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.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.
The first time a virus infects the body, this response is sluggish; it takes several days for the immune system to sort out which T cells are best suited for the job at hand. But subsequent encounters typically prompt a response that is stronger and faster, thanks to a reserve force of T cells, called memory T cells, that lingers after the initial threat has passed and can quickly be called into action again.
In theory, cross-reactive T cells can “protect almost like a vaccine,” said Smita Iyer, an immunologist at the University of California, Davis, who is studying immune responses to the new coronavirus in primates. Previous studies have shown that cross-reactive T cells may guard people against different strains of the flu virus, and perhaps confer a trace of immunity against dengue and Zika viruses, which share a family tree.
Cross-reactive T cells alone probably would not be enough to completely stave off infection or disease. But they might alleviate symptoms of the coronavirus in people who happen to carry these cells, or extend the protection provided by a vaccine.But cross-reactive T cells are not necessarily a benevolent force. They could instead be ineffectual souvenirs of infections past, with “absolutely no relevance” to how well people fare against the new coronavirus.
T cells are also expert orchestrators. Depending on the signals they send out, they can synchronize cells and molecules from disparate parts of the immune system into a tag-teamed attack, or quell these assaults to return the body to baseline. If it turns out that cross-reactive T cells tend toward quieting the response, they could suppress a person’s immune defense before it has a chance to kick into gear, August said.
Then again, many types of T cells exist, and all operate as part of a complex immune system. “It’s almost like some people are trying to say this is ‘good’ or ‘bad.
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Source: Times of India
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