B13: mucosal immunity Flashcards
: What are the two main functions of mucosal surfaces?
Facilitate exchanges (e.g., food, gas, reproduction) and form a barrier against biological, chemical, and physical insults.
How large is the surface area of mucosal tissues compared to skin?
Mucosal surfaces: ~120 m²; Skin: ~2 m².
What is DALY, and why is it important in mucosal infections?
Disability-Adjusted Life Years (DALY) measures disease burden by combining morbidity and mortality.
🛡️ Name the three levels of mucosal defence.
Immediate innate immunity, induced innate immunity, adaptive immunity.
Give examples of mechanical, chemical, and microbial innate defences.
Mechanical: Tight junctions, mucus.
Chemical: Lysozyme, lactoferrin, antimicrobial peptides.
Microbial: Commensal microbiota competes with pathogens, produces antimicrobials (e.g., H₂O₂), regulates immune responses.
🛡️ How does adaptive immunity differ from innate immunity?
🛡️Adaptive immunity is highly specific and requires activation, while innate immunity is immediate and non-specific.
🏗️What are the functions of epithelial cells in mucosal immunity?
🏗️Barrier function, antimicrobial secretion (e.g., SIgA), immune sensing (via TLR/NOD receptors), cytokine production (e.g., NFkB pathway), xenophagy.
🏗️Describe the two sides of epithelial cell polarity.
🏗️Apical side: Faces external environment (e.g., gut lumen, airways).
Basolateral side: Connects to other cells and extracellular matrix.
🏗️ What is transcytosis?
🏗️ Vesicle-mediated transport across epithelial cells (e.g., for SIgA antibodies or pathogens).
🧱What are the four key layers of the gut mucosal barrier?
🧱Mucosal microbiota, mucus layers (inner/outer), epithelial cells, mucosal leukocytes/stromal cells (e.g., dendritic cells, B/T cells).
🦠What percentage of immune cells work at mucosal sites?
🦠Around 80%.
🦠What are the two arms of mucosal immunity, and what happens at each?
🦠Innate arm: Epithelial cells and immune cells (e.g., macrophages) within the lamina propria.
Adaptive arm:
Inductive sites: Antigen sampling, B/T cell activation (e.g., MALT).
Effector sites: Activated lymphocytes perform functions (e.g., within lamina propria, glands, surface epithelia).
🦠What makes the mucosal adaptive immune system unique?
🦠Specialised antigen sampling (M cells), unique homing (e.g., CCR9, CCR10 receptors), dominant SIgA production, suppressive mechanisms to maintain tolerance.
🔍How does the mucosa sample antigens despite physical barriers?
🔍M cells: Specialised epithelial cells transport antigens.
Dendritic cells/macrophages: Extend into lumen for sampling.
Alveolar macrophages: Sample antigens in the lungs.
🔍How does SIgA function in mucosal immunity?
🔍Binds pathogens/toxins on the surface, neutralises internal antigens, exports toxins, delivers antigens to dendritic cells.
🔍How do antibody responses differ between systemic and mucosal sites?
🔍Systemic B cells: ~52% IgG.
Mucosal B cells: ~80% IgA (dimeric with J-chain + secretory component).
Name examples of effective, variable, and absent mucosal vaccines.
Effective: Poliovirus, HPV, coronaviruses.
Variable efficacy: Rotavirus, influenza.
No vaccines yet: HIV.
🛡️ What is the role of lysozyme in mucosal immunity?
🛡️ It breaks down bacterial peptidoglycan, especially effective against Gram-positive bacteria.
🛡️How does lactoferrin protect mucosal surfaces?
🛡️ It binds iron, making it unavailable for bacterial growth.
🛡️Name a key antimicrobial peptide and its function.
🛡️Defensins — they disrupt bacterial membranes.
🔬What cytokines do epithelial cells produce to recruit immune cells?
🔬 IL-8 (CXCL8) attracts neutrophils, while IL-1 and TNF activate inflammation.
🔬 What is xenophagy, and how does it work?
🔬A selective form of autophagy where epithelial cells engulf and degrade intracellular pathogens like Salmonella.
🧠 What receptor helps dendritic cells extend into the lumen to sample antigens?
🧠CCR6 — it helps guide dendritic cells to the epithelium.
🧠How do alveolar macrophages balance immune response in the lungs?
🧠They clear pathogens without triggering inflammation (to protect delicate lung tissue).
🧬 How is SIgA transported across epithelial cells?
🧬Plasma cells secrete dimeric IgA with a J chain.
Polymeric Ig receptor (pIgR) binds IgA and transports it via transcytosis.
The receptor is cleaved, forming the secretory component that protects SIgA from degradation.
🧬 What’s unique about IgG transport in mucosal immunity?
🧬 FcRn receptors (neonatal Fc receptors) transport IgG across epithelial barriers, especially in the lungs and placenta.
What is the role of Tregs (regulatory T cells) in mucosal immunity?
They promote tolerance to harmless antigens (e.g., food, commensals) by releasing IL-10 and TGF-β, preventing unnecessary inflammation.
What is “immune exclusion,” and how does it protect mucosal surfaces?
SIgA binds and traps pathogens in mucus, preventing adhesion and invasion without inflammation.
