Questions and Answers
How many proteins is the Complement System composed of?
30+ proteins
What are Proteases active only after cleavage usually by another specific protease?
Complement Proteins
What is the inactive form of a complement protein called?
Proenzymes or Zymogens
Where is the complement system produced?
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When is the complement system activated?
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Where is the Complement system activated?
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Which two antibodies are capable of initiating complement activation?
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What are the effector functions of the Complement System?
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What are the three functions of the Complement System?
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How do the Complement System proteins get activated?
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What is the innate immune system composed of?
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How many Complement pathways are there?
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What do the complement pathways have in common?
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What happens when the complement protein coats the outer surface of a pathogen?
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What is caused by a group of complement proteins forming a hole in a pathogen?
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What is the first complement pathway to be discovered?
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How is the Classical pathway triggered?
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What is the first step of the Classical pathway?
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What happens in the 2nd step of the Classical pathway?
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What involves C4 cleavage and which enzymes are responsible?
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What kind of bond is formed when C4b covalently binds to an antigen?
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What happens when C2 comes in contact with the C1 complement complex?
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Which proenzyme binds to C4b?
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What activates and cleaves C2 proenzyme attached to C4b?
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What happens to C2a and C2b after cleavage?
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What is C1 Complement Complex composed of?
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What does C1q bind to?
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What does C1 Complement Complex binding to Antibody:Antigen complex activate?
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Which component cleaves and activates in the Classical Pathway?
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What is the product of cleaving C4?
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What does C1s cleave C2 into?
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What does C4bC2a form?
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What does C3 Convertase do?
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What does C3a trigger?
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What happens to C3b?
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What is C5 Convertase?
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What does C4b3b2a represent?
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What does C5 Convertase do?
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Study Notes
Complement System Overview
- Composed of over 30 proteins that circulate in an inactive form to prevent self-attack.
- Activation occurs when proteins encounter pathogens or antibody-bound antigens on cell surfaces.
Proteins and Activation
- Inactive forms of complement proteins are referred to as proenzymes or zymogens.
- Active proteases induce a cascade of interactions to trigger further complement activation.
- Notable antibodies, IgM and IgG, initiate complement activation upon binding to antigens.
Key Processes and Functions
- Major effector functions include opsonization, formation of the Membrane Attack Complex (MAC), and triggering inflammation.
- Opsonization marks pathogens for easier phagocytosis by immune cells.
- MAC creates pores in pathogen membranes, leading to cell lysis.
Complement Pathways
- There are three complement pathways: classical, alternative, and lectin, all designed to activate C3 to C3 Convertase.
- The classical pathway is the first discovered and gets triggered by antigen-antibody complex formation.
Classical Pathway Steps
- Antibodies bind to antigens on pathogens, leading to the binding of the C1 complex.
- C1 complex cleaves C4 into C4a and C4b, where C4b covalently bonds to the pathogen surface.
- C2, upon contact with C1 complex, is cleaved into C2a and C2b; C2a binds to C4b to form C3 Convertase (C4b2a).
Cleavage and Product Formation
- C3 Convertase cleaves C3 into C3a and C3b, perpetuating the complement response.
- C3a promotes inflammation, while C3b can opsonize pathogens or bind to antibody complexes.
C5 Convertase
- C5 Convertase is formed when C3b binds to C4b2a, and it cleaves C5 into C5a and C5b.
- Cleavage products C4a, C4b, C2a, and C2b play roles in further complement activation and regulation.
Components of C1 Complex
- C1 complement complex includes C1q (pathogen sensor), C1r, and C1s.
- C1q binds to antibody-antigen complexes, activating downstream proteases C1r and C1s for further complement activation.
Important Binding Characteristics
- C4b forms covalent bonds with pathogen surfaces, crucial for opsonization and complement activity.
- The sequential nature of complement activation ensures a rapid immune response against pathogens.
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Description
Test your knowledge on the classical and lectin pathways of the complement system with these flashcards. Gain a deeper understanding of the proteins involved, their activation, and the overall function of this important immune system component.