The immune system uses three interdependent lines of defense. Their integrity and efficiency must be consistently supported with essential micronutrients.
Supporting the full efficiency of the immune system is essential to protect health and well-being at any age and under any circumstances. To do this it is essential to follow a healthy and balanced diet, regularly practice moderate physical activity, avoid situations of stress and psychophysical fatigue, rest enough and, last but not least, maintain a positive attitude towards life, because it has been shown that even the mood affects to a non-negligible extent on the body’s immune defenses.
In this context, nutrition, which should be rich in fruit and vegetables in particular, plays a key role because, to function at their best, the multiple components of the immune system need energy and a whole series of essential micronutrients capable of supporting its integrity, vitality and reactivity.
Knowing what are the fundamental immune components and mechanisms and which vitamins and minerals are necessary to support them allows us to identify situations at risk of deficiency and correct them through appropriate dietary choices.
The human immune system
All living organisms (i.e. animals, plants, bacteria and fungi) are endowed with an immune system characterized by one or more lines of defense and a variable complexity depending on the evolutionary level and the type of protection they need.
The human body is characterized by an extremely articulated defense system against external aggressions that includes physical and chemical barriers, different types of cells involved in the recognition, aggression and destruction of pathogens, countless substances with inflammatory, cytotoxic and immunomodulatory activity and antibodies. Each of these elements acts in a strictly planned and coordinated manner with the others, according to precise methods and timing, in order to offer maximum protection to the body.
Innate immunity: physical and chemical barriers
The physical barriers that protect us from the outside world are represented by the skin and mucous membranes of the respiratory tract, gastrointestinal tract, urinary tract and genital tract. To these, there is an additional internal barrier called the “blood-brain barrier” which serves to offer additional protection to the central nervous system, to minimize the likelihood that viruses and bacteria accidentally entered the body can reach and damage the brain and spinal cord.
These barriers offer a non-specific and immediate defense against pathogens and constitute the main structures of the so-called “innate immunity”. Various chemicals with antimicrobial action also contribute to ensuring this type of immunity, such as defensins (present in the skin, respiratory mucous membranes and seminal fluid), lysozyme and phospholipase A2 (two enzymes present in saliva, tears and breast milk), as well as pH that tends to be acidic. (from pH 5.5 of the skin to pH 1.0-2.0 of gastric secretions) which discourages the multiplication and engraftment of fungi and pathogenic bacteria.
Even the endogenous microflora of skin and mucous membranes (especially genitourinary and gastrointestinal ones), consisting of non-harmful commensal microorganisms, exerts a protective role against fungi and bacteria, both through the modulation of local pH and through competition for nutrients, essential microelements (such as iron) and space available for growth.
To combat bacteria directly and immediately, innate immunity also makes use of substances with inflammatory activity, such as prostaglandins, which trigger the inflammatory process and increase the blood supply in the area affected by the infection (on which typical signs and symptoms such as burning, redness, swelling and pain depend), and leukotrienes, which recall on site some subgroups of white blood cells (leukocytes ) who will have the task of attacking the invaders.
Innate immunity: cellular barriers
All the components mentioned above represent the first level of innate immunity. The second level is represented by different types of white blood cells, which include phagocytes (including macrophages, neutrophils and dendritic cells), lymphocytes, mast cells and eosinophilic and basophil granulocytes.
All these cells, present mainly at the tissue level, have the task of attacking, incorporating and destroying infectious agents that accidentally entered the body (directly implementing phagocytosis or promoting it) and helping to regulate the different phases of the inflammatory response. Macrophages and dendritic cells also act as a link between innate and “adaptive” immune response, i.e. based on the production of antibodies and the resulting “immunological memory”.
A particular type of lymphocytes belonging to the system of innate immunity, the natural killers or NK, are not involved in the fight against aggressions by external agents, but protect the body from potentially harmful cells produced by mistake by the body itself during tissue renewal, eliminating them. This selective destruction action, although not 100% efficient, greatly reduces the risk that genetically altered cells can give rise to tumors.
Adaptive immunity
When the set of mechanisms of innate immunity is not sufficient to eliminate pathogens present in the blood or tissues, adaptive immunity intervenes. This response is based on a slower, but more powerful and extremely specific reaction,which also involves the production of antibodies and increases the body’s ability to react to infectious agents of the same type that it will encounter later.
