How does the body defend itself from disease and infection?

In the last months, we have all wondered if our body is prepared to defend itself against the COVID-19 virus. Antonio Martín Duce, Professor of Physiopathology at the University of Alcalá, explains how the human body defends itself from what can kill us for the digital diario uah.esnoticia.

- Now that we are living in a time when public opinion is very concerned about its health and the functioning of its organism, how does our body deal with disease and aggression?

The human body is made up of a huge number of cells in which millions of molecules, in perfect order and harmony, maintain life. All this, forming a complex communication network that, under the direction of the nervous system, allows you to warn, prepare, face and, usually defeat all those agents, external (bacteria, pollutants…) or internal (mutations, diseases...) that compromise your life.

The human body is an extraordinary complex machine, we can say that it mixes mechanical crafts and digital development, all based on DNA, a real manual where the formation of the main molecules that will help us survive is collected: proteins.

Our body uses several protective mechanisms, such as immune surveillance, based on specific defense cells such as leukocytes, mainly lymphocytes and phagocytic cells, as well as similarly specialized defensive molecules; all of them being part of the great protector of human life such as inflammation is.

The organism also has natural barriers, as walls, such the skin, various secretions, etc. In other cases, connective tissue is in charge of helping in this fight from healing. To keep all these resources active, it´s essential to have a proper functioning of vital organs (brain, heart, lung, kidney, liver, endocrine, etc.), in addition to having a sufficient supply of water, oxygen and energy.

- How do mutations work? How does DNA protection equipment work?

We say that a mutation occurs when something changes in the normal structure of DNA, from a simple nitrogen base to complete fragments of a chromosome. It can be produced in non-sexual body cells, which will not transmit to offspring, or in sexual ones and so we will have inherited diseases. Any mutation will involve the formation of an abnormal protein and thus the risk, never safety, of disease.

It´s estimated that every second 25 million cell divisions occur, only 10% of them to maintain our red blood cell numbers. But, for every 100.000 nitrogen bases that are incorporated into DNA, one is wrong. This situation would involve millions of mutations that would make life impossible. Fortunately, the body has supervisors, such as the p53 protein or 'genome guardian', which stops the duplication process if it detects an error, and other healing proteins, which remove the defective molecule. Only this can reduce errors by 100 times. 

Antonio Martín Duce interior
Antonio Martín Duce

The DNA molecule has two equal chains. This duplication is a safety because, in the face of the mutation in one chain, the other will serve to maintain the correct sequence by introducing the correct base. In other cases, the organism directly removes a chain fragment and a protein, DNA polymerase, is responsible for filling the gap correctly, following the pattern. Even when the two chains are mutated, the body can cut the wrong fragments and splice them together, some links will be lost, but the chain will remain active and correct.

Finally, when it is noticed that repair will not be possible, there is still something to be done to defend itself, apoptosis. That is, to cause the death of the damaged cell so that it does not perpetuate and harms the rest. On the other hand, as prevention is more than cure, the organism maintains a strict follow-up of molecules that facilitate mutations. An example is the antioxidants that it puts into operation to fight the known and harmful oxygen radicals.

- The body lives with thousands of infections every day, how does it do it?

Really, the body does not live with infection but with microorganisms, mainly bacteria, but also viruses, fungi and others. Evolution has allowed us to find, in part, a friendly agreement with multiple bacteria and, in exchange for heat, moisture and food, that is ideal conditions that they find mainly in our digestive system, skin or vagina, make life easier for us. This so-called microbiota synthesizes vitamins, digests fiber and, above all, fights on our side against the aggressor bacteria by competing with them for space or food or directly attacking them.

On the other hand, we all possess what is called innate immunity, which is nothing but natural barriers that we possess to combat the entry or development of germs into our body and therefore the appearance of infections. Some of them are physical barriers such as skin; chemicals such as stomach acid;cells, such as lymphocytes or molecular cells, such as antibodies.

- Does the human body have other mechanisms that can draw attention to us about a poor state of health?

Most commonly, the body warns us that something is malfunctioning through signs (objective manifestation of a disease) and symptoms (subjective manifestation).

Among the first, it´s worth highlighting, for its ease of diagnosis, all those that happen on the skin, such as dryness, color change or temperature....The symptoms include pain or tiredness, although many of them will depend on the organ involved, nausea or vomiting if it is the digestive system; cough or dyspnea if it is the respiratory system, etc. In serious illnesses, the so-called constitutional syndrome, consisting of tiredness, loss of appetite and weight, must alert us.

- What tips do you recommend to protect your immune system? Any specific to COVID-19?

Really to prevent us from COVID-19 there is no treatment. Although it seems logical to think that losing weight to figures close to the ideal weight, keeping blood glucose and blood pressure at normal, or avoiding tobacco are healthy measures given the factors that make this picture worse, obviating the impossibility of acting on age.

Publicado en: Inglés