Colored scanning electron micrograph of a cell (blue) that is heavily infected with SARS-CoV-2 virus particles (red) and that was isolated from a patient sample. Image taken at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Image Credit: NIAID
Mild cases of coronavirus disease 2019 (COVID-19) can trigger robust memory T-cell responses, even when there are no detectable virus-specific antibody responses, researchers report on August 14 in the journal Cell. The authors say that memory T cell responses produced by natural exposure to, or infection with, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) – the virus that causes COVID-19 – have a significant immune component Can be used to prevent recurring severe episodes of illness.
"We are currently facing the biggest global health emergency in decades," says lead author Marcus Buggert of the Karolinska Institutet. "In the absence of a protective vaccine, it is important to determine whether exposed or infected individuals, particularly those with asymptomatic or very mild forms of the disease who are likely to inadvertently act as primary transmitters, develop robust adaptive immune responses to SARS-CoV." 2. "
So far, there is limited evidence of reinfection in humans with previously documented COVID-19. Most studies of immune protection against SARS-CoV-2 in humans have focused on the induction of neutralizing antibodies. However, antibody responses tend to decrease and are not detectable in all patients, especially those with less severe forms of COVID-19. Studies in mice have shown that vaccine-induced memory T-cell reactions, which can last for many years, protect against the related virus SARS-CoV-1 even in the absence of detectable antibodies. So far, it has not been clear how SARS-CoV-2-specific T cell responses are related to antibody responses or the clinical course of COVID-19 in humans.
To fill this knowledge gap, Buggert and his colleagues examined SARS-CoV-2-specific T-cell and antibody responses in more than 200 people from Sweden across the spectrum of exposure, infection and disease. During the acute phase of infection, the T cell responses were associated with various clinical markers of disease severity. After recovery from COVID-19, SARS-CoV-2 specific storage T cell responses were detectable. The strongest T cell responses were in those who recovered from severe COVID-19. Meanwhile, people who recovered from very mild COVID-19 and family members exposed to the virus have seen progressively lower T cell responses.
As expected, all 23 people who recovered from severe COVID-19 developed both SARS-CoV-2 specific antibody and T cell responses. Surprisingly, SARS-CoV-2 specific memory T cell responses were seen months after infection in exposed family members and in most individuals with a history of very mild COVID-19, sometimes in the absence of SARS-CoV-2 specific Antibodies. Of the 28 exposed family members, only 17 (some more than half) showed detectable antibody responses, while almost all (26/28) showed T cell responses. Of the 31 people who recovered from mild COVID-19, almost all had detectable antibody responses (27/31) and developed T cell responses (30/31).
"Our results suggest that the dependence on antibody responses may underestimate the level of population-level immunity to SARS-CoV-2," says Buggert. "The obvious next step is to determine whether robust memory T-cell responses in the absence of detectable antibodies can protect against COVID-19 over the long term."
The experimental COVID-19 vaccine protects the upper and lower respiratory tract in non-human primates
Takuya Sekine et al., Robust T-Cell Immunity in Convalescents with Asymptomatic or Mild COVID-19, Cell (2020). DOI: 10.1016 / j.cell.2020.08.017
Mild COVID-19 Cases May Produce Strong T Cell Response (2020, Aug 17)
accessed on August 17, 2020
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