Immunologist: the probability of secondary infection is very low

The novel coronavirus (2019-nCoV) of Wuhan has been infected by tens of thousands of people for its treatment by its super human transmission With the passage of time, more and more patients are cured and discharged after treatment Because of the spread of the virus, these cured patients may be exposed to the virus again Will they have a second infection? In response to this question, Huang Bo, deputy director of the Institute of basic medicine of the Chinese Academy of Medical Sciences, distinguished professor of Peking Union Medical College of the Chinese Academy of Medical Sciences and vice president of the Chinese society of immunology, replied to the media that the answer is generally that there will be no secondary infection, which is mainly determined by the nature of the immune system of the organism and the location of the virus mutation Huang Bo made the following detailed explanation from a professional point of view: the human immune system consists of two parts: the innate immune system and the acquired immune system In the course of life evolution, the innate immune system first appeared in the very low living organisms, while the acquired immune system only existed in vertebrates Innate immune response is rapid, but lack of specificity Acquired immune is only activated when innate immune cannot be controlled, but it is highly precise and specific When the virus invades the body (for example, the coronavirus invades the respiratory tract mucosa), the macrophages in the innate immune system quickly engulf the invading virus, while the natural killer cells attack the infected tissue cells If the innate immune defense line is not broken by the virus, the immune response is up to this point, and the virus is also controlled On the contrary, if innate immunity cannot control the situation, acquired immunity must be activated Acquired immunity is mediated by T cells and B cells, which usually settle in lymph nodes and spleen The virus in the blood enters the spleen through blood circulation, mainly activating B cells and producing antibodies; the virus that invades the tissue will encounter the dendritic cells (a kind of important innate immune cells) in the tissue After the dendritic cells absorb the virus components, they enter the lymph nodes through the lymphatics at the tissue site, mainly activating T cells In addition to dendritic cells, virus particles themselves can also enter lymph nodes through lymphatics to activate B cells Once infected with novel coronavirus and other infections, once T cells and B cells are activated, their ability to exterminate viruses is extremely strong, and both show perfect synergy B cells become plasma cells after activation Plasma cells release a large number of antibodies that can recognize the virus The antibodies immediately enter the blood and interstitial fluid By combining with the virus, they can block the cells around them and enhance the phagocyte's phagocytosis of the virus The function of antibody is extensive, rapid and powerful, but the antibody can not enter into the cell For the virus that has entered into the cell, the antibody is powerless However, the virus can amplify a large number of new virus particles in the cell Once released, it may make the amount of local antibody relatively insufficient, and even some virus particles can avoid the blocking of antibody and infect the surrounding normal cells So all the antibodies do is stop the virus from entering the cell In fact, if the virus does not enter the cell, it will not cause damage to the body, and the virus outside the cell will automatically decay and decompose over time Therefore, eliminating the virus hidden in the cell is the biggest challenge facing the body or the immune system, and this arduous task is completed by T cells Different from the antibody released by B cells, T cells leave lymph nodes once activated (armed) and enter the site where the virus is located (going to the battlefield), where they recognize the infected and uninfected cells (distinguishing between enemy and me), and then selectively kill the infected cells (killing the enemy) As a result, during the death of infected cells, the virus in their cells was eliminated What happens after T cells and B cells clear the virus in the body? To answer this question, we need to find out what happened to T cells and B cells in the first place In lymph nodes and spleen, although there are many T cells and B cells, the number of T cells and B cells (immunologically called virus-specific T cells or B cells) that can truly recognize the virus is very small In order to deal with the dangerous virus invasion, these very few specific T and B cells need to be expanded in quantity when they are activated This expansion is very large For example, when a specific T cell is fully activated, 100000 identical T cells (immunologically called effector T cells) can be expanded When the effector T cells and B cells complete the task to clear the virus, more than 95% of the effector T cells and B cells will die rapidly, less than 5% of the cells can escape the fate of death, and survive in the body for several years, decades or even life, these cells are called memory T cells or memory B cells Memory is the core of the immune system, and it is the magic weapon for human beings to overcome various infectious diseases Generally speaking, immune memory refers to the first time t and B cells see the virus, how many years later when they meet the virus again, they can still recognize it at a glance Although we are not very clear about the process of immune memory formation, it has been known that the speed of memory response (the response of re contacting with virus T and B cells) is as fast as the innate immune response, so as to control the re invading virus rapidly Huang Bo said that no novel coronavirus epidemic in Wuhan is so serious, more and more infected people will recover from the state of the disease to the normal health state Due to the lack of specific antiviral drug intervention, this recovery basically depends on the immune cells of the body, especially the activated effector T cells and B cells Once the virus is controlled, the vast majority of these activated T cells and B cells will enter the death process, and only a few of them will survive and change into memory T cells and B cells, so as to protect the body from secondary sensation Dye Interestingly, antiviral antibodies can exist in the blood from several weeks to several years, which is caused by changes in B cells B cells do not produce antibodies themselves, but B cells can be converted into plasma cells after activation Antibodies are produced by plasma cells Plasma cells usually exist in lymph nodes, spleen and other parts, but in the process of transformation, B cells can also transform into a small number of long-lived plasma cells, which settle in the bone marrow and continuously secrete antibodies, which is the fundamental reason for the long-term existence of antiviral antibodies in the blood The body is novel coronavirus infection, once the immune memory is formed, memory T and B cells exist in the body for a long time They constantly monitor the initial infection of the coronavirus to invade again, preventing the two infection So, in the current severe situation of the epidemic, after the infected patients recover, will there never be a second infection? As the virus will mutate, secondary infection may occur, but the probability is very low Inheritance of novel coronavirus As like as two peas, RNA is a substance that is formed by linear polymerization of 4 nucleotides It spreads in the population and relies on RNA replication in cells (RNA produces a new RNA process exactly the same as that of RNA) However, RNA replication is not absolutely perfect, and there are errors in individual nucleotide sequence with low probability, which is the variation of virus There are four outcomes of virus mutation: (1) the mutation site is different from the site recognized by memory T and B cells, and the virus is still attacked by antibody and T cells, without secondary infection; (2) the mutation site occurs at the site recognized by antibody, but the antibody is invalid, but T cell monitoring exists, and there is no secondary infection; (3) the mutation site occurs at the site recognized by T cells, but the antibody is invalid Effective, no two times of infection; (4) the site of variation includes the site of antibody recognition and the site of T cell recognition, the antibody and T cell are invalid, the previously infected individuals can have two times of infection when contacting the virus with this variation In short, the novel coronavirus infected by Wuhan has recovered very well because of the low probability of occurrence of these fourth cases After recovering from the disease, it is shown that the body's immune system is normal, and then it is again infected with the virus There is usually no two infection In addition, when these patients are cured, the virus in their bodies should have been basically cleaned by antibodies and T cells At this time, the risk of infection of the patients themselves is greatly reduced, and they should not need isolation for 14 days after discharge If it is difficult to accept psychologically, the patient can be isolated for 2-3 days after discharge to further ensure that the patient is not infectious (BIOON Com)