Lec 3- innate immunity part 2 Flashcards
Inflammation
-Complex, multifactorial response to infection, damage, trauma
-Beneficial
-It is not synonymous with infection
-Can be sterile
Cardinal signs: heat, pain, redness, swelling and loss of function
Acute inflammation
- Local reaction
- Movement of proteins and cells from blood to tissue
- Predominantly neutrophils
- Clearance of immune challenge
- Resolution: poorly studied
- Maybe pus- (contains neutrophils carrying myeloperoxidase)
- When acute inflammation containing pus doesn’t come to a point, the core of the abscess isn’t cleared so has to be drained via surgery, this is known as granulomas
Kinetics of acute inflammation
- There are lots of different cytokines and chemokines
- Within 1 hour of infection neutrophils start to increase
- After 6 hrs apoptosis increases this is because the neutrophils fight and DIE
- Around 24hrs later there is an increase in mononuclear cells these are the macrophages which engulf the dead neutrophils
Chronic inflammation
- Prolonged
- Non-resolving
- Leads to loss of function
- Persistent inflammatory cells and mediators
- e.g. RA
Cells of innate immunity recognises pathogens- pattern recognition
- Pattern-recognition receptors (PRR) bind to pathogen-associated molecular patterns (PAMP’s)
- Mannose R, scavenger R, Glucan R are all lectin (links to the lectin pathway of C3 activation) and recognise carbohydrates on microbial surfaces
- CR3 bind iC3b (from complement activation) and LPS
- CD14 binds LPS (lipopolysaccarides)
- All binding leads to phagocytosis
Toll-like receptors (TLR) sense infection
TLR
- Family of signalling receptors
- Expressed by different cells types
- Recognise different pathogens
- Tailor innate immune response to WHAT and WHERE
- TLR signalling switches on cytokine production: informs adaptive immunity
- Has a pathogen recognition domain
TLR’s sense infection
- The receptor location will give a good indication to what type of microbe it will act on
- e.g. microbes that will act on the outside of cells such as bacteria, fungi and parasites will be on the plasma membranes
- The receptors on the endosomes (inside the cells) will effect virus’
Pathogens induce cytokine release
SE= systemic effects
LE= local effects
-On sensing microbial production, macrophages secrete a variety of pro-inflammatory cytokines e.g.
IL-6:(SE) Fever; induce acute phase proteins production by hepatocytes
TNF-a: LE- activates vascular endothelium and increases vascular permeability which leads to increased entry of complement and cells to tissue and increased fluid drainage to lymph nodes; SE- fever (pyrogens), mobliz`tion of metabolites, shock
IL-1b: LE- activates vascular endothelium, activates lymphocytes, local tissue destruction increases access of effector cells; SE- Fever, production of IL-4
CXCL8- LE- chemotactic factor recruits neutrophils and basophils to site of infection
IL-2- LE- activate NK cells
Neutrophils are recruited to sites of infection
- Neutrophils- most abundant white cells: 50 billion in healthy children; short lived around- 2 days
- Huge bone marrow reserves of mature neutrophils
- Production of inflammation attracts neutrophils to sites of infection
- Neutrophils are adapted for working without oxygen
- They will die hours after entry to infected tissue- forming pus (myeloperoxidase)
Neutrophils roll, bind and migrate
1) Rolling adhesion
- It binds to the 1st receptor
2) Tight binding
- then binds to LFA-1/ICAM-1 receptor will slow this down further allowing it to bind to cytokines
3) Diapedesis
- This is the movement of the cell through the endothelial membrane
4) Migration
- Moves into the cell and now starts producing more cytokines meaning that it attracts more neutrophils
Complement components promote inflammation
- Anaphylatoxins act on blood vessels to increase vascular permeability (C3a and C5a)
- Increased permeability allows increased fluid leakage from blood vessels and extravastation of complement and other proteins at the site of infection
- Migration of monocytes and neutrophils from blood to tissue is increased
- Microbicidal activity of macrophages and neutrophils is also increased
Mast cells
- C3a and C5a activate mast cells: anaphylatoxins
- Resident in tissue and sub mucosal
- Release of vasoactive amines e.g. histamine
- Release of cytokines e.g. TNF-a
- Recruits: Ab, complement, fluid (Helps APC drain), cells
Process in local inflammation
- A cut in the skin and microbes enter through the cut
- Complement activation occurs
- Macrophages move into the space partly by chance and partly by complement and start the process of phagocytosis
- Macrophages release cytokines and chemkines
- Complement then activates mast cell to degranulate causing release of inflammatory mediators
- Inflammatory mediators, cytokines and chemokine all act on nearby blood vessels to present receptors to causing migration of neutrophils
- Neutrophils then pass to kill bacteria
Inflammatory mediators
-Cytokines
-Chemokines
-Complement
-Amines
-Lipid mediators e.g.
