 Hey everybody, Dr. O here. In this video we're going to talk about antigenic variation and how organisms use it to hide from, evade the immune system. So first just a real quick primer on the immune system. So antibodies are a huge part of your immune system. They're produced by B cells and they're looking for antigens, which are cell surface markers. So I always think of the immune system especially the memory portion of your immune system as looking at wanted posters. So a wanted poster is here's the cell surface markers, here's the features we know about this bank robber, whatever, right from the old cowboy movies. So antigens are cell surface markers, antibodies are looking for those cell surface markers. So antigenic variation is how organisms change their antigens, change their cell surface markers so they no longer look like that, right? So if I robbed a bank, I'd shave my goatee, I'd get rid of my gray hair, I'd change my clothes, et cetera, et cetera. So this is antigenic variation. So we're primarily going to focus here on how this works with the influenza virus, the flu virus. But there's a couple of real quick examples, bacteria can do this as well, Beryllia burgdorferi which causes the causative agent of Lyme disease can do this. So basically every time someone has a fever with Lyme disease, you're seeing a change in the cell surface markers and that's why it can become a chronic disease. You also have Niseria gonorrhea, the causative agent of gonorrhea. It changes what it's actual, it's pili on it, one of the cell surface structures looks like for the same reason. So there are bacteria that can do this, but let's primarily focus on the influenza virus. So let's talk about the two examples and then we'll talk about where flu pandemics come from and then we'll talk about the vaccine and why it only works so well and it has to be taken annually. So first we have antigenic drip. This is just going to be mutations, right? Viruses mutate more quickly than bacteria. So viruses mutate quite often, which means they're going to have these point mutations or base substitutions where every once in a while a piece of genetic material is going to change and that's going to change what the surface looks like. So you're seeing here that these surface antigens, the hemagglutinins and neuramidases, they can actually change over time because of mutation. So that's an example of an antigenic drift, this slow, steady changing of what the outside of the flu virus looks like. Antigenic shifts are going to occur when one person is infected with two different influenza viruses. So here you see virus A, virus B, they actually reassort and swap their genes and out spits virus C, which looks a lot different. So antigenic shift is where most, if not all, of the influenza pandemics, like the flu pandemic of 1918 that killed 30 to 50 million human beings, 600,000 Americans, or the other flu pandemics came from. So antigenic shifts are going to be huge changes in what the outside, the surface of the flu virus looks like. So these slow and steady changes, the antigenic drift and these rapid changes, antigenic shift, this is constantly changing what the outside of the flu virus looks like. This is why the flu vaccine has to be taken annually. So because you have to basically, they have to try to look and one of the biggest problems of the flu vaccine is how long it takes to produce. So they have to look and try to guess what are the three or four or five strains of the flu that were most likely to see next year in the next flu season and they produce vaccines against those. But since it changes every year, you don't have a flu vaccine that can be taken once and forgotten about or you need a booster every 10 years, whatever. This is why the flu vaccine is taken annually. This is also why the flu vaccine is not super effective. So I mean, it is helpful, but you see numbers like between 3040 or 70% effective. So lower than many vaccines because the flu is constantly changing. So if a vaccine protects you against the flu viruses you see here on the screen, but they slowly change, they change their outfit, they change their disguise, your immune system is not going to be able to recognize these new strains. So that is antigenic variation or one of the ways that organisms evade your immune system by constantly changing what they look for. Now in the future, could we see a flu vaccine that you can take once? I guess what you would say, you'd have to create a vaccine that was looking for something on the flu virus that never changed. So no matter what parts of the disguise the bank robber is changing, there has to be something there that didn't change and that would be what your immune system is looking for. So it is possible, but we're not there yet. All right, that is antigenic variation. I hope this helped. Have a wonderful day. Be blessed.