By: Mohammad E. Shbair, IUG Virus and Immunity Instructor.

Children's Immune System is less infected With COVID19, Why?

04 - May - 2020

By: Mohammad E. Shbair, IUG Virus and Immunity Instructor.

While the novel coronavirus SARS-CoV-2 has emerged and therefore the COVID-19 illness also has spread, scientists has noticed that children who tested positive are way less than the elderly. A statistical study conducted in China showed that less than 19-year aged infected people make 2% out of a sample composed of 72314 patients. Also, in the United States, the percentage was less than 1% out of a sample of 508 patients. This phenomenon is prominent in all the countries that the pandemic has hit. A comprehensive look at the immune system, the first to defend the body, would interpret this phenomenon. And by defending the body we mean resisting the virus and avoiding its fatal effects. It is worth noting that children in our content means those who have their immune system mature enough, excluding infants who have no mature immune system.

Immune System Development

The components of the immune system begin to appear during the fetal stage. Scientists have observed that both T-cells, responsible for cellular immunity, and B-cells, responsible for forming antibodies, appear in the fetus’s spleen in around the 14th and 18th weeks since the beginning of pregnancy. After birth, with the newborn reaching the fifth month, all these molecules appear on the cells of the child just like those of the adults. However, these cells do not reach the peak of their activity due to the secretion of small quantities of cytokines such as γIL-2, IL-4, IL-5, IL-12, INF- are the compounds that regulate the immune system's action in resisting foreign bodies. They also play an important role in the inflammatory response as we illustrate in a moment.

Between the sixth and ninth months, the immune system of the newborn begins to respond strongly to the compounds on the surfaces of the microbes such as the glycoproteins that viruses use to identify the receptors on the target cells in the host's body. After the first year, the immune cells respond to polysaccharides on the covers of many pathogenic bacteria.

During pregnancy, immune memory cells are activated in the body of a pregnant woman and a large number of antibodies are being constructed. These antibodies, directed against many types of microbes, are IgG. They are pumped through the placenta into the blood of the fetus to give it immunity to those microbes during the first months of birth.

 It takes the body of the newborn a period ranging from seven months to twelve months since birth, so that the level of IgG and IgM antibodies in the body is 50% of the level in adults. Whereas, IgA antibodies reach that level within three to five years. There is no doubt that vaccination programs known to all give children immunity against many infectious diseases for a long time. Through this process, the herd immunity or community immunity is realized for these diseases.

It is worth noting that breastfeeding is necessary especially in the first days of birth since mother's milk has multiple immune components enhancing the infant's immunity against many infectious diseases. The immune system, with its various components, resists the viruses that invade the respiratory system. Th-1 cells activate the macrophages called Macrophage with its stimulating cytokine secretion (IFN-γ). This secretion in turn destroys the viruses and then prepares the stage of antibody production by B cells. The cells responsible for Cellular immunity (CD8, NK) are activated which plays an important role in killing virus-infected cells.

Inflammatory Response

This phenomenon is considered a natural response to the immune system dealing with foreign bodies that may reach the body, such as bacteria and viruses, and it is carried out in several stages. What concerns us at this stage is dealing with viruses that affect the respiratory system. In the early stages, monocytes and macrophages cells are activated and produce many cytokines, such as TNF-α.

This secretion causes the expansion of capillaries at the point of infection and then stimulates multiple types of white cells, the most important of which are Neutrophils; to reach this point. Another group of cytokines (IL-1β, IL-6, Il-8, INF-γ) contributes to this process. Likewise, TNF-α binds to receptors on the affected cells and causes the death of those cells. The lungs have a special macrophage called Alveolar Macrophage that secretes the same types of previous cytokines and boosts the immune response.

In the second stage, the dendritic cells and macrophages cells deal with the virus and show the important compounds in the pathogenic process to be identified by T cells, which in turn activate B cells through specific cytokines and then create antibodies. Simultaneously, the cells of the cellular immunity are activated, the most important of which are cytotoxic-T cells to deal with the infected cells and eliminate them.

Some phenomena accompany the inflammatory response, such as fluid accumulation, pain and high temperature. All these phenomena come in response to some substances produced by immune cells, such as Serotonin, Bradykinin, Prostaglandins. The goal of the inflammatory response is primarily to protect the body from harmful microbes,

However, in case the immune system fails as a result of the imbalance between the virulence of the virus and the immune components, severe inflammation of the lung, pneumonia, may arise. The alveoli are filled with pus and fluid. And this impairs the lung's ability to supply other organs such as the kidneys with oxygen. This lack of oxygen decreases kidneys' function and may lead to kidney failure. This indeed is that which has taken lives of many of those who were infected with the emerging coronavirus. And possibly other vital organs of the body may have failed. The main reason for all this imbalance is the overflowing of cytokines and causing what is known as Cytokine storm, which causes severe fever in addition to the aforementioned pathological phenomena.

Low percentage of children infected with this disease

It's obvious that children might be infected with the SARS-cov-2 virus, but the question is why do not they show symptoms that adults suffer from? And why do they suffer from complications resulting from the virus? Why does another virus, such as the flu, often cause severe symptoms?

Immune response for children is obviously different from that of adults. It is notable that cytokines storm which is a strong immune response that may result in lungs' destruction doesn’t not appear for children as their immune system still is not mature enough to strongly respond. The antibodies that children form as a result of receiving different vaccinations and exposure to other pathogens, may interact with components in the emerging corona virus and thus neutralize it. It is also obvious that the thymus gland in children, which is responsible for the production of T cells, the main component of cellular immunity; is more active because of their atrophy with aging. SARS-COV-2 receptors, which are ACE-2, are not found in a large number in the lungs of children as for adults, thus avoiding severe lungs infection.

Adults are more susceptible to complications from the virus, as many of them suffer from other diseases that represent a burden on the immune system such as diabetes, high blood pressure, heart diseases, and others. The active movement and good nutrition of children may strengthen their immunity, which will contribute to overcoming the virus. Finally, it has been shown that the antibodies formed by the immune system of adults are not as strong as those formed in children. Active research is still is still wholeheartedly conducted to find out what it is and the nature of this virus and develop treatments and vaccines, and there are many questions that need to be answered, including:
Do the antibodies formed by the immune system work effectively against the virus, or are there mechanisms used to overcome these bodies as HIV virus and the bacteria that cause syphilis do? Does it have the ability to manufacture his own proteins similar to those of the immune system to deceive this system? Do the genetic changes of the virus contribute to the severity of infection and repeated infections of the same person? If scientists would be able to neutralize ACE-2 receptors, would they ensure that the virus did not search for other receptors to enter cells? Does the virus go through a period of latency in the body in organs far from the effects of the immune system, such as the Herpes virus? Are the symptoms that have appeared in the nervous system, such as loss of sense of smell and other symptoms caused by the virus itself? Or is it an inflammatory response to the immune system and one of the consequences of the so-called cytokines storm? These and other questions will be answered by scientists in the near future and in light of the steady progress in the methods of biotechnology and in cooperation between research teams in different countries, if any. We are still emulating what scientists were doing in the nineteenth century of developing theories and then trying to prove them by practical methods and accurate observations. The battle between us and the virus may last for some time yet our hope will save us as we pray that god may cleanse this epidemic and save all humanity.