When I tell people I'm an immunologist, the most common responses I get are questions about vaccines or cold viruses. But did you know that your immune system is involved in nearly every disease and health maintenance process? Asthma, cancer, diabetes, eczema, multiple sclerosis, wound healing.... you name it. (Personally, I studied T cells in cancer and autoimmunity). Your immune cells are in nearly every little part of your body (except two "immune privileged" sites: the eyes and testes).
So what exactly is your immune system?
Your immune system is amazing army of "cells" that zoom around your body, waging attacks on suspected invaders and cleaning up the damage. It helps you get rid of invading viruses, bacteria, and parasites. It strives to eliminate cancerous cells. It helps you heal from cuts and scrapes.
Sometimes it gets a little too eager and attacks yourself ("autoimmunity" - a future post).
Let's back up for a second and talk about what a cell is. Cells are little building blocks that do a lot of listening, talking, and acting. Cells work together to achieve a larger goal. For example, the cells of your skin bind together to form a barrier to the outside world. Likewise, the cells of your immune system work together to keep you safe from invaders, cancer, and damage.
Let's introduce a few of these immune cell superheroes, as they are bound to pop up in stories to come...
B cells have little feelers ("receptors") on their surface. Each B cell has its own unique receptor, and there are millions of unique B cells in your body. Your body basically makes every possible variety of B cell so that there are little feelers looking out for any possible invader. Your body deletes any B cells that recognize your own personal body's building blocks (but sometimes this goes awry, resulting in autoimmune diseases... for another blog post).
When a B cell's receptor comes into contact with an invader (e.g., bacteria), the B cell becomes activated and starts telling the rest of the immune system superheroes that there's an emergency and it's time to spring to action. The B cell will make tons of copies of itself, and will unleash a ton of boomerangs ("antibodies") to surround the invader and facilitate cleanup by other immune system players. These antibodies are basically identical to the receptor, so they can bind the more of the same invader that was originally detected.
There are a few different types of T cells. Okay, there are like 20 different type of T cells. The running joke is that a new T cell type is discovered every year. But we'll be simple here and I'll tell you about three of them: 1) Helper T cells, 2) Cytotoxic T cells, and 3) Regulatory T cells.
Helper T cells are like members of a phone tree: they have a lot of messages to spread around when something's wrong. They don't attack or eat anything -- rather, they can sense when something's wrong and then tell others folks and help them do their thing.
Cytotoxic T cells are members of the frontline warriors. They throw toxic pellets at invaders.
Regulatory T cells tell everyone to stop. They help calm down the immune response, helping it to wind down.
Natural Killer cells go around checking to make sure you're still you. They have little feelers that shake hands with other feelers on your other cells all day. And should any of your cells be missing feelers, then they attack. Why would any of your cells be missing their feelers? Well, for example, cancer is sneaky and likes to try to hide from the immune system - it hides feelers that would give away its identity (for a future post!). Viruses also do this sometimes too. If a Natural Killer cell can't complete the handshake, it destroys the target cell.
Dendritic Cells go around eating everything in their environment, digesting them, and presenting them out on their cell surface for everyone else to see. Kind of like a toddler who shows you what they've just chewed up. But this is actually good manners, you see, because then other immune cells can come have a look and detect if there's an invader.
There are so many more superhero immune players, and we will meet them in upcoming posts. I showed this to my 2 year old and she said "Where are the monocytes??" So, for any other toddler critics out there, stay tuned!
How did all these immune cells come about?
They started out IN YOUR BONES! Ever hear of bone marrow? (Perhaps you've ordered it at a restaurant? Not me...) You have stem cells in your bone marrow and these give rise to all of your immune cells which then travel and take up residence all over your body, poised for action.
So, there's your brief introduction to the immune system. Upcoming topics include:
- How the immune system remembers (memory)
- Why you sometimes overcome an allergy, or develop a new one (tolerance)
- When the immune system mistakenly thinks you're an invader yourself (autoimmunity)
- How exactly the immune cell superheroes communicate
- Where do all the immune cells live? Where do they hang out?
Leave a comment if you have special topics / questions you'd like me to write up, simplify, and illustrate!
Angela
No comments:
Post a Comment