Podcast
Questions and Answers
What is the primary difference between the classical pathway and the lectin activation pathway?
What is the primary difference between the classical pathway and the lectin activation pathway?
What is the role of the C1 complex in the classical pathway?
What is the role of the C1 complex in the classical pathway?
What is the outcome of the convergence of the three distinct pathways of complement activation?
What is the outcome of the convergence of the three distinct pathways of complement activation?
What is the function of the lectin activation pathway?
What is the function of the lectin activation pathway?
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What is the difference between the classical pathway and the alternative pathway?
What is the difference between the classical pathway and the alternative pathway?
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What is the purpose of opsonization in the immune response?
What is the purpose of opsonization in the immune response?
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Which of the following is NOT a function of the complement system?
Which of the following is NOT a function of the complement system?
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What is the role of mannose-binding lectin in the lectin activation pathway?
What is the role of mannose-binding lectin in the lectin activation pathway?
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What is the primary function of the C3 protein in the complement system?
What is the primary function of the C3 protein in the complement system?
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What is the outcome of the lectin activation pathway?
What is the outcome of the lectin activation pathway?
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Study Notes
The Complement System
- The complement system is part of the innate immune response, providing immediate defense against infection.
- It consists of over 30 proteins that work together to eliminate pathogens from the body.
Alternative Pathway
- The alternative pathway is initiated by the spontaneous activation of C3, producing C3a and C3b.
- C3b attaches to the surface of invading microbes, recruiting other complement proteins to form a cascade.
- This pathway is triggered by the presence of invading microbes and results in the activation of C3.
Activation of Complement Proteins
- The three complement activation pathways have different triggers but all result in the activation of C3, producing C3a and C3b.
- C3b binds to the surface of the target cell, leading to the formation of the membrane attack complex (MAC).
- The MAC punches through the cell membrane of the invading pathogen, causing it to burst.
Protective Outcomes
- The complement system provides the following protective outcomes:
- Opsonization: coating of a pathogen by an opsonin, making it easier for phagocytic cells to recognize and engulf.
- Inflammation: attracting white blood cells to the site of infection.
- Chemotaxis: guiding white blood cells to the site of infection.
- Cytolysis: lysis of the infected cell.
Opsonization
- Opsonins from the complement cascade include C1q, C3b, and C4b.
- Additional opsonins include mannose-binding proteins and antibodies.
Anaphylatoxins
- C3a and C5a are anaphylatoxins with potent proinflammatory functions.
- They activate mast cells, causing degranulation and the release of inflammatory chemical signals.
- C5a is a potent chemoattractant for neutrophils and other white blood cells.
Membrane Attack Complex (MAC)
- The complement proteins C6, C7, C8, and C9 assemble into a MAC.
- The MAC forms pores in the membranes of gram-negative bacteria, leading to cell lysis and death.
- The MAC is only effective against gram-negative bacteria and not gram-positive bacteria.
Cytokines
- Cytokines are soluble proteins that act as communication signals between cells.
Classical Pathway
- The classical pathway is initiated by the binding of a specific antibody to a pathogen, forming an antibody-antigen complex.
- The C1 complex is activated, leading to the recruitment and activation of the remaining classical pathway complement proteins.
Lectin Activation Pathway
- The lectin activation pathway is triggered by the binding of mannose-binding lectin to carbohydrates on the microbial surface.
- It is similar to the classical pathway but does not require the presence of antibodies.
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Description
This quiz covers the alternative pathway of the complement system, including the role of lectins and C3 protein in response to inflammation and infection.
