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The human immune system fights disease. As a result, some people may not become infected or have the disease in a mild manner. Resistance to COVID-19 may depend not only on vaccines and exposure to the virus, but also on lifestyle or chronic diseases.
- Scientists are constantly trying to explain what causes some people to become infected with COVID-19 and end up in the hospital in a serious condition, while others have the disease asymptomatically or not at all
- Certain genetic characteristics may be responsible for this, but also chronic diseases. And not always in a negative way. Some of them may even reduce the risk of disease
- Certain factors also affect the course of the disease caused by SARS-CoV-2. Some of them affect the risk of severe course of the disease
- You can find more such stories on the TvoiLokony home page
Immunity to infectious diseases. How it’s working?
We fight viruses primarily with NK lymphocytes, known as natural killer, which are an element of cellular immunity. However, in practice, antibodies are also needed to successfully combat viral infections. In the first phase of infection, the mechanism of innate (non-specific) immunity works mainly, and the formation of specific antibodies is noticed only in the 2-3nd week, when a large number of cells attacked by the virus begin to break down.
The main task of the immune system is to distinguish self from foreign cells. The function of the “identity card” is performed by the histocompatibility system, and in it – MHC I and MHC II molecules, recognized by the immune system. Intruders “without good papers” (bacteria or cancer cells, for example) are destroyed… or at least they should be.
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MHC I and MHC II not only “label” cells, but are also involved in presenting foreign proteins to the immune system. If the MHC I molecule does this, the body produces a cell-mediated immune response, and if the MHC II molecule it produces antibodies produced by B lymphocytes (humoral response). Antibodies by binding to a specific target “mark” it for attack through various mechanisms – for example, macrophages, K cells, and the complement system. The antibodies themselves can also block viruses or neutralize toxins like snake venom.
Immunity works more efficiently when the intruder has already made himself known – it’s as if a wanted poster has been sent. The viruses can be a previous infection or a vaccine. The vaccine does not have to contain the whole virus, a “special sign” is enough – in the case of SARS-CoV-2 it is protein S.
If the foreign protein is absorbed by the cell from the outside (as in the case of a vaccine containing the finished coronavirus spike protein), the MHC II molecule presents it. On the other hand, a foreign protein that was created in the own cell (e.g. a coronavirus spike protein produced on the basis of an mRNA recipe from a vaccine) is presented to the immune system by the MHC I molecule.
What determines the resistance to COVID-19?
However, there are people who – for various reasons – “cannot” be infected with a virus that they have not encountered before. The HIV virus that attacks the immune system and causes AIDS is a special case. The mutation of the gene responsible for the production of the CCR5 protein present on the surface of the immune system cells means that the HIV virus is unable to infect these cells, which ensures resistance to infection. This mutation occurs in 5–14 percent. Europeans, however, is rare among Africans and Asians.
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Until recently, coronaviruses seemed relatively harmless – they accounted for 10-20 percent. colds. Their more dangerous varieties, however, had their own permanent animal reservoir from which they could jump over to humans. First, the SARS virus (2002) succeeded – 794 deaths, then MERS (2012) – 858 deaths. However, the truly global problem emerged in 2019, with the SARS-CoV-2 virus that causes COVID-19.
To get into our cells, the SARS-CoV-2 virus uses ACE-2 receptors. The mucosal cells have the greatest number of these receptors – in the upper respiratory tract, but also in the intestines and the brain.
Experts in the field of immunology, genetics and bioinformatics estimate that people with certain genetic characteristics may have a potentially greater susceptibility to coronavirus infections. A number of variants of the human ACE2 gene have been identified that may affect susceptibility to infection with human coronaviruses. People with specific genetic characteristics, such as gene variants, have different susceptibility to infections and react differently to drugs used in therapy.
Severe or mild COVID-19?
The course of COVID-19 may also be influenced by the age of patients, but also by comorbidities such as diabetes or hypertension, the causes of which may also depend on genetic conditions and lifestyle. Paradoxically, in the case of asthmatics and allergy sufferers (taking steroid drugs) infection with coronavirus is less frequent, and in the case of falling ill, the course is less severe. Additionally, the pandemic-related use of face masks when outdoors reduces exposure to allergens such as tree pollen.
- Also check: After an mRNA vaccine, the risk of a severe course of COVID-19 increases? It’s a myth
In addition, the mild severity of SARS-CoV-2 infection may be related to the fact that the person has had a history of infection from other coronaviruses that cause the usual seasonal colds. The immune system works more efficiently when the intruder has already made himself known – it is just as if a wanted poster was sent. The viruses can be a previous infection or a vaccine. Infection with the rhinovirus, which causes the most common colds, also makes it difficult to get infected with the “competitive” coronavirus SARS-CoV-2, research published in The Journal of Infectious Diseases has shown.
In contrast, some people have an overreaction of the immune system to the infection. Instead of the gradual suppression of inflammation, there is an uncontrolled increase in inflammation, which creates the risk of the so-called a cytokine storm.
In turn, children rarely get COVID, which, according to specialists, is related to the fact that vaccines for other diseases taken at this stage of life stimulate the immune system. In addition, the “childhood” ACE-2 receptors, which allow the virus to enter cells, are less accessible than in adults.
The long-term resistance to COVID-19 that convalescents achieve is still unknown. Most likely, the stronger the infection was, the greater the immunity will be.
The results of a study by Italian scientists recently published in the “Viruses” journal showed that the neutralizing antibodies produced by the body after infection with SARS-CoV-2 are present at a significant level 11 months after the infection. Thus, they confirmed the hypothesis that immunity may be longer than 8-10 months, which is currently discussed in specialist publications.
Also, no vaccine gives 100 percent. protection. Some vaccinated people may still get sick or transmit the virus – in about 10% of those vaccinated. the vaccinated does not develop immunity (PAP)
Author: Paweł Wernicki
pmw / agt /
Also read:
- You don’t have to disinfect everything? Experts change recommendations
- Experts: we will win with the pandemic if 60 percent. the population will wear masks and keep their distance
- Grzesiowski: «drive thru» vaccination points break safety rules. Vaccination is not fast food
- Will there be consequences for people not getting the COVID-19 vaccine?
- How many people in Poland died or had thrombosis after vaccination? New data
- Will it also be possible to mix COVID-19 vaccines in Poland? The Ministry of Health responds
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