Introduction to the Complement System - Video Tutorials & Practice Problems

Complement System

In this video, we're going to begin our introduction to the complement system. And so the complement system is really just a system of inactive proteins that are found circulating in our blood and in our tissues. And they are capable of initiating an immune response when these inactive complement system proteins become activated by an infection. And so 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. And the activated complement system proteins will lead to a cascade of several different reactions that ultimately generate some kind of immune response. And the immune response that can be triggered by activation of the complement system includes removal of invading microbes and inflammation, which can also help to eliminate microbes. Now, it is important to note that the complement system is not adaptable, which means that the complement system does not change or adapt over time through exposures to different microbes, which means that the complement system is not part of adaptive immunity. Uh And so the complement system instead is considered part of innate immunity. And uh it is important to note that however, uh although the complement system is part of innate immunity, it does complement or act in combination with antibodies uh and with the antibody response of adaptive immunity. And so this compliment system, although it is part of innate immunity, it does complement or act in combination with adaptive immunity. And so that is an important feature to keep in mind. Now, the complement system once again consists of these inactive proteins. And uh the complement system 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. And so if we take a look at our image down below, notice we're showing you our map of the lesson on innate immunity. And we've already talked about the first line defenses and we know that we've talked about the second line of defense and cells of immunity. And uh we've talked about scanning systems including cell communication and pattern recognition receptors. So here in this video, we're focusing specifically on the complement system and 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. Now it turns out that it's this classical pathway over here that is going to complement adaptive immunity. And so uh notice that it does utilize antibodies and we'll get to talk a lot more about each of these three different types of complement system activation pathways as we move forward in our course. Now, another thing that's important to note is that the complement system uh because it consists of these inactive proteins, uh it does serve somewhat as a scanning system. So it is going to be important for sensing and detecting signs of microbes. However, upon activation of the complement system proteins, those complement system proteins can trigger innate effector action such as for example, PAG oy tosis and inflammation. And so the complement system we're saying here uh can promote or promotes phagocytosis and inflammation. And we'll be able to talk more about this idea as we move forward in our course. But for now, this year 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.

What does the word “complement” mean in the name complement system?

• A. This is a system of proteins that complements or enhances the abilities of the immune system to kill microbes.
• B. This is a system of proteins that replaces the innate immune system when the infection is too extreme.
• C. This is a system of proteins that competes with the adaptive immune system to kill pathogens.

Which of the following are results of activation of the complement system? 

1. Removal or destruction of microbes. 2.  Inflammation. 3.  Production of antibodies.

• A. 2 only.
• B. 1 and 2.
• C. 3 only.
• D. 1, 2, and 3.

Proteins of the Complement System

In this video, we're going to briefly talk about the proteins of the complement system. And so the complement system proteins are all designated with a letter C and they are numbered C one through C nine in terms of the order of their discovery where C one was discovered first and C nine was discovered last. Now, these complement system proteins, once again, they remain inactive and so they circulate through our blood and in our tissues as their inactive forms until these complement system proteins are fragmented. And once these complement system proteins are fragmented, they become activated and the activated fragments are indicated by lowercase letters such as for example, the lowercase letter A and the lowercase letter B. Now the complement system protein C three is a very important and a very critical complement system protein. And once again, these complement system proteins are going to exist in their inactive forms. And so C three is a critical inactive complement system protein. And the C three complement system protein can become activated by the activity of an enzyme called C three converse. And so C three converse is an enzyme that will activate C three by hydrolyzing or fragmenting C three into the C three A and C three B fragments. And so the C three A and C three B fragments, which are active can interact with other complement system components, ultimately causing some kind of immune response. And uh recall that the immune responses of complement system activation include optimization, cell lysis and inflammation, all which we'll get to talk more about as we move forward in our course. And so if we take a look at our image down below, notice what we're showing you here at the top is the enzyme C three converse which is being represented here as this pair of scissors because its function is to enzymatic cleave or fragment C three. And so notice here, we have the complement system protein C three right in the middle and C three converse is an enzyme that will cleave or fragment C three into the activated activated fragments. C three A and C three B and so C three A and C three B through a cascade of reactions can ultimately lead to these immune responses. Such as for example, C three A can lead to inflammation and inflammation is an innate immune response that can help to eliminate microbes. And we'll get to talk a lot more details about inflammation later in our course. Uh And C three B can lead to a process known as opsonization, which we'll get to talk more about moving forward in our course. As well, but it helps to improve phagocytosis and it can also lead to cell lysis. And so here we're showing you a microbe that is being laced. And so, ultimately, what we're saying here is that these proteins of the complement system need to become activated and upon activation, they can lead to immune responses such as inflammation and oxidization or cell lysis. And so this year concludes our brief lesson on the proteins of the complement system. And we'll be able to learn more about the complement system as we continue to move forward. So I'll see you all in our next video.

If the complement proteins are always present in the body, then why are the results of the complement system not always occurring?

• A. The complement system proteins need to be activated by the invasion of a microbe.
• B. The complement system proteins are held in the lymph nodes until an infection occurs.
• C. The complement system proteins are inactive until cleaved by another complement protein.
• D. The complement system proteins are not always present and only translated when an infection occurs.
• E. A and B.
• F. A and C.
• G. D only.

Map of the Lesson on the Complement System

In this video, we're going to introduce our map of the lesson on the complement system, which is down below right here. And so we can go ahead and label the title of this map, the complement system. Now, uh activation of the complement system can actually be initiated by one of three different pathways which are the alternative pathway, the lectin pathway or the classical pathway. Now, each of these three different pathways does differ in the initiation of how they go about activating the complement system. However, although they differ in the initiation, all three pathways end up resulting in the formation of the enzyme C three converse. And recall from our last listen video that C three converse is an enzyme that is capable of activating the complement protein C three by fragmenting it into C three A and C three B. And of course, we know that C three converse can end up resulting in three possible effects or three possible immune responses, which are ization cell lysis of the invading microbe or the inflammatory response leading to inflammation. And so as we move forward in our course, we're going to talk about these three different pathways that activate the complement system. And we'll also get to talk about these three effects that uh can result from activation of the complement system. And so if we take a look at our image down below, notice that the complement system again consists of these inactive proteins that circulate in the blood and in our tissues. And these inactive complement system proteins can become activated uh through one of three different pathways. The alternative pathway, the lectin pathway or the classical pathway. Now notice that the classical pathway here has this little asterisk because uh the classical pathway is the one that complements the adaptive immunity. And so uh the classical pathway is going to utilize antibodies which helps it complement the adaptive immunity. Now, uh notice that all three of these pathways, alternative lectin and classical pathways, they all differ in how they initiate activation of the complement system. However, notice that all three pathways converge eventually at the formation of this enzyme C three converse. And we know from our last lesson video once again that C three converse will enzymatic cleave C 32 C three A and C three B, which can ultimately lead to these three immune responses, oxidization or improved phagocytosis microbe clysis or the inflammatory response. And so those are the effects of activation of the complement system. Now, this year again concludes our map of the lesson on the compliment system. But as we move forward, we're going to talk more details about all of these different things that you see here. So I'll see you all in our next video.

How do the three pathways of the complement system differ?

• A. The pathways differ in the resulting immune response they trigger.
• B. The pathways differ in the complement proteins that they activate.
• C. The pathways differ in what triggers the initiation of the pathway.

The possible effects of the lectin pathway of the complement system are?

• A. C3 convertase formation.
• B. Opsonization of infecting microbes.
• C. Cell lysis of infecting microbes.
• D. Triggering the inflammatory response.
• E. All of the above.