On Feb 19th, the 10th day that a patient in Sichuan, China, had been cured and went home for isolation, the result of his RNA test was still positive. And this explosive news attracts people's attention and arouse their worries.
To this end, Huang Bo, Professor of Immunology Department of Peking Union Medical College, Chinese Academy of Medical Sciences and vice president of Chinese society of immunology, said: "Generally, there will be no secondary infection, which is mainly determined by the nature of the immune system and the location of the virus mutation. If the virus mutates, secondary infection may occur, but the probability is very low. "
The human immune system consists of two parts: the innate immune system and the acquired immune system. When the virus invades the body, macrophages in the innate immune system will quickly devour the invading virus. "There are two generals in acquired immunity - T cells and B cells, which are extremely powerful in killing viruses, and they show perfect synergy." Huang Bo.
When the acquired immune system is activated, B cells will immediately become plasma cells, releasing a large number of antibodies that can recognize the virus. These antibodies will immediately enter the blood and tissue fluid, by combining with the virus, blocking its infection of surrounding cells, while enhancing the phagocyte phagocytosis of the virus.
Although the function of the antibody is extensive, rapid, and powerful, it also has "weakness." Because it can't enter the cell, the antibody can't do anything for the virus that has entered the cell. Therefore, the biggest challenge is to eliminate the virus hidden in the cell, and this arduous task is completed by T cells.
Different from the principle of antibody release by B cells, once T cells are armed, they will leave the lymph nodes, and they will quickly identify the cells that have been infected by the virus, a fight against these cells, and the virus in the cells will be eliminated.
Interestingly, when T cells and B cells clear the virus, more than 95% of them will die quickly, and less than 5% of them can survive in the body for several years, decades, or even for life. These cells are called memory T cells or memory B cells.
"Generally speaking, when T cells and B cells meet the virus again, they can recognize it at a glance.". The speed of this memory response is as fast as the innate immune response, which can quickly control the re invading virus. "Huang Bo stressed that memory is the core of the immune system and the magic weapon for human beings to overcome various infectious diseases.
"In terms of new coronavirus, the recovery of many patients depends on the function of immune cells. Once the immune memory is formed, the memory T cells and B cells exist in the body for a long time, and the coronavirus that initially infected the body is always monitored for reinvasion to prevent secondary infection. "
In the process of transforming B cells into plasma cells, a small number of long-lived plasma cells can be transformed. They settle in the bone marrow and continuously secrete antibodies. These anti-virus antibodies can exist in the blood for weeks or even years.
The virus may mutate, but the probability of secondary infection is very low.
Generally, there will not be a secondary infection when recovered patients are exposed to the virus because these recovered patients have a normal immune system. In addition, when these patients are cured, the virus in their bodies should have been basically cleaned by antibodies and T cells, and their infectivity is greatly reduced. "Huang Bo said.
Currently, more and more novel coronavirus patients are recovering from hospital discharge.