Eicosanoids (20C chain) e.g. PG’s LT’s and lipoxines
Produced from arachidonic acid by COX-1 and 2 but also lipo-oxygenase
Neutrophils are good eaters
Similar mechanism to macrophages
-PPR and CR
-Unopsonised and opsonised pathogen recognised
-Greater diversity of diet than macrophages
-More antimicrobial weapons than macrophages
Phagosomes fuse with azurophillic (primary) granules and specific (secondary) granules- these contain various enzymes, anti-microbial, toxin
Death comes swiftly
They eat and die
- bacterium is phagocytosed by neutrophils
- Phagosomes fuses with azurophillic (primary) and specific granules
- pH of phagosomes rise, antimicrobial response is activated, and bacterium is killed
- pH of phagosome is decreased, fusion with lysosomes allow acid hydrolases to degrade the bacterium completely
- Neutrophil dies by apoptosis and is phagocytosed
Pathogens die by oxygen-independent and oxygen dependant mechanisms
Oxygen-Independent:
-Lysozymes, defensives, cathepsin G, elastase are all found in azurophillic granules
-Lactoferrin, enzymes and NADPH oxidase components are found in specific granules
Oxygen-dependant
-Assembly of active NADPH oxidase at membrane results in respiratory burst and produces powerful oxidising agents- superoxide H2O2
-This alters pH in phagosome to activate protease (high pH) and acid hydrolases (low pH)
Neutrophils are vital for effective immunity
Chronic granulomatous disease (CGD)
- Mutations in genes for NADPH oxidase
- No respiratory bursts
- No pH change in phagosome
- No damage to pathogens
- Infections are not cleared and remain in localised nodules- granulomas
Inflammatory cytokines multi-task
-IL-1, IL-6 and TNF-a are released by macrophages in to bacteria
-These have multiple effects on the body
Including increased temperature; reduced bacterial and virus growth; enhance adaptive immunity
-They stimulate the production of acute phase proteins: C-reactive protein (CRP) (classical pathway)and mannose binding lectin (lectin pathway)- these are 2nd response of innate immunity
Acute phase proteins enhance innate immunity
- Bacteria induce macrophages to produce IL-6, which acts on hepatocytes to induce synthesis of acute-phase proteins
- This causes CRP binds to phosphocholine on bacterial surfaces, acting as an opsonin and as a complement activator
- It Also causes mannose binding lectin binds to carbohydrates on bacterial surfaces, acting as an opsonin and as a complement activator
- CRP binds to bacterial and fungal cell wall
- MBL binds to mannose containing carbohydrates
- Both are opsonins
- Synthesis increases 1000 fold in the acute phase response
Complement activation by MBL and CRP
- MBL sticks to the pathogen surface
- This molecules contains enzymes on the top of it which is a C4 convertase
- This converts C4 into C4a and C4b and C4b attaches to cell surface
- The enzyme is also a C2 convertase and so turns C2 into C2a and b
- C2a attaches onto C4b; C4bC2a is a C3 convertase
- This is the same as complement
- CRP is the same but the CRP is attached to phosphocholine and to the pathogen surface
- C1 then binds to the top of CRP
- This then turns into C4 convertase
Complement activation has different initiations but the same end results
-3 activation pathways- Alternative, classical and lectin
-All 3 pathways converge at production of the C3 pathways
-Activation pathways differ with time:
+At the start of an infection, mainly alternative pathway (C3 fixation i.e. complement)
+Acute phase response produces CRP and MBL- lectin and classical pathway
Innate defence against virus: the interferon response
- Virus infected cell
- IFN-a and IFN-b response
- Induces resistance to viral replication in all cells
- Increase expression of ligand for receptors on NK cells
- Activate NK cells to kill virus-infected cells
Natural killer (NK) cells
- NK cells are the killers of innate immunity
- Large granular lymphocytes
- NK are the cytotoxic T cells of innate immunity- kill and make cytokines
- Activity increases 20-100 times on exposure to the IFN
- NK provide an early response to virus infection- until cytotoxic T cells are ready
- People with no NK cells- persistent viral infections despite normal adaptive immune response
NK cells use their receptors to distinguish between healthy and sick cells
- In normal cell there is a normal ligand, when a NK cell binds to this it sends inhibitory signals meaning the normal cell won’t be killed
- When cell is infected with a virus it will place another ligand on the cell surface,
- The NKG2D receptor binds to the ligand on the infected cell]
- This will send Positive signals to the NK cell causing the cell to be destroyed
