The immune system is a set of very powerful organs and cells that enables you to cope with constant aggression from our environment, although it only accounts for 1% of the cells in our body.
However, repeated exposure to attack, certain nutritional deficiencies or poor lifestyle can disrupt the equilibrium of the system and weaken immunity. It can be bolstered through an appropriate diet, notably by taking probiotics, with the microbiota playing a vital role in sustaining immunity.
The body's 3 lines of defence
Immunity means the ability of the body to maintain its integrity by recognising and eliminating the diverse foreign bodies (antigens = microbes, allergens, foreign tissue…) that enter it. The defence system is composed of 3 main barriers, both physical and cellular, called the lines of defence.
• 1st line of defence: the skin and mucosa
The skin and mucosa represent the first natural physical barrier against attack. Composed of very tight epithelial cells, they are highly impermeable. This shield is frequently strengthened by the presence of hairs or cilia and by our bodily secretions that form a protective film (sebum, mucus). Certain of our organs (intestine, vagina, urinary tract, respiratory system) also have a protective layer made up of 'good' bacteria, commonly called the flora or microbiota. These bacteria notably prevent the adhesion and development of pathogens.
• 2nd line of defence: non-specific immunity
Should the first barrier be penetrated, the 2nd line of defence calls on the immune cells. This reaction is called non-specific as it reacts in the same way regardless of the aggressor. Multiple phenomena occur:
Certain white blood cells, the mast cells, recognise the foreign body and release chemical mediators of inflammation. These cause the vasodilatation of the blood vessels and the mass arrival of white blood cells to the location of the infection, accompanied by a sensation of heat, flushing, pain and swelling of the skin: this is the inflammatory response.
The chemical mediators also attract phagocytes, cells that destroy foreign bodies by 'consuming' them: this is phagocytosis.
The NK (natural killer) cells may also intervene; they destroy our own cells infected by the virus via proteins, the perforins, that trigger cell death.
• 3rd line of defence: adaptive specific immunity
Sometimes the innate immunity is not sufficiently powerful to eliminate the aggressor. In such cases specific immunity intervenes, calling on the T and B lymphocytes. It is called specific and adaptive as the response developed depends on the nature of the aggressor: on its membrane, each B or T lymphocyte carries a receptor able to recognise just one type of aggressor.
B lymphocytes: Produce antibodies, which attach themselves to and neutralise aggressors.
T lymphocytes:Killer cells kill the infected cells on contact.
The intestine, the key organ for the immune defences
Apart from its functions in digestion, the intestine plays a major role in the immune defence, containing some 70% to 80% of our body's immune cells. Mucosa cells, immune cells and the intestinal flora (hereafter called the microbiota) are intimately associated with maintaining the integrity of the system.
The immune cells receive information from the intestinal lumen (dietary components and also microbiota) as well as signals emitted by the mucosa cells. This dialogue triggers an immune response to combat the invasion of pathogenic foreign bodies via the intestine.
The microbiota: barrier and protection
The intestinal microbiota and all of the micro-organisms, mainly the bacteria Lactobacillus and Bifidobacterium, that colonise our digestive tract. It is composed of 100 billion bacteria, living symbiotically with our body, and weighing up to 2kg!
They contribute in numerous ways to maintaining the equilibrium of intestinal immunity:
Barrier against the adhesion and development of pathogens
Reduction of inflammation of the intestinal mucosa in the event of infectious gastritis
Trigger the production of protective intestinal mucus by the mucosa cells
Provision of energy to the cells of the intestinal mucosa for growth and renewal.
When the intestine becomes a sieve...
The intestinal mucosa and microbiota are fragile. Stress, an unbalanced diet, continued consumption of drugs, antibiotics and toxic substances can disrupt the microbiota (known as dysbiosis) or cause intestinal hyperpermeability: the intestinal mucosa no longer provides a barrier, letting infectious agents through.
Immunity can therefore be disrupted, leading to higher susceptibility to infection.
Nourish the microbiota to strengthen immunity
Fortunately, the equilibrium of the microbiota and the integrity of the intestinal barrier can be restored through the consumption of prebiotics and probiotics.
Prebiotics are dietary fibre that serve as food for the bacteria of the microbiota They are broken down into short-chain fatty acids (SCFAs) which include butyrate, acting as a fuel for the colonocytes.
Roles: Growth and development of the microbiota. Energy and renewal of mucosa cells. Strengthen the intestinal barrier.
Where are they found? In fruit and vegetables (artichokes, asparagus, bananas, onions, figs, Jerusalem artichoke, white part of the leek, onion, garlic...).
Also known as lactic ferments, the probiotics are bacteria, mainly lactobacilli and bifidobacteria.
Roles: Rebalance the microbiota. Improve transit and intestinal absorption. Inhibit the adhesion and growth of pathogens. Strengthen the immune system.
Where are they found? In yoghurt, fermented milk (kefir, ribot etc.), sauerkraut...