As Covid-19 rose five years ago, no one knew what to expect.
Or the immune system.
In front of a new virus, humanity was immunologically naive. The appearance of SARS-COV-2 made imaginable examine the immune formula in action, and the researchers ran to gather all the knowledge they could. “The global has been exposed to a new pathogen of the logo,” said Nadia Roan, an immunologist at the University of California in San Francisco. “We were looking to take the merit of this to be informed more about immunity. “
Years later, scientists are still passing on knowledge to awaken a greater functioning of the immune system. Here are 4 classes they have learned so far.
At the beginning of the pandemic, many researchers pointed to antibodies produced in reaction to SARS-CoV-2 infection. Antibuerpos similar to Example, have analyzed the levels of antibodies, T cells.
That’s in part because T cells are more difficult to study than antibodies, and so our understanding of them has lagged, says Shane Crotty, an immunologist at the La Jolla Institute for Immunology in San Diego, California.
As the pandemic went on, however, it became clear that T cells were a crucial arm of the immune response to SARS-CoV-2 and to COVID-19 vaccines, says Alessandro Sette, also an immunologist at the La Jolla Institute for Immunology. Antibodies against SARS-CoV-2 waned in the months after vaccination, but vaccinated people continued to make T cells that recognized the virus1. That T-cell protection remained strong, Sette and others found2, even against viral variants that dodged the antibody defences raised by the first generation of COVID vaccines.
“People used to focus more on antibodies, and tended to forget about the T-cell responses,” says Rosemary Boyton, an immunologist at Imperial College London. “Now we understand much, much better that the T-cell responses matter as well.”
The pandemic also gave researchers new insights into the innate immune system, another line of defence against viruses.
Innate immune reactions are not as express as antibodies and T-mobiles. Cells can release those reactions when they stumble upon foreign molecules, such as the SARS-CoV-2 RNA genome. When a mobile phone discovers a telltale molecule, it raises the alarm, by releasing proteins called interferons. These proteins activate gene loads, many of which are concerned with viral defense. The interferon reaction also warns that other cells in the same organ are on higher alert, explains Benjamin Tenoever, a virologist at New York University in New York. “It can be very overwhelming for a virus. “
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Before the pandemic, researchers thought that this warning cry did not travel far beyond the site of infection. But when tenOever and his colleagues analysed samples from hamsters and from autopsies of people who had previously been infected with SARS-CoV-2, they found signs of interferon responses throughout the body, even in organs far away from infected cells3. Later, the team learnt that this is not limited to SARS-CoV-2: the flu virus also elicits a widespread interferon response in hamsters.
Tipoever hypothesizes that these global antiviral defenses charge in case the infection temporarily moves through the body. This may also be a component of the explanation why SARS-Cov-2 variants that spread later in the pandemic were less likely than their predecessors to cause severe disease — the following variants connected more than the virus’s previous bureaucracy Nose cells, keep the virus in the upper respiratory tract longer. This allowed the innate warning signal to be successful in the lungs and defenses before the arrival of the virus.
Before the pandemic, the researchers were not very interested in the nose, explains José Ordovas-Montans, immunologist at Boston’s Children’s Hospital in Massachusetts. “He thought as an undeniable passive tube to take the air to the lungs,” he said. “And the lungs were the position where the company occurred. “
Pandemia has highlighted the importance of understanding immune responses in express tissues, and especially where infection begins: nose.
The rainy lining of the nose is an immune environment unique to a combination of antibodies and immune cells that is discovered in the blood. As a result, injected vaccines, which generate antibodies in the bloodstream, may not be ideal for blocking infection in the nose. “One of the kinds of the pandemic is location, location, location,” Crotty says.
DOI: https://doi. org/10. 1038/d41586-025-00128-w