Complement System

by Peter Delves, PhD

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    You’ve heard me talk about complement. You’ve heard me mention complement. You may be wondering, what is this? What is complement? Well, it’s not a single molecule. It’s a series of molecules, it’s a complement system. And this system of molecules and regulators of those molecules and receptors for those molecules are incredibly important in host defense against infection. Complement can be activated by three different pathways. Firstly, the classical pathway. It’s called the classical pathway because this was the pathway of complement activation that was initially discovered. And at that time, it was thought there was just one pathway. Things were simple; the complement activation pathway. But subsequently, the other two pathways were discovered. So the first pathway was renamed the classical pathway. The one everybody knew about. And this is activated when an antibody binds to an antigen. In other words, antibody-antigen complexes are formed. There are other ways in which the classical pathway of complement can be activated. For example, C-reactive protein, an acute phase protein that was mentioned in the… a few slides ago. This C-reactive protein (CRP), can also activate the classical pathway of complement. So, antibody binding to antigen will activate the first component in the complement system which is called complement component C1q. This then helps to recruit two other components of C1 called C1r and C1s. These C1 components activate complement component C4, which then goes on and activates complement component C2. You’ll notice that the order of these doesn’t seem to go with the normal order. Normally we have one, two, three, four, don’t we? But these complement components were actually ordered in the… or named rather in the order they were first discovered. So scientists discovered complement component C2 before they discovered C4. But when the details of the pathways...

    About the Lecture

    The lecture Complement System by Peter Delves, PhD is from the course Innate Immune System. It contains the following chapters:

    • The Complement System
    • Main Functional Components of the Complement System

    Included Quiz Questions

    1. MASP-1
    2. Factor B
    3. Factor D
    4. C1q
    5. C3bBb3b
    1. Alternative- microbial sugars
    2. Classical- antibody antigen complexes
    3. Classical- CRP
    4. Lectin- microbial sugars
    5. Alternative- microbial structures
    1. C3b
    2. C3a
    3. C5a
    4. C4
    5. C5b6789
    1. C3a, C5a
    2. C3a, C3b
    3. C3b, C5a
    4. C5a, C5b6789
    5. C3a, C5b6789
    1. They are responsible for the cleavage of C3 and C5, creating C3a/C3b and C5a/C5b- which are responsible for activating the bulk of the complement immune response.
    2. They are active early in the Classical Pathway of complement activation.
    3. They help activate lymphocytes that respond to antigens that activate complement
    4. They mediate complement by halting converting active complement factors back to their inactive form
    5. They stimulate degranulation of mast cells and basophils

    Author of lecture Complement System

     Peter Delves, PhD

    Peter Delves, PhD

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    Finally got the complement system
    By Bjarni J. on 22. December 2016 for Complement System

    Had been watching so much on this and never understood it.