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Scientists are learning more about how people respond to SARS-CoV-2, the new coronavirus responsible for the ongoing COVID-19 pandemic. Findings from a recent study suggest that prior exposure to “common cold” coronaviruses may generate the production of SARS-CoV-2 specific T cells.

SARS-CoV-2 belongs to the Coronaviridae family of RNA viruses. There are four coronaviruses known to circulate among the world’s population and transmit the “common cold.”

A healthy person’s response to a viral infection involves a coordinated effort between the innate and adaptive immune systems. Whereas the innate immune system — the first line of defense — involves barrier functions, such as those provided by the skin, the adaptive immune system includes distinct cell types that work together to neutralize the virus. T cells kill virus-infected cells and present viral fragments to B cells, which in turn produce antibodies against the virus. Some T cells, known as memory T cells, are long-lived and persist in the body to defend against future attacks by the same virus or related viruses.

Previous research on other viral infections has demonstrated that cross-reactive T cells circulating in a person’s blood may protect them from developing severe disease. The current study investigated the T cell response to the SARS-CoV-2 virus and explored the features of cross-reactive immunity.

The authors of the study examined blood collected from healthy people prior to the emergence of the SARS-CoV-2 virus. They detected CD4+ T cells in the blood of approximately half of the people unexposed to the SARS-CoV-2 virus. The authors speculate that these observations indicate the existence of cross-reactive immunity between SARS-CoV-2 and the coronaviruses that cause the “common cold.” They submit that this cross-reactivity may be a hopeful sign. However, it may also complicate COVID-19 vaccine trials if some subjects have pre-existing immunity.

These findings suggest that prior exposure to a related coronavirus stimulates the production of SARS-CoV-2 reactive T cells that persist in the body. Whether these T cells help an individual clear COVID-19 remains to be seen.

Learn more about COVID-19 in these Q&As featuring Dr. Rhonda Patrick, posted April 14 and June 10.

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