It is possible that people who recovered from the cold’s coronaviruses have T-cell memory against other coronaviruses, including the current one.
Coronavirus has a different impact for each person individually. For those who are asymptomatic or with mild symptoms may have the cell-mediated immunity they received from the simple cold, some of which cause the “harmless” HCoV virus.
They studied the phenomenon when a cellular immune response to SARS-CoV-2 is manifested in people who have not been infected with a new pathogen. However, their T cells reacted to certain regions of the novel coronavirus proteins in the same way as they did to the same regions of the common cold coronaviruses which are widespread and usually responsible for mild respiratory symptoms.
Neutralizing antibodies to HCoV are species-specific, that is, they do not respond to SARS-CoV-2, and one should not rely on cross-humoral immunity with them. That is why the strong variations in the course of coronavirus disease prompted scientists to believe that there is a T-cell memory of the coronavirus cold suffered in the past.
To know exactly whether the T-cell response to SARS-CoV-2 in non-sick COVID-19 is caused by HCoV in the past, scientists tested blood samples before 2019. Cells from there were “irritated” with fragments of SARS-CoV-2 proteins.
It turned out that the most powerful T-cell responses in non-ill Coronavirus were associated with those regions of the S-protein, thanks to which the new pathogen infects cells. Immune reactions have also been recorded to sites of other SARS-CoV-2 proteins. At the same time, the scientists clarified that the immune cells from the blood “until 2019” did not react to the membrane protein M, and T cells were detected in those who had had coronavirus.
Cross-reactive T-cell memory is present in about 20-50% of people. But scientists emphasize that it is false thought to believe that since you have had a coronavirus cold in the past, you do not care about a new infection.