The scientists revealed that there are people whose organisms are immune to the new coronavirus without having the antibodies that appear after contracting the disease.
For several months the new coronavirus has been the focus of research for scientists around the world. Among other topics, it was studied why some people are immune to COVID-19 and why the course of the disease differs between several patients.
Immune system prepared
Dutch scientists discovered that even those who have never had COVID-19 can have immunity against its pathogen.
Biologists have analyzed human monoclonal antibodies 47D11 obtained during an epidemic of the severe acute respiratory syndrome, the so-called atypical pneumonia. The SARS-CoV virus that causes it resembles the pathogen causing COVID-19.
These antibodies introduced into the infected cells successfully neutralized the viral particles. The authors have suggested that they can protect healthy people from infection, and help patients cope with the virus.
Another international team of scientists led by Swiss virologist Dora Pinto discovered similar antibodies.
In the body of a patient who overcame atypical pneumonia in 2003, 25 antibodies were found, but only one neutralized the new coronavirus. On the surface of the viral particle, it detected an area of protein S, characteristic of both pathogens, that binds to it and prevents SARS-CoV-2 from entering the cell.
The memory of cells
The German researchers revealed that sometimes it is not the antibodies that protect against the coronavirus – but the T lymphocytes, which provide cellular immunity.
In this case, macrophages eat the pathogen, and fragments of its proteins are placed on the membrane. In turn, they are recognized by T cells with the help of special receptors that, like antibodies, bind to immunoglobulins and specifically bind to antigens. In this way, the immune response develops.
It turned out that some T cells already know how to respond to SARS-CoV-2. This is why some people tolerate COVID-19 more easily or are completely asymptomatic.
The scientists found that 30% of healthy volunteers had T cells that responded to protein S from a dangerous pathogen. Most often, these cells recognized those fragments that were similar to the protein S parts of other coronaviruses, for example, that cause a common cold HCoV-229E. Also, these people had antibodies against this type of virus in their blood.
Additionally, T cells responding to SARS-CoV-2 were found in most patients with COVID-19. Those without them tended to become more seriously ill.
The scientists concluded that people who have previously contracted seasonal coronaviruses are already immune to COVID-19.
Immunity after illness
American scientists verified the conclusions of their German colleagues.
The researchers analyzed blood samples taken from patients from 2015 to 2018, that is when COVID-19 was not yet known. Almost all biological materials showed signs of specific cellular immunity similar to those found in SARS-CoV-2 infection.
They are two types of immune cells: cytotoxic T lymphocytes (CD8 cells) and helper T lymphocytes (CD4 cells). The former recognize cells affected by viruses and destroy them. The latter increases the number of cytotoxic T lymphocytes and improve their response to a specific pathogen.
Almost half of the samples taken three to five years ago had the specific CD4 cells that are now common to people with COVID-19. Furthermore, 20% of them also had CD8 cells, which are found in 70% of patients with new coronaviruses. So almost half of the world’s healthy population may be immune to the new disease, the authors note.
A further study of blood samples obtained in the years 2015-2018, showed antibodies against the two most famous coronaviruses that affect humans, HcoV-OC43 and HcoV-NL63. In other words, people who had previously contracted other coronavirus infections became immune to SARS-CoV-2. This is probably the explanation for asymptomatic COVID-19, they suggest.