in this video, we're going to begin our lesson on the activation pathways of the complement system. And so first we need to recall from some of our previous lesson videos that the activation of the complement system can occur by one of three different pathways. The first pathway is going to be the alternative pathway. The second pathway is going to be the leptin pathway And the 3rd Pathway is going to be the classical pathway. Now, although these three pathways will differ in the initiation for how they activate the complement system. Notice that all three of these pathways will all converge at the formation of the Enzyme C3 converts and the Formation of C3 converters ultimately will allow for the generation of an immune response such as optimization microbe, sell license or inflammation. Now moving forward in our course, we're going to talk about each of these three activation pathways of the complement system in their own separate videos. Starting with the alternative pathway here in this video. And so the alternative pathway once again is a pathway that is capable of activating the complement system. And so the alternative pathway is activated when the complement system protein C3B, binds to the surface molecules of invading microbes. And so there's always going to be some low levels of C3 be available within the cell. And those low levels of C3B are capable of binding to the surface molecules of invading microbes. And when they bind to the surface molecules of invading microbes, they can trigger activation through the alternative pathway. So binding of the C3B will ultimately attract additional complement system proteins to bind. And eventually it will lead to the formation of the Enzyme C3 convert tastes. And once again we know that C three converters will hide relies C. Three into C. Three A. As well as C. Three B. And again C. Three B. Uh After C three convert these uh C three B will be in high level, so there will be high levels of C. Three B. After C three converted formation, whereas before C three converters formation, C three B levels are going to be low. Uh And so we know that the formation of high levels of C. Three A. And C. Three B will lead to the additional steps of the activation cascade. And uh this All this pathway can be amplified by cleaving more c. three uh to create more C three B. That combine to the microbe. And so uh this C three B. Combined two more microbe which ultimately amplifies the pathway and that can amplify the immune responses. And so, taking a look at this image down below right here again, we're showing you the complement system and the complement system can be activated by the alternative pathway and that leads to the formation of C. Three convert taste which is capable of converting C. Three and two C. Three B and C three A. C. Three A leads to inflammation Where C3B can lead to optimization or sell license of microbes. And so over here on the right hand side, we're showing you that the alternative pathway is specifically going to be activated and triggered by the molecule C. Three B. And this complement system fragment C. Three B. Is found in low levels. And so it's capable of binding to microbes and upon C. Three B binding to the surface of microbes, it will ultimately lead to the formation of C. Three converters leading ultimately to high levels of C. Three B. And C. Three A, which can trigger those immune responses. And so really the biggest thing that you should note here about the alternative pathway is that it is triggered by the complement system protein C3B. And so this year concludes our brief lesson on the alternative pathway. And as we move forward, we'll get to talk about the other pathways of complement system activation, including the lectern pathway and the classical pathway. So, I'll see you all in our next video

in this video, we're going to briefly discuss the lectern pathway, which is the second pathway of activating the complement system. And so the lectern pathway activates the complement system using pattern recognition molecules that are called manos binding lecterns. Now these manos binding lecterns are commonly abbreviated as M B L's. And so these manos binding lecterns or mbl are lecterns themselves. And recall from our previous lesson videos that elections are proteins that bind to carbohydrates. And so these manos binding lecterns or MBS, are electrons that bind to specific arrangements of manos, which is a specific type of carbohydrate. And so this man knows carbohydrate is commonly found on bacterial and fungal cell surfaces. And so these MB ELs will bind to the manners on the cell surface of bacteria and fungi. Now these bound MB ELs will interact with fragments of activated complement proteins, ultimately forming what we call the C three converting enzyme. And so we know that the C three converting enzyme is going to cleave C three into C three, B and C three A. And that will lead to these immune responses such as inflammation cell license of the microbes or optimization. And so notice over here on the left hand side was showing you our map of the complement system and it can be activated by the lectern pathway, which uses these manos binding lecterns or MB ELs and that will ultimately lead to the formation of C three converters as we just discussed. And so over here on the right hand side, we're showing you the elect in pathway, which again is going to be using these MBS. These manos binding lecterns, which again are these proteins that you can see right here in this image that bind to manos on the surface of microbes. And so the manos in this image uh is being represented by this little green structure, and again it is found on the surface of microbes. And so when the manos binding leptin binds to the manos again is capable of activating this lectern pathway, Ultimately leading to a cascade of events that leads to the formation of C. three converts. And so this here concludes our brief lesson on the lectern pathway and how it activates the complement system using MBS. And so we'll be able to get some practice applying these concepts as we move forward and then we'll get to talk about the classical pathway of complement system activation. So I'll see you all in our next video

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 for why the complement 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. And so 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. And so during the classical pathway, what happens is antibodies that are generated and 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 and a cascade of events That ultimately leads to the formation of the Enzyme C3 convert these. And so 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 classical pathway is going to utilize antibodies created an 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 C three converted. So the classical pathway which uses antibodies and complements the adaptive immune system, leads to the formation of C three converts. And we know from our previous lesson videos that the enzyme C three converts will cleave the inactive complement system protein C three into C three A and C three B. And through a cascade of events that will lead to these responses immune responses such as inflammation cell license of the microbes and or optimization. And so 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 C three converts and that can lead to eventually these immune responses. And so 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.