Some unexposed people may have COVID-19 immunity

bdmetronews Desk ॥ Eight months ago, the new coronavirus was unknown. But to some of our immune cells, the virus was already something of a familiar foe.

A flurry of recent studies has revealed that a large proportion of the population — 20% to 50% of people in some places — might harbor immunity assassins called T cells that recognize the new coronavirus despite having never encountered it before.

These T cells, which lurked in the bloodstreams of people long before the pandemic began, are most likely stragglers from past scuffles with other, related coronaviruses, including four that frequently cause common colds. It’s a case of family resemblance: In the eyes of the immune system, germs with common roots can look alike, such that when a cousin comes to call, the body may already have an inkling of its intentions.

The presence of these T cells has intrigued experts, who said it was too soon to tell whether the cells would play a helpful, harmful or entirely negligible role in the world’s fight against the current coronavirus. But should these so-called cross-reactive T cells exert even a modest influence on the body’s immune response to the new coronavirus, they might make the disease milder — and perhaps partly explain why some people who catch the germ become very sick, while others are dealt only a glancing blow.

“If you have a population of T cells that are armed and ready to protect you, you could control the infection better than someone who doesn’t have those cross-reactive cells,” said Marion Pepper, an immunologist at the University of Washington who is studying the immune responses of COVID-19 patients. “That’s what we’re all hoping for.”

T cells are an exceptionally picky bunch. Each spends the entirety of its life waiting for a very specific trigger, like a hunk of a dangerous virus. Once that switch is flipped, the T cell will clone itself into an army of specialized soldiers, all with their sights set on the same target. Some T cells are microscopic assassins, tailor-made to home in on and destroy infected cells; others coax immune cells called B cells into producing virus-attacking antibodies.

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