Epithelial Barriers & Non-Specific Defences
What is one physical feature of epithelial surfaces that prevents microbial entry?
Tight junctions between epithelial cells
What are two hallmark signs of acute inflammation?
Redness (rubor) and swelling (tumor)
Which two cell types are the primary phagocytes in innate immunity?
Neutrophils and macrophages
What is the general function of antimicrobial peptides?
To directly kill or inhibit the growth of microbes
Which type of cells do NK cells not kill and why?
Healthy self-cells, because they express normal levels of MHC class I, which sends an inhibitory signal to NK cells preventing cytotoxic action.
Which enzyme in tears and saliva breaks down bacterial cell walls?
Lysozyme
Which cytokines are released early during inflammation to recruit immune cells?
TNF-α, IL-1, IL-6
What is the first step in phagocytosis after recognition of a pathogen?
Engulfment / Formation of a phagosome
Name a well-known family of antimicrobial peptides found in neutrophils and epithelial cells.
Defensins
How do NK cells detect infected cells?
By detecting low MHC I expression and stress-induced ligands
Name one chemical barrier secreted by the skin that deters microbial growth.
Fatty acids / Sebum / Antimicrobial peptides (like defensins)
What causes the redness and heat in inflamed tissues?
Increased blood flow due to vasodilation which is caused by the degranulation of mast cells.
What role do opsonins like C3b play in phagocytosis?
Enhance pathogen recognition and binding by phagocytes
What is the respiratory burst and which cell uses it?
A rapid release of ROS by neutrophils and macrophages
What cytotoxic molecules do NK cells release to kill infected cells?
Perforin and granzymes
What role does mucus play in non-specific defence?
Traps microbes and facilitates their clearance via ciliary action
What is the role of histamine in the inflammatory response?
Increases vascular permeability and vasodilation
What intracellular organelle fuses with a phagosome to kill pathogens?
Lysosome (forms a phagolysosome)
What are two reactive oxygen species generated by phagocytes?
Superoxide (O₂⁻), Hydrogen peroxide (H₂O₂)
What is the role of C5a in the complement cascade during inflammation?
C5a acts as a powerful chemoattractant, recruiting neutrophils and other immune cells to the site of infection and also increases vascular permeability.
How does the microbiota of epithelial surfaces protect against infection?
Competes with pathogens for nutrients and space; produces antimicrobials
Describe the steps of leukocyte recruitment from the bloodstream to the site of infection.
Leukocytes are recruited through five key steps: rolling (via selectins), activation (by chemokines), firm adhesion (via integrins), transmigration through the endothelium (diapedesis), and chemotaxis toward the infection site.
How do dendritic cells link phagocytosis to activation of the adaptive immune response?
By presenting antigens to T cells via MHC molecules
How do ROS and antimicrobial peptides work together in intracellular killing?
ROS damage microbial membranes/DNA; peptides form pores in pathogens
What happens when the membrane attack complex (MAC) is formed?
It creates pores in pathogen membranes, leading to cell lysis