The Complement System: Definition and Function

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  • 0:34 The Complement System
  • 1:36 Opsonization and Chemotaxis
  • 3:22 Membrane Attack Complex
  • 4:21 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will cover something known as the complement system. We'll delve into the key functions of this system, including opsonization, chemotaxis, and the formation of membrane attack complexes.

Sprinkling for Defense

As any chef would know, when making a good meal, adding the exact amount of an ingredient can be critical to the success of a meal. Sometimes, the slightest sprinkle of an ingredient can make or break an expensive dish. And, that's what we'll focus in on in our lesson, the sprinkling of liquid and solid ingredients that help our body defend itself against pathogens.

The Complement System

All of the different types of sprinkles we will use in this lesson, be it solid sprinkles for cakes, or sprinkles of something like lemon juice on a fish fillet, are part of a family of ingredients called the complement system. These ingredients are molecules of the innate immune system that kill pathogens directly or help phagocytes recognize and kill a pathogen. That's just a really fancy way of saying these sprinkles, when used, help our immune system recognize or kill off an invader much more quickly than had they not been there at all.

As I said, there are many different ingredients under the complement system, and each one is a protein that is known by odd terms, such as C1, C5a, C3a, and other useless names for the purposes of this lesson. I prefer to focus in on candy sprinkles and lemon juice as the names of our ingredients instead.

Opsonization and Chemotaxis

Ok, so let's get those candy sprinkles out. There is a dark brown chocolate cake hiding in a dark corner that can really use some. When we sprinkle this brightly colored candy on top of the chocolate covered cake, I think you know what's going to happen. The sprinkles will immediately stick to the chocolate that is covering the cake, which is our bacterium in this case. This is called opsonization, which is a process by which molecules such as antibodies and complement system components make a pathogen more susceptible to phagocytosis. It's a death sentence basically. The complements, our sprinkles, stick to the cake to try and make it really yummy for a white blood cell to eat.

As soon as someone with a sweet tooth, a white blood cell, sees those brightly colored sprinkles attached to the dark brown cake, they will run towards it and gobble it all up. Once the cake is gobbled up, it will be destroyed by the enzymes inside of the white blood cells, kind of like our gastric juice in our stomach would digest and destroy a pathogen. In addition, the brightly colored sprinkles we used have a very strong fruity smell to them. Hence, they also function to attract the white blood cells to the pathogen in a process called, chemotaxis, which is a process whereby a cell finds its way to a target by way of chemical signals.

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