The adaptive response is antigen-specific: it requires the recognition of antigens (specific “non-self” molecules, i.e. foreign to the body) during a process in which cytotoxic T lymphocytes and helper T lymphocytes (cell-mediated response) are mainly involved together with B lymphocytes (humoral response).
Cytotoxic T lymphocytes trigger the production of substances and a whole series of reactions that determine the destruction of the infected cell. Helper T lymphocytes, on the other hand, produce substances that have the task of promoting cell-mediated and humoral response.
The humoral response is mediated by B lymphocytes which, once in contact with specific antigens present on the membrane of a pathogen, are transformed into cells that produce antibodies. Released into the blood and lymphatic system, the specific antibodies thus produced recognize with extreme precision the pathogen or infected cells characterized by that antigen and bind them to “brand” them as dangerous and trigger the series of reactions aimed at their destruction (complement activation and phagocytosis).
Once the pathogen is completely eliminated and the disease defeated, antibodies stop being produced, but the body maintains their “memory” by retaining a small group of cells capable of promptly producing antibodies of the same type, should a new pathogen with the same antigen enter the body in the following months or years.
The human genes responsible for the production of antibodies are about 30,000, but the immune system is able to produce antibodies that are able to recognize virtually all the possible substances with which the body can come into contact (theoretically infinite), thanks to an extremely flexible modular construction process and imperceptible causal genetic mutations.
Functions of the immune system
The immune system works every second, incessantly, to protect the human body from viruses, bacteria, fungi and potentially harmful foreign substances with which we come into contact, more or less consciously, at all times, as well as from an unknown number of aberrant cells produced by mistake by the body and which, if not immediately eliminated, could give rise to serious diseases, Like tumors.
Yet, its activity is noticed only when the response it triggers is striking, as happens in the case of influenza, bacterial infections, exanthematous diseases or allergies, or when for some reason the body’s immune defenses begin to work too much, triggering autoimmune diseases, or too little, giving rise to immunodeficiency situations that increase the propensity to be affected by infections of various type.
The organs of the immune system and their functions
In some ways, even the aforementioned physical barriers consisting of skin and mucous membranes can be considered organs of the immune system; however, strictly speaking, this term refers to bone marrow and thymus (primary lymphoid organs) and lymph nodes, lymphatic vessels, spleen, tonsils and Peyer’s plaques present in the wall of the intestine (secondary lymphoid organs), i.e. the organs and tissues that predominantly produce, host or transport immune cells.
The bone marrow, present inside the spongy bones, is one of the main tissues in which the progenitor immune cells are continuously produced from which B and T lymphocytes, monocytes and the various types of granulocytes will derive for successive differentiation and maturation steps.
The thymus, a small organ located in the center of the chest, is instead crucial for the “maturation” of T lymphocytes (especially after birth, less in adulthood): it is at this level that the T lymphocytes produced by the bone marrow and still “virgin” learn to recognize foreign antigens and to distinguish the “non-self” from the “self” (ie to distinguish the molecules that must trigger the inflammatory / immune reaction from the harmless ones).
Lymph nodes and lymphatic vessels constitute, respectively, the peripheral stations and the “junction roads” of the lymphatic system, distributed in all districts of the body. In lymph nodes, immune system cells such as lymphocytes and macrophages concentrate to perform part of their functions, moving through lymphatic vessels when needed.
In some districts of the body, the lymph nodes are aggregated in a peculiar way and are indicated with specific names: this is the case of Peyer’s plaques of the intestine and the tonsils present in the pharynx (where they represent important, although not essential, defense posts against infectious agents that affect the respiratory tract and responsible for typical seasonal ailments).
The spleen, located on the left in the upper abdomen, is also an often underestimated lymphatic organ, but precious since it contains lymphocytes and plasma cells and helps to eliminate bacterial infections more effectively, reducing the risk of severe complications. Suffice it to say that splenectomized people (ie who have had their spleen removed for various reasons) must undergo specific vaccinations (in particular, against meningococcus and pneumococcus) and antibiotic prophylaxis in case of influenza, tooth extractions or other procedures at risk of infection to avoid septicemia (serious blood infections).
Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.
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