An MD On How T-Cells Work & How To Tell If You’ve Had COVID

“Think of your immune system not as a black and white switch, but as an army of super soldiers,” he explains. “You’ve got your army, your Navy, your air force, the Marines. They all have their own weapons, they all have their own skill set.” 

In terms of what that looks like in your body, let’s break it down: The fluid in your nose, mouth, and even eyes are packed with antibodies, says Li, which act like a first line of defense when they come into contact with viruses. “These are called IgA,” says Li, or Immunoglobulin A. “They’ll block a lot of viruses and your body just sweeps them up and gets rid of them.” Example: When you blow your nose into a tissue, the viruses will get swept out along with your mucus. 

But if the virus manages to sneak its way in, other super soldiers must get to work: “And that’s not just the generic antibodies,” says Li. “It’s other parts of your innate immune system that have to look at the invader. They’ve got to conduct surveillance… They send some troops out to take a closer look at it. They size it up. They take a picture of it, and send it back to the home team to say, ‘You know what? This doesn’t look too good. I think we need to be able to mount a response.’”

Those soldiers—the ones who take snapshots of viruses who sneak past the first antibody system—are called T-cells. Says Li, whenever there’s a “bad guy” who managed to get past the first line of defense, your T-cells memorize the virus so they can flag it to other parts of your immune system when it needs to warrant a response. “They put it in the iCloud of your immune system,” he notes. 

If the virus builds up, your immune system will send killer cells to attack the threat—and once you’ve tackled the infection, those cells (the antibodies) will dial back down. “Your body won’t make any more antibodies unless it absolutely needs it,” says Li. “But the T-cells tend to stick around, because they’re always carrying around in their memory banks what that virus is.”