Podcast
Questions and Answers
What is the primary site of complement synthesis in the body?
What is the primary site of complement synthesis in the body?
Which of the following statements about the complement system is true?
Which of the following statements about the complement system is true?
Which pathway is NOT a method of complement activation?
Which pathway is NOT a method of complement activation?
The complement system is primarily located in which of the following?
The complement system is primarily located in which of the following?
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Which of the following is a component of the adaptive immune response that activates complement?
Which of the following is a component of the adaptive immune response that activates complement?
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Which pathway of complement activation is dependent on antibodies?
Which pathway of complement activation is dependent on antibodies?
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Which of the following pathways does not rely on antibodies for its initiation?
Which of the following pathways does not rely on antibodies for its initiation?
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What is generated as a result of C3 activation in complement pathways?
What is generated as a result of C3 activation in complement pathways?
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Which pathway is directly involved in lytic attacks?
Which pathway is directly involved in lytic attacks?
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Which statement is true regarding the pathways of complement activation?
Which statement is true regarding the pathways of complement activation?
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Which of the following is a benefit provided by opsonization?
Which of the following is a benefit provided by opsonization?
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What is one of the detrimental effects of an immune response?
What is one of the detrimental effects of an immune response?
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Which of the following statements is true regarding phagocyte function?
Which of the following statements is true regarding phagocyte function?
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What is the role of lysis in the immune system?
What is the role of lysis in the immune system?
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Which option does not represent a benefit of the immune response?
Which option does not represent a benefit of the immune response?
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What initiates the classical pathway of the immune response?
What initiates the classical pathway of the immune response?
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Which components make up the C1 complex in the classical pathway?
Which components make up the C1 complex in the classical pathway?
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What is the primary product of the classical pathway after the activation of C1?
What is the primary product of the classical pathway after the activation of C1?
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Which antibodies are mentioned as part of the activation of the classical pathway?
Which antibodies are mentioned as part of the activation of the classical pathway?
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What happens when the Ag-Ab complex binds to C1?
What happens when the Ag-Ab complex binds to C1?
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What is the primary function of the complement protein C3?
What is the primary function of the complement protein C3?
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How many inactive complement protein molecules are present in the bloodstream?
How many inactive complement protein molecules are present in the bloodstream?
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Which pathways are involved in the activation of the complement system?
Which pathways are involved in the activation of the complement system?
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Where does the activation of the complement system primarily occur?
Where does the activation of the complement system primarily occur?
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What characteristic of complement protein C3 contributes to its role in the complement system?
What characteristic of complement protein C3 contributes to its role in the complement system?
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What type of immunity is associated with the classical pathway?
What type of immunity is associated with the classical pathway?
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Which component is NOT involved in the alternate pathway of complement activation?
Which component is NOT involved in the alternate pathway of complement activation?
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What initiates the alternate pathway in the complement system?
What initiates the alternate pathway in the complement system?
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Which complement protein is excluded in the alternate pathway?
Which complement protein is excluded in the alternate pathway?
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Which statement accurately compares the classical and alternate pathways?
Which statement accurately compares the classical and alternate pathways?
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What role does C1q play in the classical pathway?
What role does C1q play in the classical pathway?
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Which complement components are involved in the activation stage of the classical pathway?
Which complement components are involved in the activation stage of the classical pathway?
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What occurs during the membrane attack stage (MAC) of the classical pathway?
What occurs during the membrane attack stage (MAC) of the classical pathway?
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In which sequence does the activation stage of the classical pathway occur?
In which sequence does the activation stage of the classical pathway occur?
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Which of the following is NOT a component of the membrane attack complex?
Which of the following is NOT a component of the membrane attack complex?
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What activates the alternate pathway of the immune response?
What activates the alternate pathway of the immune response?
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Which component does NOT bypass the alternate pathway activation?
Which component does NOT bypass the alternate pathway activation?
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What is the role of C3b in the context of the alternate pathway?
What is the role of C3b in the context of the alternate pathway?
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What occurs in healthy conditions concerning C3 cleavage?
What occurs in healthy conditions concerning C3 cleavage?
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Which of the following describes the nature of immunity provided by the alternate pathway?
Which of the following describes the nature of immunity provided by the alternate pathway?
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What is the composition of the membrane attack complex (MAC)?
