Diseases, lifestyle, genetics, food.... are concepts associated with the immune system, but what do you know about your body's main defence? We talk to you about this important set of organs and cells that form an effective barrier.

Before birth, our body tolerates cells foreign to its own organism. When our skin, bones and even our ability to hear are being formed, proteins and substances are constantly reaching the foetus through the placenta. At this delicate time, the tiny body is already defending itself. And it does so in a more peaceful way than an adult body, because it regulatory T lymphocytes do not mark the foreign material to attack it but have a adaptive response.

As we are born and grow older, our bodies evolve, but the immune system that defends us is largely the result of those nine weeks of gestation and adaptation.

Such a simple idea has behind it a a complex system of organs, tissues and specialised cells, the white blood cells or leukocytes.

Liver in the foetus and bone marrow in adults, are the primary organs of the immune system. Both are responsible for the maturation of B-lymphocytes. T-lymphocytes mature in the thymus, an endocrine gland. The B- and T-lymphocytes are a type of white blood cells that are responsible for identifying antigens through antibodies and for recognising and attacking foreign objects, respectively.

In addition to B and T lymphocytes, there are the "natural killer" lymphocytes, lymphocytes capable of destroy virus-infected cells and tumour cells.

The lymph nodes, tonsils, Peyer's patches, spleen, and lymphoid tissues associated with mucous membranes, are secondary organs that provide the environment that lymphocytes need for their proper functioning.

The white blood cells are the body's main defence cells and have different specialisations:

• The granulocytes circulate in the blood and travel to tissues during the inflammatory response. In addition, together with monocytes, they generate precursors that leave the bone marrow. Within granulocytes, the neutrophils are the first cells to reach the infectious focus. and its effectiveness, can be just as destructive to the body's own cells.
• The monocytes are specialised macrophages that reside in the lung, liver, kidney, brain, bone, spleen or lymph nodes.
• The dendritic cells play a super-specialised role in activating and "instructing" lymphocytes.
• The lymphocytes recognise and attack foreign cells.

The role of the gut ecosystem

The gut is the organ where the largest part of the immune system resides.

On the one hand, the gut microbiota sbinds to the intestinal mucosa acting as a barrier that prevents pathogens from colonising the gut. The microbiota is made up of trillions of bacteria that live together in a balance that poor diet and antibiotic use do not.

The lymphoid tissue housed in the intestine, forms the most important protective barrier: Peyer's patches and mesenteric lymphoid nodules are part of this system in which many types of cells associated with the immune system also coexist.

In addition, the intestinal epithelium also constitutes a protective barrier with a large number of specific cells.

>> KNOW THE STATE OF YOUR GUT HEALTH

What are the threats to our defence system?

 The bacteria and viruses, toxins, cancer cells, and other people's blood and tissuesare threats to the body throughout our lives. They may not cause disease on their own, but are combined with other factors that make some people more or less affected: our lifestyle or the environment in which we move, even the internal environment affects our health.

However, the decisive factor that influences our immune response is the genetic factorwhich determines whether our immune system is strong under normal conditions.

The human body's defence system has also evolved. While the risk of infection decreases, inflammatory and autoimmune pathologies are becoming more and more frequent. At a time when a virus has brought about a worldwide pandemic and hundreds of thousands of deaths, it seems irrelevant to talk about this evolution in the type of pathologies we suffer from, but the truth is that, in general, We are seeing more and more of these diseases. 

Why don't we get the same disease twice?

Our immune system is made up of several immune systems. The innate, acquired and passive. Innate immunity is the immunity we carry "as standard" when we are born and is made up of a system of barriers that protect us.

These barriers are, among others, skin, cough reflex, mucus... More precisely, these barriers can be cytokines, physical-chemical (skin, mucous membranes, cilia of the nose and trachea...), cells (mononuclear phagocytes and neutrophils) and soluble factors (lysozyme, mucus, germs of the vagina, skin and intestine, among others).

The acquired immune system is formed by what we call "immune memory". and complements the innate immune system. When we contract a disease, it is because a pathogen has come into contact with our body. From that moment on, cells called B lymphocytesThe microbes generate antibodies that remain in our body. When the same microbe enters our body, our body is already able to recognise it and triggers the immune response to defend itself.

We can say that in the first "attack", the pathogen takes our organism by surprise and attacks it. At the same time, our immune system defends itself, which is why we have a fever, for example. Thanks to the development of antibodies, if a second attack occurs, the foreign agent is already recognised and the body can act in time. For this reason, there are diseases that we only get once in a lifetime.

Passive immunity is the borrowed" protection such as that provided by breast milk or vaccines, for example.

Factors that weaken the immune system

Intestinal Candidiasis. Infection with candida albicans destabilises the balance of the intestinal microbiota. Candida is an invasive fungus that also spreads from the gut to the mucous membranes of the mouth, skin or sexual organs.

This disease can affect intestinal permeability, allowing bacteria to enter the bloodstream.

Antibiotics. Antibiotic use can have a serious side effect - it can wipe out the good bacteria in our gut. Further, it has been found that the antibiotic can affect the microenvironment of the infection, causing changes that protect the bacterial pathogen.

Ageing. Ageing also affects the functioning of the immune system: it responds more slowly to attack the pathogen, and also in healing. It also decreases the ability to detect and correct cellular defects such as those that cause tumours.

Although ageing cannot be prevented, we can take action to reduce the effects on our immune system: physical exercise, diet, and control of alcohol and tobacco consumption are factors that can keep our immune system stronger.

Psychological factors such as stress or anxiety can weaken our immune system and increase the likelihood of inflammatory or autoimmune diseases.