This is the fourth video in a series on viruses, focusing on the coronavirus.
Once your body is infected with a virus, how does your immune system react to neutralize the threat? Furthermore, why is it that we get re-infected with the same virus year-in and year-out (think of viruses like influenza, or the coronavirus).
In this video we take a look at how the immune system operates in order to combat viruses.
For more information on the biology of viruses, visit www.evo-ed.org.
Support for this work was provided by the National Science Foundation’s Division of Undergraduate Education program under Award No. DUE2020221
many of us have had covid multiple times in recent years most of us have had multiple bouts of the cold or flu over our lifetime by and large though we’ve been able to fight off those viral infections but how to understand what our bodies do when presented with a viral infection let’s take a journey into the world of antibodies and Spike proteins and the immune system and B cells antibodies are the key to fighting off viral infections antibodies are proteins and remember proteins are the product of our DNA a stretch of DNA called the gene gets processed and ultimately produces something called a protein proteins are the molecular machines inside our cells that carry out our cellular functions antibody proteins have a unique y shape these y-shaped proteins basically have two important regions there’s a constant region and a variable region the constant region is pretty similar from one type of antibody to the next the variable region is variable different antibodies because of the unique shape of the variable region can bind to the spike protein of different viruses when this happens they essentially neutralize that virus particle an influenza antibody can bind to the spike proteins of the influenza virus but it’s ineffective against say the rotavirus because rotaviruses Spike proteins have a different shape than those of the influenza virus a rhinovirus antibody that we produce can bind to the spike proteins of the rhinovirus but it’s ineffective against say the Ebola virus because the Ebola viruses Spike proteins have a different shape than those of the rhinovirus you get the idea you can imagine given this that we would need to be able to make dozens and dozens of different types of antibodies to respond to any number of different viral infections that we might experience these y-shaped antibody proteins are made in specialized immune cells called B cells so how can our B cells make dozens and dozens and dozens of different types of antibodies each with a unique variable region and how can our B cells possibly make an antibody that’s effective against a virus that we’ve never encountered before when new B cells are made there’s a very limited and specific type of DNA scrambling that can occur which leads to a random and unique sequence for the DNA that codes for the variable region of the antibody protein this means that each new B cell has a unique and somewhat random shape when it comes to that variable region of its antibody protein since we manufacture billions and billions of B cells this means that we can make more than a billion different types of the antibody protein each with a unique variable region this makes B cells and antibodies a fantastic defense against a huge array of viruses and that’s how we can fight off viruses that we’ve never encountered before now regardless of the B cells that we’re looking at only some of the antibody proteins that are produced get secreted out of the B cell and into the bloodstream to combat viruses other antibody proteins actually remain lodged in the cell membrane of that B cell with the variable region sticking out when that variable region binds to a virus particle it causes a very slight change in the shape of that antibody protein within the B cell’s outer cell membrane that change in shape causes a Cascade of microbiological reactions to occur within the B cell that causes it to differentiate and divide but this time without the DNA scrambling that I mentioned earlier it differentiates into plasma B cells and memory B cells plasma B cells produce high levels of the relevant antibody and secrete it out of the B cell and into the bloodstream well once the viral infection has been cleared from the body most of those plasma B cells they ultimately die but those memory B cells those are stored in bone marrow and lymph nodes and in your spleen and other strategic places around the body they essentially act as an immune system database of Prior infections so that next time we’re infected by that particular virus the immune response is faster and stronger all right if we have this memory of infection then why do we get some viruses over and over again well for reasons not completely understood sometimes memory B cells are made and sometimes they aren’t in addition even if memory B cells are made sometimes they stick around long enough to confer lifelong immunity and other times they’re more short-lived also remember that the antibody response is very specific so if you’re infected with a new strain of the virus that has a mutant version of the spike protein then the antibody proteins produced by the relevant memory B cell could be a lot less effective or even entirely ineffective unfortunately viruses like the coronavirus or the influenza virus or the rhinovirus they have a very high mutation rate which means that new viral strains can have uniquely shaped Spike proteins making them immune to the antibodies that might have worked for a prior infection to learn more about virus biology and vaccines and how to kill viruses be sure to check out the other videos in our virus series thanks for tuning in I’ll see you next time [Music] thank you [Music]
