Corona: cold antibodies can protect – Some antibodies against cold coronaviruses also respond to SARS-CoV-2



Protective pre-infections: A previous infection with a common cold coronavirus may provide at least partial protection against Covid-19, a study has now confirmed. Accordingly, antibodies remain in some people who also respond to SARS-CoV-2. Although these antibodies target other parts of the coronavirus than those newly formed with Covid-19, they can still inhibit the virus, the researchers report in the journal “Science”.

Doctors have long suspected that some people benefit from previous infections with one of four known cold coronaviruses. For example, in July 2020, a study showed that in some of these pre-infections, the immune system forms T helper cells, which can also respond to SARS-CoV-2. This cross-immunity, it was then believed, could explain the asymptomatic or mild course in some corona-infected people.

62 percent of the children already have antibodies

Now this suspicion is confirmed. Apparently there is such cross-immunity, not only in the cellular immune response, but also in antibodies, as Kevin Ng of the Francis Crick Institute in London and his colleagues discovered. For their study, they examined more than 300 blood samples from 2011 to 2018 – long before the corona pandemic – for antibodies that bind to SARS-CoV-2.

The researchers found what they were looking for: Some blood donors carried antibodies that recognized the new coronavirus – even though their immune systems never had contact with SARS-CoV-2. The proportion was low in adults; less than every tenth blood sample showed such antibodies. However, the proportion was significantly higher in children and adolescents: cross-reactive antibodies were found in 62 percent of the samples tested.

Does pre-immunity prevent the serious course?

“Our results show that children are more likely to carry such cross-reactive antibodies than adults,” says Ng. “This could explain why children are less likely to become seriously ill with Covid-19.” In children, infection with SARS-CoV-2 is disproportionately often asymptomatic or with only very mild symptoms. This is one of the reasons why many corona infections in children are not recognized, a recent Bavarian study found.

However, so far there is no evidence that these pre-existing antibodies completely prevent infection with SARS-CoV-2 or its transmission. However, along with already proven cellular pre-immunity, they could inhibit the multiplication of the coronavirus in some people and thereby prevent serious courses, the scientists suspect.

Cold coronaviruses as an origin

But where do these antibodies come from? Further tests showed that these immunoglobulins reacted strongly to one or more of the four known cold coronaviruses. According to the researchers, this suggests that these antibodies were originally raised against these cold viruses. Tests have shown that some surface structures of these viruses are similar to those of SARS-CoV-2. Antibodies against these common features therefore respond to both types of viruses.

However, the researchers found no evidence that a recent cold leaves more of such potentially cross-reactive antibodies than long ago. “People who have just gone through their first cold from coronaviruses should therefore not assume that they are now automatically immune to Covid-19,” Ng emphasizes.

Docked on S2 subunit

Further analyzes showed that the cross-reactive antibodies couple to the S2 subunit of the spike protein of SARS-CoV-2. This part of the “crowns” above helps the virus to enter the cell and changes only slightly between different coronaviruses. “Our study now shows that the S2 subunit between the common cold viruses and SARS-CoV-2 is similar enough for antibodies to work against both,” said Ng’s colleague George Kassiotis.

However, there are also clear differences: the antibodies formed in Covid-19 bind to both this S2 subunit and the S1 subunit, which is responsible for binding the virus to the cell. This has hitherto been considered the decisive starting point for blocking SARS-CoV-2 infection. But neutralization tests showed that the cross-reactive antibodies that only attach to S2 can prevent the virus from entering the cell.

“We now have good evidence that antibodies to S2 subunits can also be effective,” says Kassiotis.

Important for vaccines and the course of the pandemic

The new findings may provide important information for predicting the further course of the pandemic and vaccine development. Because if vaccines are applied to the less frequently altered subunit of the viral protein, they could also be more effective against various mutants of SARS-CoV-2.

“But it is important to emphasize that there are still some unanswered questions. For example, how immunity to one coronavirus changes through contact with another. Or why this cross immunity decreases so much with age, ”says Ng. He and his team have already begun a larger study to further investigate the role of various antibodies and other immune components in preimmunity and Covid-19 severity. (Science, 2020; doi: 10.1126 / science.abe1107)

Quelle: the Francis Crick Institute


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