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, says Annika Karlsson, an immunologist at the Karolinska Institute in Stockholm. “If they are able to kill the virus-infected cells before they spread from the upper respiratory tract, it will influence how sick you feel,” she says. They could also reduce transmission by restricting the amount of virus circulating in an infected person, meaning that the person sheds fewer virus particles into the community.
T cells could also be more resistant than antibodies to threats posed by emerging variants. Studies by Sette and his colleagues have shown that people who have been infected with SARS-CoV-2 typically generate T cells that target at least 15–20 different fragments of coronavirus proteins1. But which protein snippets are used as targets can vary widely from person to person, meaning that a population will generate a large variety of T cells that could snare a virus. “That makes it very hard for the virus to mutate to escape cell recognition,” says Sette, “unlike the situation for antibodies.”
Author(s): Heidi Ledford
Publication Date: 12 February 2021
Publication Site: nature