Ask Dr. Universe; The many parts of an immune system

Everyone who heard your question agreed that it’s a sophisticated one. To get my paws around the answer, I talked with my friend Phil Mixter. He’s an immunology professor at Washington State University.

He told me all living things need to protect themselves from microbes that could make them sick. These are called pathogens. They can be bacteria, viruses, fungi or parasites.

“Almost every organism I can think of — from plants to animals and beyond — has a defense system to handle the possibility that another organism might sneak in,” Mixter said.

Complex organisms need better defenses. That’s why animals like mammals have two-part immune systems.

The first part is called the innate immune system. It includes physical, chemical and cellular ways to keep pathogens out. It uses patterns to recognize something isn’t part of your body and eliminate it.

The second part is called the adaptive immune system. It includes those B cells and T cells you asked about. They’re both white blood cells called lymphocytes. They work as a team. B cells and T cells have different jobs on the protection team.

B cells produce and release proteins called antibodies. Their job is to grab onto pathogens and not let go. Sometimes the antibody blocks the part of the pathogen that interacts with your cells. These are called neutralizing antibodies.

Antibodies have another job, too. A pathogen with an antibody on it is marked for destruction. It’s like a giant neon X that tells your immune system to gobble up the pathogen or blast it with a chemical defense.

Mixter told me about two kinds of T cells: helper T cells and killer T cells. Helper T cells are in charge. They help B cells by telling them what to do — like what antibodies to make more of and where to send them. Killer T cells are like assassins. Their job is to look for pathogens hiding inside your cells. Then, they eliminate those unhealthy cells before they can spread.

Once the adaptive immune system encounters a pathogen, it’s primed to act if that pathogen shows up again.

“I like to think of it like a fire drill,” Mixter said. “The immune system is not the same after that first encounter.”

In real-life fire drills, you get faster every time you practice. The second time a pathogen shows up, the immune response is faster, too. Helper T cells can give the order to crank out B cells with the right antibodies. That’s called recall response. It’s more efficient to “recall” trained team members than to recruit and train new ones.

That’s also how vaccines work. When you get a shot, it trains your immune system to recognize a pathogen. Then the team, including B and T cells, is ready if the real pathogen comes along.

You’re a part of the team, too. The stuff you do to stay healthy — like getting shots and washing your hands — supports your immune system so it can protect you.

Have a science question? Ask Dr. Wendy Sue Universe, WSU’s resident science cat and writer, by email at Dr.Universe@wsu.edu, on her website at askDrUniverse.wsu.edu, via Twitter at @AskDrUniverse or at facebook.com/AskDrUniverse.