One of them died of COVID, and all four needed to be put on ventilators in an intensive-care unit. But their specific mutation is not common, and genetics are unlikely to completely explain the variation in COVID cases. Every scientist I spoke with emphasized how little we know. The asymptomatic end of the severity spectrum is the most difficult to study. The first challenge is finding the cases: Asymptomatic people do not come to the hospital and are unlikely to get tested.
If they are tested, their early immune response is typically long over by the time results come back. Finding asymptomatic patients usually means following a large group of healthy people for a long time, waiting for some of them to catch the virus of interest. Although Singapore had so far largely controlled the spread of COVID, an outbreak was raging among its migrant workers, many of whom were from India and Bangladesh.
To contain the outbreak, the government paid the workers to isolate at home and track their symptoms with thermometers and oximeters. During the isolation period, Bertoletti and his colleagues recruited workers who were willing to have their immune responses tracked through periodic blood samples. A large majority of cases were asymptomatic, and the rest were mostly mild.
Bertoletti and his colleagues were interested in virus-specific T cells that are essential to the adaptive-immune response. When they isolated these cells from blood samples, they found that asymptomatic patients had more specific and coordinated T-cell responses with high levels of an antiviral molecule and another that regulates other T cells. T cells may play an additional role in milder infections: Depending on where in the world you look, some 28 to 50 percent of people have T cells that predate the pandemic but nevertheless react to the new virus.
These T cells may be remnants of infections with related coronaviruses, a theory supported by one study, which found that people who were more recently infected by other coronaviruses tended to have milder COVID infections.
To further understand the role of cross-reactive T cells, Sette, at La Jolla, is studying whether patients who possess them also mount a stronger immune response after receiving a COVID vaccine.
T cell responses also weaken with age, which may help explain why COVID is dramatically more deadly for the elderly. Humans have a huge diversity of T cells, some of which are activated each time we encounter a pathogen.
But as we age, our supply of unactivated T cells dwindles. Viruses are extremely tiny parasites made of genetic material, wrapped in proteins and sometimes an outer membrane layer, which hijack living cells to reproduce themselves.
The first stages of an infection happen when a virus gets past our physical barriers of skin and mucus, and enters a suitable cell. Once inside, a virus can take over the cell, forcing the cell to make many copies of the virus replicate , which damages the cell and sometimes kills it. The newly-made viruses are released to find a new cell.
A British doctor is often credited with the first vaccine for smallpox in the s, but a Chinese emperor who was a smallpox survivor himself started an inoculation program against the disease in the mids. Now that you've learned a little bit about your immune system, find out how it's used to fight cancer. Part 2 of this article explains how cancer cells turn off the immune response and how immunotherapy seeks to turn it back on.
Return to homepage. Pictured: To stay healthy, wash your hands frequently and stay away from this guy. Friday, September 21, - am. This is the first of two articles about how your immune system works. Learn More. Activating Your Immune System Against Cancer Now that you've learned a little bit about your immune system, find out how it's used to fight cancer.
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