This lesson will describe what humoral immunity is, how it is activated, what is produced, and why. Find out as we explore antigen presenting cells, MHC, T cells, B cells, plasma cells, and antibodies.
An Educational Cruise
I think that as we learn about the basics of the immune system, we're inevitably going to get a bit tired. So I suggest a nice cruise. The catch is that this cruise isn't going to be to the Bahamas or Alaska. This cruise will be aboard a ship in your bodily fluids. Consider it an educational cruise, where we'll learn about the fundamental concepts of an important part of the immune system.
Our cruise ship, like most cruise ships, is white in color. That's because it's a ship that carries white blood cells. These are types of cells involved in protecting our body from foreign invaders, called pathogens. Not surprisingly, this white ship carries a lot of different white blood cells involved in things such as cell-mediated and humoral immunity.
In simple terms, cell-mediated immunity involves certain types of white blood cells, such as macrophages and T cells, that go out and kill the pathogens in our body. This is in slight contrast to humoral immunity, which is a system in which macromolecules, such as complements and antibodies, circulate in extracellular fluid in order to protect our body. While the macromolecules aren't cells, they still serve the same function as the cells in cell-mediated immunity: to protect our body against pathogens.
Antigen Presenting Cells
The reason we're focusing in on the antibodies in this lesson is because they are the major part of the humoral immune system. When a pathogen or part of a pathogen enters your body, it is quickly taken up by white blood cells. Some of the critical cells that do this are called antigen-presenting cells, and are cells, such as macrophages and dendritic cells, that present antigens to T cells. What that mouthful means is that a white blood cell, called an antigen-presenting cell, catches a dangerous shark, the pathogen, slices and dices it up, and then presents a recognizable piece of this shark, the antigen, to another white blood cell, called a T cell.
The antigen is presented on a sort of silver platter. This silver platter is called MHC and is more formally called the major histocompatibility complex. This is basically a molecule on the surface of the antigen-presenting cell that, like a platter, holds the antigen up to a specific type of T cell called the helper T cell.
B Cells and Plasma Cells
This helper T cell is like the busboy on the cruise line. He takes a look at the piece of shark, takes a little nibble, realizes it's a shark for sure, and runs off to tell a cook about what he found! The cook, a white blood cell called a B cell, listens to the little helper T cell, realizes that it is indeed a unique shark, and turns into another white blood cell called a plasma cell that is like the head chef on the ship. Basically, the cook got promoted to head chef because he realized there's a unique species of shark in the water that can be caught and used for dinner.
The new head chef, our plasma cell, then goes to the side of the ship and dumps out a bunch of little crabs, our antibodies, that are specific to the shark that was initially caught. These little crabs then dissolve into the surrounding sea, our bodily fluids, and begin hunting down this unique shark. Once they find this specific shark, they swarm around it and attach to the shark with their powerful pincers. Once these antibodies attach, they serve as a powerful and enticing signal for other white blood cells to swarm into the area and kill the pathogen.
The poor shark is then killed and chopped up for the dinner guests aboard the cruise line. However, that doesn't concern us much, since we need to go over the important points of humoral immunity. Humoral immunity is a system in which macromolecules, such as complements and antibodies, circulate in extracellular fluid in order to protect our body.
What basically happens is that a pathogen is engulfed by antigen-presenting cells, which are cells such as macrophages and dendritic cells that present antigens to T cells. These antigen-presenting cells chop up the pathogen and take a little recognizable piece of it, called an antigen, up to the surface of its cell. There, the antigen will be presented on a molecule on the surface of the antigen-presenting cell called MHC, or more formally the major histocompatibility complex. The little helper T cell that sees this antigen then runs off to tell a B cell to become a plasma cell. This plasma cell will then secrete antibodies specific to the pathogen that was originally engulfed by the antigen-presenting cell. The antibodies will then attach to any similar pathogen, and this attachment will act as a signal for other cells to kill the pathogen more quickly.
After viewing this video lesson, you should be able to recount the definition of humoral immune response. You may have an understanding of how the body is protected by macromolecules and antigen-presenting cells that take over a pathogen and carve it up for the MHCs, T cells, and B cells.