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A new study has suggested that asymptomatic individuals with COVID-19 mount an efficient T cell response that protects the host.
By analyzing blood samples from individuals infected with SARS-CoV-2, researchers have identified some of the differences in the body’s T cell responses that determine whether or not an individual develops COVID-19.
The study, conducted at Duke-NUS Medical School in Singapore, suggests that clearing the virus without developing symptoms requires T cells to build an effective immune response that produces a careful balance between pro and anti-inflammatory molecules. .
According to the researchers, what determines whether or not an infected individual develops symptoms remains unknown. Some studies have suggested that asymptomatic individuals produce less anti-SARS-CoV-2 antibodies than individuals who develop symptoms. However, it is not known whether their T cell responses are also reduced.
“Asymptomatic individuals constitute a variable but often large proportion of infected individuals and they should hold the key to understanding the immune response capable of controlling the virus without triggering pathological processes,” said Professor Antonio Bertoletti, one of the main researchers.
The team studied a group of migrant workers who were exposed to SARS-CoV-2 in April 2020. Over the course of six weeks, researchers regularly took blood samples from 85 workers who were infected but remained asymptomatic and compared their T cells to those of the 75 patients hospitalized for mild to moderate COVID-19.
The researchers found that, shortly after infection, the frequency of T cells recognizing SARS-CoV-2 was similar in asymptomatic individuals and COVID-19 patients.
However, T cells from asymptomatic individuals produced greater amounts of two proteins called IFN-γ and IL-2. These signaling proteins, or cytokines, help coordinate the immune system’s response to viruses and other pathogens.
As a result, researchers say the immune response to SARS-CoV-2 appears to be more coordinated in asymptomatic individuals. They challenged some of the blood samples with fragments of viral proteins and found that immune cells from asymptomatic individuals produce a balanced and well-proportioned mixture of pro and anti-inflammatory molecules. In contrast, the immune cells of COVID-19 patients produced a disproportionate amount of pro-inflammatory molecules.
“Overall, our study suggests that asymptomatic individuals infected with SARS-CoV-2 are not characterized by weak antiviral immunity; on the contrary, they mount a highly efficient and balanced antiviral cellular response that protects the host without causing apparent pathology, ”say the researchers.
The study was published in the Journal of Experimental Medicine (YWAM).
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