Central idea: The SARS-CoV-2 virus has the ability to evade CD8 T cells, which are important in reducing the viral load and clearing the infection by detecting and killing infected cells.

What is the news?

• A recent study has revealed that the SARS-CoV-2 virus has the ability to modulate MHC I expression in host cells.
• MHC I is crucial in alerting the immune system to virally infected cells.
• The virus has evolved multiple strategies to inhibit MHC I expression, which is not seen in the case of the influenza virus.

What is T Cell Immunity?

• Like B cells, which produce antibodies, T cells are central players in the immune response to viral infection.
• For your immune system to fight off any kind of invader, such as a virus, you need a kind of white blood cell called a B cell, which makes antibodies, and a similar-looking white blood cell called a T cell.
• T cells can play different roles altogether.
• They can act as “killer cells”, attacking cells which have been infected with a virus or another kind of pathogen, or they can act as “helper cells” by supporting B cells to produce antibodies.

How do they function?

• Alongside antibodies, the immune system produces a battalion of T cells that can target viruses.
• Some of these, known as killer T cells (or CD8⁺T cells), seek out and destroy cells that are infected with the virus.
• Others, called helper T cells (or CD4⁺T cells) are important for various immune functions, including stimulating the production of antibodies and killer T cells.
• T cells do not prevent infection, because they kick into action only after a virus has infiltrated the body. But they are important for clearing an infection that has already started.
• In the case of COVID-19, killer T cells could mean the difference between a mild infection and a severe one that requires hospital treatment.

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