
This reaction is mediated by various vasoactive and chemotaxic factors that produce local vosodilation with the consequent increase in blood flow, increased vascular permeability with edema or swelling and finally the influx of numerous cellular and humoral elements that will be responsible for eliminating the invader..
Natural immunity can present important dysfunctions, some very frequent such as allergies and asthma and others not so common but very severe known as Primary Immunodeficiencies.
These manifest at an early age and are characterized by the presence of severe recurrent infections, very difficult to treat and that can even affect the normal development of the individual (British Society for Immunology, 2017).
There is currently a massive social movement against artificial immunization, whose main arguments are the possible adverse reactions of vaccines and the ability of the body to generate its own defenses, that is, Natural Immunity (College of Psysicians of Philadelphia, 2018).