SARS-CoV-2 immunity can last for more than 6 months due to antibody evolution and B cell memory

The 2019 coronavirus disease (COVID-19) pandemic has infected more than 52.7 million people worldwide and killed more than 1.2 million people, resulting in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-). 2), a pathogen that causes COVID-19.

Research team from Howard Hughes Medical Institute, USA has studied the evolution of antibodies to combat SARS-CoV-2 infection.Their study “Evolution of antibody immunity against SARS-CoV-2” has been released on the preprint server bioRxiv*.

Background

SARS-CoV-2 infection causes the development of antibodies that can neutralize viral antigens. Spike protein What the virus uses to invade host cells. Therefore, they protect individuals from reinfection. It can be seen that the levels of antibodies developed against infection can vary from person to person, and that antibody levels also decline over time. However, there are certain types of B cells in the immune system called memory B cells. Researchers suggest that these memory B cells may be “required to produce antibodies upon reinfection.” This type of immune response is called the humoral memory response.

The team explains that their robustness in the use of this memory B cell and the prevention of reinfection has not yet been investigated.

Study design

In this study, the research team examined humoral memory responses in 87 people. The humoral antibody response of participants was studied 1.3 and 6.2 months after SARS-CoV-2 infection. Nussenzweig, an immunologist at Rockefeller University in New York City and a contributor to the research project, explains: “Our idea is if we can find something like that Neutralizing antibody, Find out which part of the virus vaccine you need to target. “

Survey results

Overall, the results of the survey are as follows:

Antibodies decrease over time

• The antibody response to SARS-CoV-2 was found approximately 1.3 months or 40 days after infection.
• IgM, IgG and IgA anti-RBD (receptor binding domain) antibodies in plasma decreased 1.3-6.2 months after recovery from infection
• Antibody type IgM showed the greatest reduction in anti-RBD reactivity (53%), followed by IgG (33%), but IgA was reduced by only 15%.
• Patients with prolonged symptoms had significantly higher anti-RBD IgG and anti-N antibody levels at both time points
• Antibodies to RBD and plasma neutralizing activity were significantly reduced, but were detectable in most patients 6.2 months after infection.

Memory B cells

• Plasma antibody levels declined over time, but memory B cells were found to contribute to the immune response late after recovery.
• To this end, the team used flow cytometry to isolate B cells containing receptors that bind to RBD.
• Memory B cells bound to RBD increased significantly between 1.3 and 6.2 months
• The authors conclude that “the size of the RBD-specific memory B cell compartment is conserved 1.3-6.2 months after SARS-CoV-2 infection, but there is significant evolution of clone turnover and antibody sequences. I’m attaching … “

Evolution of antibodies

• Antibody evolution is caused by mutations in the germinal center. Here, antigens from the virus are retained in the form of immune complexes.These antigen-antibody complexes have long been present on the surface of follicular dendritic cells.
• The virus that remains in the body after recovery acts as a source of viral antigens for the generation of antibodies. The team discovered that they could be in the intestines.
• Computed tomography and other methods have helped find these residual viruses.
• The team said mutations in antibodies produced early after recovery from infection were low.
• The team writes, “The response of anti-SARS-CoV-2 memory B cells evolves during the first 6 months after infection …”.

Circos plot and IgG-positive RBD-specific B cells a, sequences from all 6 individuals with clonal relationships drawn. The interconnect line shows the relationship between antibodies that share the V and J gene segment sequences in both IGH and IGL. The purple, green, and gray lines interconnect the associated clones, clones and singles, and singles, respectively. b, For each patient, the number of IgG heavy chain sequences (black) analyzed from 6 individuals 694 1.3 months (left panel) or 6.2 months (right panel) after infection. The numbers in the inner circle indicate the number of cells sorted by individual shown above the circle. Same as c and b, but showing combined data for all 6 patients. d, Comparison of the proportions of 6 IgG-positive B cells 1.3 or 6.2 months after infection. The horizontal bar indicates the average. Statistical significance was determined using the paired t-test.

Conclusions and implications

Researchers have found that “memory responses are responsible for protection from reinfection and are essential for effective vaccination.” This evolution of memory B cells occurs between 1.3 and 6.2 months after infection. Antibodies continue to evolve due to the persistent presence of the antigen in the form of residual virus.

“The really good news is that infected people are very unlikely to get sick again for at least six months,” Nussenzweig said in a statement. “Our results show that it is not difficult for our immune system to produce effective antibodies against SARS-CoV-2,” said Christian Gabler, another researcher on the project. Said.He was also talking about their previous work published in the journal Nature, June this year (2020).

“One of the things people are very worried about is what happens in 6 months or a year,” said Nussenzweig. “Will individuals who have recovered from COVID-19 still be protected?” This study found that the answer could be “yes”, especially for people with persistent viruses in their bodies, especially in the intestines. It does, the researchers say.

*Important Notices

bioRxiv Publish preliminary scientific reports that should not be considered definitive as they are not peer-reviewed, guide clinical / health-related behaviors, and should not be treated as established information.