In this video, we're going to begin our introduction to the complement system. The complement system is a system of inactive proteins circulating in our blood and tissues, capable of initiating an immune response when these inactive complement system proteins become activated by an infection. Once again, these complement system proteins start off as inactive proteins. But upon signals of microbes during an infection, those inactive proteins can become activated proteins. The activated complement system proteins will lead to a cascade of several different reactions that ultimately generate some kind of immune response. The immune response that can be triggered by activation of the complement system includes the removal of invading microbes and inflammation, which can also help to eliminate microbes.
It is important to note that the complement system is not adaptable, which means that it does not change or adapt over time through exposures to different microbes, and thus, it is not part of adaptive immunity. Instead, the complement system is considered part of innate immunity. However, although part of innate immunity, it complements or acts in combination with antibodies and the antibody response of adaptive immunity. This is an important feature to keep in mind.
The complement system consists of these inactive proteins. The proteins can be activated by one of three different pathways that we refer to as the alternative pathway, the lectin pathway, and the classical pathway. If we take a look at our image below, notice we're showing you our map of the lesson on innate immunity. We've already talked about the first line defenses, the second line of defense and cells of immunity, and scanning systems including cell communication and pattern recognition receptors. Here in this video, we're focusing specifically on the complement system. The complement system proteins again are inactive proteins that can be activated by one of three different pathways: the alternative pathway, the lectin pathway, and the classical pathway. The classical pathway complements adaptive immunity, utilizing antibodies. We'll talk a lot more about each of these three different types of complement system activation pathways as we move forward in our course.
Another important note is that the complement system, because it consists of these inactive proteins, serves somewhat as a scanning system. It is going to be important for sensing and detecting signs of microbes. However, upon activation of the complement system proteins, those complementary system proteins can trigger innate effector actions such as phagocytosis and inflammation. The complement system, therefore, promotes phagocytosis and inflammation. We'll be able to talk more about this idea as we move forward in our course.
But for now, this here concludes our brief introduction to the complement system, and we'll be able to learn a lot more about the complement system as we move forward in our course. So I'll see you all in our next video.