Immunology: Review of The Innate Immune System Flashcards
Why do we need both innate and adaptive immunity to protect us from infection?
- We need innate immuntity as it provides immediate and early protection against pathogens
- We need adaptive immunity as it provides ‘memory’ of an infection which makes it easier to recover next time we’re infected by the same/similar pathogen
- Innate immunity may not be enought to protect us from certain pathogens so adaptive immuntiy also needed
- Adaptive Immunity is too slow to protect us from some new pathogens
What’s the difference in specificity betwen innate and adaptive immunity?
- Adaptive immunity – Involves very specific recognition of infectious agent (usually sees an antigen on surface of pathogen)
- Innate immunity - Doesn’t involve specific antigen recognition but does involve recognition of broadly conserved features of different classes of pathogens
What are the components of innate immunity?
- Phagocytosis
- The Inflammatory Response
- Cytokines, Interferons and Antimicrobial peptides (AMPs)
- Complement
- Intrinsic Defences – “the hostile cell”
- Natural killer (NK) cells
What immune system cells carry out phagocytosis?
- Dendritic cells
- Macrophages
- Neutrophils
What role do dendritic cells have in innate immunity?
- Detect a pathogen, take it up and then stop any further phagocytosis
- They then move to lymph nodes where they break down the pathogen they’ve taken up
- They then present the pathogens peptides on its surface via MHC class II/I presentation which stimulates adaptive immune response
What roles do machrophages have in innate immunity?
- Phagocytosis - material is destroyed in lysosomes
-
Captured material can trigger macrophage activation - activated macrophages produce cytokines and chemokines to stimulate both innate and adaptive immune responses
- This triggers the inflammatory response and can promote a local anti-microbial state
- Involved in clearing and repairing damage
- NOTE: Most of them are tissue resident
What roles do neutrophils have in innate immunity?
- Rarely tissue resident - they’re circulating within bloodstream
- When there’s an infection they get recruited to site of infection/inflammation
- They carry out most of the phagocytosis
What is the inflammatory response?
- A generic defence mechanism whose purpose is to localize and eliminate injurious agents and to remove damaged tissue components
What things does the inflammatory response cause?
- Localised infection - stops pathogens frm leaving site of infection
- Removes pathogen via phagocytosis
- Repairs tissue damage from previous infection
- Enhances permeability of endothelium and extravasation
- Neutrophil recruitment
- Enhances cell adhesion - Makes cells sticky which prevents neutrophils from leaving
- Enhances clotting - Creates physical environment which makes it harder for pathogens to spread
What are cytokines?
- Glycoprotein hormones that affect the immune response
- Act as a very specific signal of a component of the immune response
- Have a very defined narrow role that helps immune system
- Act to modify the behaviour of cells in the immune response
- Most of these are called interleukins (eg. IL-1), some called interferons and TNF
What are chemokines?
- Glycoprotein hormones that affect the immune response
- Secreted at site of infection like chemokines
- Act as chemotactic factors – they create concentration gradients which attract (or occasionally repel) specific cell types to a site of production/infection
How do phagocytes know what targets to phagocytose?
- By detecting phosphatidylserine on exterior membrane surface - Indicates cells undergoing apoptosis as phosphatidylserine located on inside of healthy cell
- By Scavenger receptors -
- By some Toll-Like Receptors (TLRs) - Play very little role in recogniation of material to be phagocytosed
- By passive sampling - At site of infection cells phagocytose things at random (mainly done by neutraphils)
What are PAMPs?
- PAMPs = Pathogen-associated Molecular Patterns
- Molecules present only on pathogens and not on host cells
- Essential for survival of pathogens
- Invariant structures (can’t be changed) tahte are shared by entire class of pathogens
What are some examples of PAMPs?
- Gram-negative bacteria - All have lipopolysaccharides (LPSs) found in outer membrane
- Gram-positive bacteria - All have teichoic acid, lipoteichoic acid and peptidoglycan found in outer membrane
- Bacterial flagella
- Abnormal protein glycosylation
- Abnormal nucleic acids - viral nucleic acid slightly different to host cell nucleic acid
What are pattern recognition receptors (PRRs)?
- Host factors that specifically recognise a particular type of PAMP
- They are germ-line encoded - always express the exact same thing in whatever cell they are expressed in