What is the composition of the membrane attack complex (MAC)?
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What is the primary function of the membrane attack complex (MAC) in the immune response?
What is the primary function of the membrane attack complex (MAC) in the immune response?
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In the diagrams of the membrane attack complex (MAC), what does the purple protein tube represent?
In the diagrams of the membrane attack complex (MAC), what does the purple protein tube represent?
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How does the MAC initiate damage to the target cell?
How does the MAC initiate damage to the target cell?
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What role does the fluid in the right diagram, representing the blue fluid, play in relation to the MAC?
What role does the fluid in the right diagram, representing the blue fluid, play in relation to the MAC?
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What initiates the lectin pathway of complement activation?
What initiates the lectin pathway of complement activation?
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How does mannose-binding lectin (MBL) relate to the classical pathway?
How does mannose-binding lectin (MBL) relate to the classical pathway?
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What is a characteristic of the lectin pathway in terms of antibody dependence?
What is a characteristic of the lectin pathway in terms of antibody dependence?
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What is the outcome after mannose-binding lectin (MBL) binds to mannose on microbes?
What is the outcome after mannose-binding lectin (MBL) binds to mannose on microbes?
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Which statement is true regarding the sequence of the lectin pathway?
Which statement is true regarding the sequence of the lectin pathway?
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Study Notes
Complement System Overview
- Complement consists of proteins essential for host defense.
- Found in serum and all tissue fluids except urine and cerebrospinal fluid (CSF).
- Synthesized primarily in the liver.
- Supports immune and inflammatory responses, involving both innate and adaptive immune pathways.
Activation Pathways
- Complement activation is triggered by:
- Antigen-antibody complexes (adaptive immune response).
- Endotoxins or polysaccharide capsules (innate immune response).
- Three pathways for activation:
- Classical pathway: antibody-dependent.
- Alternative pathway: antibody-independent.
- Lectin pathway: antibody-independent.
Key Components and Functions
- Circulates as 30 inactive protein molecules in the bloodstream.
- C3 is the most abundant complement protein, central to all pathways, but is unstable and rapidly breaks down.
Host Benefits of Complement Activation
- Enhances phagocytosis via opsonization.
- Attracts and activates phagocytes.
- Causes lysis of bacteria and infected cells.
- Regulates antibody responses.
- Clears immune complexes.
Host Detriments of Complement Activation
- May lead to inflammation.
- Potential for anaphylaxis.
Detailed Pathway Functions
Classical Pathway
- Activated through antigen-antibody complexes.
- C1 (made of C1q, C1s, and C1r) binds to the Fc region of IgM or IgG.
- Sequence includes:
- Recognition Stage: C1q identifies and binds to antibodies.
- Activation Stage: Involves C4, C2, C3, C5, C6, C7, C8, and C9 in order.
- Membrane Attack Stage (MAC): C5b, C6, C7, C8, and C9 lead to cell lysis.
Alternative Pathway
- Activated without antibodies, often by lipopolysaccharides (LPS) from Gram-negative bacteria.
- Supports non-specific resistance.
- C3 cleaves into C3a and C3b; C3b binds to microbial surfaces to create stable C3 convertases (C3bBb).
Lectin Pathway
- Activated by mannose-binding lectin (MBL) or mannose-binding protein (MBP), targeting mannose on microbial surfaces.
- Activation completes the same sequence as the classical pathway.
Terminal Steps (Lytic Pathway)
- All three pathways converge at C5b, C6, C7, C8, and C9 to form the membrane attack complex (MAC).
- MAC causes lysis of target cells by forming pores in their membranes.
Comparison of Classical and Alternative Pathways
-
Classical Pathway:
- Linked to acquired immunity.
- Initiated by antigen-antibody complexes.
- Involves all complement proteins.
-
Alternative Pathway:
- Part of innate immunity.
- Initiated by microbial surface structures.
- Does not involve C1, C4, or C2, but utilizes Properdin (FP).
Regulation of the Complement System
- Regulation is crucial to avoid excessive activation and potential tissue damage.
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Description
This quiz covers essential aspects of the complement system, including its definition, synthesis, site, and function in immune responses. Explore how complement proteins contribute to both innate and adaptive immunity and their role in inflammation. Test your knowledge on these critical components of host defense.