Whenever an immune cell encounters a trespasser, it slots into it like a key into a lock, holds on tight, and sounds the alarm. That's what happens if a flu virus enters your body. As soon as your immune sentries raise the alarm, the troops swing into action.
First, T cells start reproducing in order to outnumber the virus. Each new T cell is programmed to fight this exact enemy. Some of these cells, the "natural killer" (NK) cells, surround the cells where the invading virus has hidden. NK cells attack your virus-contaminated cells, in a sense suffocating them. They release deadly chemicals that make the cells burst.
Now chemical messengers are sent to summon aid for your body's first line of defense. As these chemicals concentrate at the site, the area begins to redden, swell, and get tender. These are the signs of an infection. The same reaction creates the muscular and joint aches you feel when you are sick. Some of the chemicals released signal the brain to raise the body's temperature to make the immune cells work faster—and so you run a fever.
Now you feel the familiar "swollen glands." These really aren't glands at all, but collection points along the network of tubes that transport the immune cells pouring forth to fight the invader. The tube system is called the lymph system, and the collection points are lymph nodes. When they get large and tender, that means battalions of immune cells are mustering for battle. Rather than a sign for alarm, such an inflammation shows that the body is doing its normal job, and that a ferocious battle is raging within.
By now, the invaders are probably wondering how they ever got into this mess as they are outnumbered by attacking T cells and surrounded by blood chemicals helping those cells. What else could go wrong?
I'm glad you asked. Because right about now your immune troops bring on a new weapon: the antibodies. Antibodies are tuned like guided missiles to hone in on the invader, and thousands of them pour into the bloodstream every second. They zoom in, surround the virus and hold on for dear life. (You'll be hearing more about antibodies, too, because if your body lacks certain nutrients, it won't do a very good job of making the antibody "missiles" you need.)
Enter the last fighter in the immune battle, the macrophages, another kind of white blood cell. Their name means, literally, "big eater," and that's exactly what they do. Whenever they see something covered with antibody—that is, an invader—they lumber up and "eat" it.
With so many immune defenders at work, the virus doesn't have a chance. It is ganged up on by T cells, antibodies, macrophages, and all the blood chemicals that the immune system recruits. With all this tumult going on inside you, it's no wonder you feel so tired when you get the flu! |
