Memory T cells may only reduce COVID-19 severity

#GS3 #Science #Biology 

At least six papers published in reputable journals — Cell, Nature, Science, and Science Immunology — have found that 20-50% of people who have not been infected with the novel coronavirus (SARS-CoV-2) harbor memory T cells derived from previous exposures to common cold coronaviruses. The memory T cells were found to cross-react with SARS-CoV-2.

Reduce disease severity

  • “Pre-existing T cell immunity to SARS-CoV-2 could be relevant because it could influence COVID-19 disease severity. 

Unlikely to prevent

  • “The memory T cells are extremely unlikely to prevent SARS-CoV-2 infections. That is just not what T cells generally do. 

Killer T cells

  • The cross-reactive memory T cells on activation would help in the development of plasma cells and thus antibody production and in the development of killer T cells that would kill virus-infected cells. The latter reduces the reservoirs of infection. This would most likely reduce disease severity.

Herd immunity

  • A few researchers have also been mistaking pre-existing cross-reactive memory T cells to be playing a part in achieving herd immunity even when only a small percentage of the population is infected.
  • In a bid to clear the misconception regarding cross-reactive memory T cells and herd immunity, Prof. Crotty commented that “there are various tweets misinterpreting COVID-19 ‘pre-existing immunity’ and making dangerous claims about herd immunity”. He says cross-reactive immune memory, which avoids the word immunity, may sometimes get misinterpreted as “protective immunity”.
  • Dismissing the possibility of cross-reactive memory T cells producing herd immunity when only a small percentage of the population is infected.
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