I'd like to talk to you today about dendritic cells. Dendritic cells are one of the key elements of the immune system. They've been discovered over 150 years ago, but only in the past 10 years, that we've really started to understand their crucial role in the immunity. Um, they are actually named after, uh, what they looked like not after what they did. Den dry are long extensions from the cell. And that's what dendritic cells look like. They're found in practically all tissues, which means they're important, especially in the lining of the lung and the gut. And as you can imagine, as you're breathing in air with a possible invader, just certain pathogens or you're eating food that could have bacteria and other viruses, um, it's important that the body has a way to recognize that there's an invader, uh, and try to fight it off using the immune system.
Now, there's something interesting about dendritic cells and why are they so important on the outside of the dendritic cell? They're actually decorated with proteins that are called toll receptors and what that is, are proteins that can recognize patterns from pathogens. In other words, viruses have certain types of, um, RNA or DNA or proteins and bacteria have certain kinds of lipid and fat and, and back in DNA. And, uh, these total receptors can specifically recognize that type of molecule. And when it recognizes that it triggers the dendritic cell to actually ingest the path that Jen or the cancer cell, for example, and what it does then is it digested into little pieces and put certain fragments back on its surface. It basically displays them like a flag. And at that time, the dendritic cell changes its mission. It says, okay, I know there's an invader. So then it does undergo something called maturation.
It moves to the lymph nodes where it engages with T cells. The T cells are there waiting. And the dendritic cell basically presents this, um, pathogen to it, the little fragment that says which of your T-cells can recognize this, the T-cell that recognizes gets activated can undergo certain, uh, reactions that are really beyond the scope of short discussion today, and what happens to those T-cells.
And then to start to divide, make many, many copies of themselves. And then they mobilize like an army to go fight off the invader. Um, and they can literally kill, uh, cells and destroy invaders. There's other elements of the immune system that also take part in this to make antibodies and things like that. But again, we won't discuss that today that didn't do it. Excel is the key component. And the other thing that happens, uh, during this process is that certain T cells become more called memory T cells and memory T cells as the name implies stick around, uh, for our whole life, hopefully.
And they will recognize that same invader specific invader very quickly, the next time you get infected. So for example, if you're infected with one cold virus and then you become immune to, it may take several weeks for this immunity to occur. Hopefully everything goes well. But then if you get an infected with the same exact virus a year later, the T-cell will clear it and you probably wouldn't even know you were sick.
So that's how the immune system works. It's called memory, it's called the adaptive immune system because you're adapting to your environment. So we have the innate ability to recognize patterns, and that's why infants and things getting can kind of recognize pathogens, but then throughout your life, you actually become better and better at fighting things off. Now I thought I should mention, uh, COVID-19. Uh, one of the issues with COVID-19 of course is we have no idea, uh, what kind of immunity is going to be essential to, uh, prevent us from getting infected. Uh, we're trying vaccines a vaccine is really presenting the dendritic cell with something that looks like the virus that dendritic cell will then take up the vaccine, go to the lymph node, teach the T-cells that this is what to expect.
And then if we actually get infected with the real virus, like COVID-19, hopefully there'll be enough to fight it off. And if it doesn't completely eliminate it, at least, uh, hopefully we can, uh, keep the symptoms down. So people survive. Um, one of the things that, uh, we're learning about dendritic cells in the last 10 years or so is that there are many different, um, varieties or flavors if you will, of dendritic cells. And as we learn more about it, it's becoming a revolution in medicine where we actually can use dendritic cells taken out of the body and put back into people to treat cancer.
And that's been done for a number of years and we're getting better and better at that. So again, uh, dendritic cells are not the only part of the immune system that's important, but it is such a key element because it is the, the real bridge between the outside innate world and the adaptive world where we actually get lifelong immunity. And, uh, as we get older, one of the good things that happens is you get immune to more and more things on the other hand, your immune system tends to weaken and, uh, it's really important to try to stay healthy, to keep those cells, uh, in your tissues. Um, so that's it for.