In this video, we're going to briefly introduce the classical pathway which is the third activation pathway of the complement system. And so this classical pathway is capable of activating the complement system by using antibodies that are created in adaptive immunity. And so really, this classical pathway is the whole reason why the system is called the complement system. And this is because although the complement system is considered part of innate immunity, it does complement the adaptive immune responses. And that's because antibodies are part of adaptive immune responses, and this classical pathway will use antibodies to activate the complement system.
First, we need to recall a few terms such as the term antigens, which refers to any toxin or foreign substance that induces an antibody immune response, and the term antibody, which refers to Y-shaped proteins that can recognize and bind to an antigen. During the classical pathway, what happens is antibodies that are generated in adaptive immunity will bind to antigens on the surface of microbes. And those antibodies that are bound to the surface of microbes can then interact with other activated complement proteins in a cascade of events that ultimately leads to the formation of the enzyme C3 convertase.
If we take a look at our image down below over here on the left hand side, notice we're showing you our map of the lesson on the complement system. And again, we're focusing on the activation pathways, specifically the classical pathway here. And, the pathway is going to utilize antibodies created in adaptive immunity. And these Y-shaped proteins, these antibodies, they will bind to antigens on the surface of microbes, and those bound antibodies will interact to form C3 convertase. So the classical pathway, which uses antibodies and complements the adaptive immune system, leads to the formation of C3 convertase, and we know from our previous lesson videos that the enzyme C3 convertase will cleave the inactive complement system protein C3 into C3a and C3b, and through a cascade of events that will lead to these responses, immune responses such as inflammation, cell lysis of the microbes, and or opsonization.
Over here on the right, we're focusing specifically on this classical pathway. And again, the classical pathway is going to utilize antibodies, these Y-shaped proteins, that are formed in adaptive immunity. And these antibodies will bind to antigens on the surface of the microbes. And so notice that these microbes that you see down below, they have these antigens on their surface. And the antibodies, these Y-shaped proteins right here, that are produced during adaptive immunity, they will bind to these antigens. And upon binding to the antigens, these antibodies will interact with a series of other complement system proteins that ultimately leads to the formation of C3 convertase, and that can lead to eventually these immune responses.
This here concludes our brief lesson on the classical pathway and how it goes about activating the complement system. And so I'll see you all in our next video.