Questions and Answers
What are the three different pathways of complement activation?
What initiates the classical pathway of complement activation?
Antibodies bound to antigens on the microbial surface.
What is the primary function of C3b in the complement system?
To enhance the ability of macrophages and neutrophils to phagocytose material.
The alternative pathway requires specific antibodies for activation.
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Which proteins are involved in the formation of a C3 convertase in the alternative pathway?
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The classical pathway is a major effector pathway of the __________ immune response.
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Match the following components to their functions in the complement system:
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Study Notes
Functions of the Complement System
- Composed of approximately 30 proteins, both circulating and membrane-expressed, crucial for immune defense.
- Operates as an effector mechanism of both innate and antibody-mediated acquired immunity.
- Activates through three pathways: Classical, Alternative, and Mannan Binding Ligand (MBL).
- Named for its ability to "complement" antibody activity in eliminating bacteria.
Activation of the Complement
- The system recognizes and activates via three pathways, converging at the C3 component.
- Classical pathway initiated by antibodies binding to antigens on microorganisms.
- Alternative pathway triggered directly by bacterial cell surfaces.
- Lectin pathway begins when mannan-binding lectin attaches to microbial surface carbohydrates.
Classical Complement Pathway
- First delineated pathway; proteins designated C1 to C9 based on discovery order, not functionality sequence.
- Antigen-antibody complexes are the primary activators, linking this pathway to the humoral adaptive immune response.
- Initial activation involves C1 binding to antibodies, leading to C1 esterase formation.
- C1 esterase acts on C4, producing C4b that binds with it, forming a complex that interacts with C2, yielding C2a and C2b.
- C4b2b complex functions as a C3 convertase, cleaving C3 into C3a and C3b.
- C3a and C5a induce inflammation and recruit neutrophils, while C4b2b3b activates the membrane attack complex (MAC).
- MAC creates pores in target membranes, facilitating cell lysis.
Important Functions of the Complement System
- Produces opsonins like C3b to enhance phagocytosis by macrophages and neutrophils.
- Induces chemotaxis through C3a and C5a, attracting neutrophils to pathogens.
- Generates anaphylatoxins (C3a, C5a), causing degranulation of basophils and mast cells, invoking local/systemic inflammation.
- Facilitates lysis of targets coated with antibodies via MAC through C8 and C9.
The Alternative Pathway
- Activated by diverse microbial products including lipopolysaccharides from gram-negative bacteria, without specific antibodies.
- Comprises unique elements like factors B and D, and properdin, along with common components C3 through C9.
- Begins when C3b, formed from spontaneous hydrolysis, binds to microbial substances.
- Leads to the formation of the C3 convertase C3BbBP to cleave C3 into C3a and C3b, continuing complement activation.
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Description
Explore the essential functions of the Complement System through this set of flashcards. Each card presents vital information about the proteins involved and their roles in immune defense mechanisms. Perfect for students studying immunology or related health sciences.
