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Questions and Answers
What type of proteins are defensins, cathelicidins, and histatins categorized as?
Which component of the immune system is responsible for cleaving β-(1, 4)-linkages in the bacterial cell wall?
What is the role of pattern recognition receptors (PRR) in the innate immune response?
What happens when defensins insert into the lipid bilayer of a microbial cell membrane?
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Which statement about the complement system is NOT true?
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What kind of activity does phospholipase A2 perform?
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What is the primary function of antimicrobial peptides in the innate immune response?
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What is the primary production site for complement proteins in the body?
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Which complement protein is significant in the stabilization of the alternative pathway C3 convertase?
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What term describes the process of coating a pathogen to enhance phagocytosis?
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Which of the following pathways of complement activation is directly triggered by antibodies?
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Which effector pathway is primarily associated with the action of the terminal complement proteins C5b, C6, C7, C8, and C9?
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Which of the following statements about complement products is correct?
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Study Notes
Innate Immune Response
- Physical Barrier: Epithelial cells lining the body's surfaces act as a physical barrier, with phagocytes beneath providing additional protection.
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Chemical Barriers:
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Antimicrobial Enzymes:
- Lysozyme: Breaks down bacterial cell walls by cleaving β-(1, 4)-linkages in peptidoglycan.
- Phospholipase A2: Degrades phospholipids in bacterial cell membranes.
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Antimicrobial Peptides: Short, cationic peptides with amphipathic structure (charged and hydrophobic regions) that disrupt microbial cell membranes. Examples include:
- Defensins: Disrupt cell membranes by forming pores, leading to loss of integrity.
- Cathelicidins: Activated by proteolysis, similar to defensins.
- Histatins: Amphipathic peptides activated by proteolysis.
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Complement System:
- A collection of more than 30 proteins produced by the liver, circulating in blood and body fluids.
- Many are proteases produced in inactive form (zymogens) and activated in a cascade upon detection of pathogens or pathogen-bound antibodies.
- Includes complement receptors and regulatory proteins.
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Antimicrobial Enzymes:
Complement System: Activation and Function
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Nomenclature:
- Native complement proteins: C1, C2, etc.
- Cleavage products: C3a, C3b, etc.
- Exceptions: C1q, C1r, C1s are distinct proteins that collectively form C1.
- Alternative pathway proteins: B and D.
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Activation Pathways:
- Classical Pathway: Triggered by antibodies.
- Alternative Pathway: Activated by the pathogen itself.
- Lectin Pathway: Activated by lectin-type proteins recognizing microbial surfaces.
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Effector Pathways:
- Inflammation: Mediated by C3a, C4a (weak activity), and C5a (strong activity).
- Phagocytosis (Opsonization): Facilitated by C3b and C5a.
- Membrane Attack: Involves C5b, C6, C7, C8, and C9, forming a complex that creates pores in pathogen membranes.
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Key Mechanisms:
- Lectin Pathway: Uses soluble receptors to recognize microbial surfaces and activate the complement cascade.
- Classical Pathway: Initiated by activation of the C1 complex, homologous to the lectin pathway.
- Alternative Pathway: Functions as an amplification loop for C3b formation, stabilized by properdin on pathogen surfaces.
- C3b Formation: Generates C5 convertase activity, leading to the formation of the membrane attack complex (MAC).
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Membrane Attack Complex (MAC): Terminal complement proteins polymerize, forming pores in membranes and killing certain pathogens.
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Description
Test your knowledge on the innate immune response, focusing on the physical and chemical barriers that protect the body. Explore various components such as antimicrobial enzymes, peptides, and the complement system. This quiz is designed to reinforce your understanding of the fundamental aspects of innate immunity.
