T Cells Crucial in Avoiding Symptoms of COVID-19

Cells reactive to SARS-CoV-2 peptide pools were found in all anti-NP IgG–positive individuals.

Recent data published in the Journal of Experimental Medicine has suggested that T cells are a key component in clearing the COVID-19 virus without developing any symptoms. An efficient response can produce a careful balance of pro and anti-inflammatory molecules. The study was conducted by the Saw Swee Hock School of Public Health in Singapore, in collaboration with the National University of Singapore and the National Research Foundation of Singapore.

An infection with SARS-CoV-2 triggers an immune response by antibodies and T cells that recognize the virus and attempt to clear it from the body. However, this response sometimes causes an excessive amount of inflammation that can damage tissue and worsen symptoms.

It is still unknown what determines someone who is infected from showing symptoms, though some studies have suggested those who are symptomatic produce fewer anti-SARS-CoV-2 antibodies than those with symptoms.

"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," Antonio Bertoletti, a professor at the Duke-NUS Medical School in Singapore said.

Investigators behind the study analyzed a group of migrant workers who were exposed to COVID-19 over the course of 6 weeks/ They took blood samples from 85 who became infected and were asymptomatic and compared them to 75 who were hospitalized with a mild to moderate case of the disease.

Findings showed that shortly after the infection, the frequency with which the T cells recognized the virus was similar in both groups. However, the T cells of the asymptomatic group produced a greater amount of two types of proteins called IFN-γ and IL-2. The 2 proteins help coordinate the response of the immune system when there is a virus or pathogen present. Additionally, the asymptomatic group showed a balanced, well-proportioned mix of pro and anti-inflammatory molecules, while the other group had a disproportionate amount of proinflammatory molecules.

"Overall, our study suggests that asymptomatic SARS-CoV-2-infected individuals are not characterized by a weak antiviral immunity; on the contrary, they mount a highly efficient and balanced anti-viral cellular response that protects the host without causing any apparent pathology," the investigators said.