As reported, the study results on immunity to SARS-Cov-2 from previous infections with other coronaviruses are now piling up. A study headed by the Charité – Universitätsmedizin Berlin and the Max Planck Institute for Molecular Genetics (MPIMG) is now doing this. Immune cells were found in healthy people, which can also recognize SARS-CoV-2. The reason is suspected in previous infections with common cold coronaviruses. Another study is now to show how the protection affects the course of an infection with SARS-CoV-2.

British researchers recently published a study that showed 62 percent of non-infected children in the 6 to 18 age group had immunity to SARS-Cov-2 in one study. Not only were T cells found, but also neutralizing IgG antibodies.

The low infection rate and low mortality in Southeast Asia – there have been no deaths in Vietnam, Laos and Cambodia – is attributed to frequent infections with SARS-like coronaviruses. According to research, there are said to be around 100 other corona viruses.

Relationship of the corona viruses

The German study, now published in Nature, also pursued the question of why it is that some people are seriously ill with the coronavirus, while others hardly notice any symptoms. A research team from the Charité and MPIMG has now also identified a possible influencing factor: previous infections with harmless cold coronaviruses.

This is indicated by studies on so-called T helper cells – specialized white blood cells that are essential for controlling the immune response. As the scientists observed, about a third of people who have never come into contact with SARS-CoV-2 have T-helper memory cells that still recognize the new virus. The reason for this is probably that SARS-CoV-2 is not so “new” after all and that certain structures are similar enough to the common corona viruses to be recognized.

The results

For their investigations, the researchers obtained immune cells from the blood of 18 COVID-19 sufferers who had been admitted to the Charité for treatment and tested positive for SARS-CoV-2 using a PCR test. In addition, they isolated immune cells from the blood of 68 healthy people who had never been shown to come into contact with the new corona virus.

The immune cells then stimulated them with small, artificially produced fragments of the so-called spike protein from SARS-CoV-2. It is typical of the surface of the corona viruses and enables them to enter human cells. The research group then checked whether the T-helper cells had been activated by the protein fragments. The result: In 15 of the 18 COVID-19 sufferers, i.e. 85 percent, the T helper cells reacted to the fragments of the virus surface.

“We didn’t expect otherwise, the patient’s immune system was fighting the new virus and therefore reacted to it in a test tube,” explains Dr. Claudia Giesecke-Thiel, head of the flow cytometry service group at the MPIMG and one of the three leading authors of the study. “The fact that the T helper cells did not react to the virus fragments in all COVID-19 sufferers is probably due to the fact that the T cells cannot be activated outside the body in an acute or particularly severe stage of a disease.”

Immune defense against SARS-Cov-2 in those not infected with it

To the team’s surprise, reactive T helper cells were also found in the blood of healthy people: 24 of the 68 tested (35 percent) had memory cells that recognized SARS-CoV-2 fragments. The scientists noticed that the immune cells of COVID-19 sufferers and healthy people reacted to different sections of the virus envelope. The British study also showed that.

While the patient’s T helper cells recognized the full length of the spike protein, the healthy T helper cells were activated primarily by sections of the spike protein that resemble corresponding sections of the spike protein by more harmless cold coronaviruses.

“This suggests that the healthy T-helper cells react to SARS-CoV-2 because they had to deal with local cold coronaviruses in the past,” says Giesecke-Thiel. “Because one property of the T helper cells is that they can not only be activated by an exactly ‘suitable’ pathogen, but also by ‘sufficiently similar’ intruders.” In fact, the research group was able to demonstrate that the T helper cells of healthy volunteers, who reacted to SARS-CoV-2, were also activated by various cold coronaviruses – and thus by definition “cross-reacted”.

In order to conclusively clarify whether previous coronavirus colds actually protect against later infection with SARS-CoV-2 – and thus possibly explain the different manifestations of the symptoms – future-oriented studies are necessary. One such study – the Charité Corona Cross study – has now started under the direction of the Charité in cooperation with the Technical University of Berlin and the MPIMG.

Corona viruses cause up to 30 percent of seasonal colds in Germany. It is estimated that on average an adult gets infected with one of the four domestic corona viruses every two to three years.

Immunity in children through antibodies from corona cold viruses is strongly expressed with up to 60 percent

A common cold can make you immune to the corona virus

Corona puzzle Asia – few infections and few deaths thanks to widespread immunity

Coronavirus T cells provide longer immunity than antibodies