Review of the Complement System

in this video, we're going to do a review of the complement system. And so because this video is a review, what that means is that there's really no new information here in this video. And so if you're already feeling really good about the complement system then you can feel free to skip this video. But if you're looking for a good way to review a lot of the concepts that we talked about in our previous lesson videos then stick around because this might be a really helpful review for you. And so in reviewing the complement system, we're going to review the activation pathways as well as the responses or the effects of activation of the complement system. And so recall that the complement system consists of inactive proteins that are circulating in our blood and circulating through the tissues. And so these inactive complement system proteins can become activated by one of three different pathways. The alternative pathway, the lectern pathway or the classical pathway. Now the alternative pathway will activate the complement system uh and is triggered by C. Three B. A compliment system fragment binding to the surface of invading microbes. and when C3B binds to the surface of invading microbes, it helps to activate the complement system. And of course the alternative pathway is going to ultimately lead to the formation of the enzyme C. Three convert these which is actually um where all three of these pathways converge together. So the lectern pathway is going to be triggered and activate the complement system through the M. B. L. The manos binding leptin. And so the man is binding electing consists of a protein that binds to manos carbohydrates that are found on the surface of microbes. So they bind to the surface of invading microbes by binding to the manners on those microbes. So here in this image notice that the manos is represented by these little green hexagons that are on the surface of the microbe and the lectern, the man whose binding lepton or the nbl is represented by this structure that you see here. And so when the man is binding ligand binds to the manners from the surface of the microbes It will lead to a cascade of events that ultimately leads to the formation of C. three converters. And then the classical pathway is going to be triggered and activate the complement system. When antibodies from the adaptive immune system are going to bind to antigens on the surface of microbes. And ultimately these antibodies from the adaptive immune system that bind to the surface of these microbes leads to a cascade of events that once again leads to the formation of C3 converts. And this classical pathway here has an asterix next to it because the classical pathway is really why the complement system is called the complement system because through the classical pathway the complement system which is part of innate immunity is able to complement the adaptive immunity. Uh And that's because the antibodies are part of adaptive immunity and the antibodies helped to trigger the complement system which is part of innate immunity. So there's some cross talk between innate immunity and adaptive immunity right here through the classical pathway. But regardless of which pathway is used, the alternative lectern or classical pathway, they all lead to the formation of C. Three convert taste, which is an enzyme that is being represented as scissors here. Because this enzyme C three converters will cleave or fragment This inactive complement system protein called c. three. And when C three is cleaved by C three convert these, it will be cleaved into C. Three A, which is over here as well as C. Three B. Which is over here. And so there will be high levels of C. Three A. And high levels of C. Three B. After the formation of C three converts Now the c. three a. Along with other complement system proteins such as for example, C5 a. Can go on to trigger the inflammatory response to help eliminate microbes and C three B. Can go on to act as an option in to allow for optimization, which is going to improve the effectiveness of Figo psychosis, allowing faga sites like macrophages to Vegas, itas microbes much easier and much more effectively. And C3B can also interact with a series of other complement system proteins to lead to microbe cell like ISIS through the formation of membrane attack complex is that form pores in the membrane of gram negative bacteria such as these bacterial. That's being shown here. And so this year concludes our review of the complement system, and we'll be able to apply some of the concepts that are in this review as we move forward. So I'll see you all in our next video.