Inflammation Flashcards
What are the four cardinal signs of inflammation?
Heat, swelling, redness and pain
What is pus?
Accumulation of fluid, living and dead white blood cells (neutrophils), dead tissue, and bacteria or other foreign invaders or materials.
What is an abscess?
Localized collection of pus in any part of the body, often caused by an infection by pyogenic bacteria.
Associated with liquefactive necrosis of related solid tissue.
What initiates inflammation?
Presence of PAMPs and DAMPs which activates resident cells
How do resident cells (i.e dendritic cells and macrophages) respond to PAMPs and DAMPs?
Bind to PRRs cells secrete cytokines and chemical mediators
What do the chemical mediators and cytokines released by DCs do?
Lead to vasoactive substance release which leads to the release of inflammatory exudate from post-capillary venules
What cells and proteins does inflammatory exudate contain?
Rapidly recruited to sites of injury: Platelets and Neutrophils (PMN)
Recruited soon afterwards to sites of injury: Monocytes ( become Macrophages), T- Lymphocytes
Recruited to sites of allergic inflammation: Eosinophils / Basophils
Albumin
Antibodies
Complement proteins
Coagulation factors
Acute phase PRRs?
Mannose Binding Lectin (MBL)
C-Reactive Protein (CRP)
Intracellular PRRs?
Protein Kinase PKR (dsRNA activated)
2’-5’ oligoadenylate synthase (OAS)
NOD, RIG and some TLR (TLR-9) proteins
Macrophage receptors?
Macrophage Mannose Receptor (MMR)
Macrophage Scavenger Receptor (SR-AI & SR-AII, MARCO)
Dectin-1 (β-glucan receptor)
Toll-like Receptors (TLRs)
What is the role of scavenger receptors?
Scavenger receptors mediate uptake of modified LDL by macrophages to give foam cells
Both SR-AI and SR-AII bind a wide range of polyanionic ligands
Acetylated & oxidised LDL not native LDL
Gram negative and Gram positive bacteria
Asbestos, silica, LPS, LTA, AGE-modified proteins
What is the role of Dectin-1?
Major macrophage (Mφ) receptor for β-glucan
β-glucan is a major component of fungal pathogen cell walls
What is the role of TLR4?
TLR-4 responds to the LPS PAMP.
TLR4 signalling inside Mφ involves the proteins Myd88 and IRAK-4.
How does TLR4 detect LPS?
LPS transport in plasma is mediated by the protein LBP, LBP transfers LPS to the Mφ CD14 receptor, CD14 facilitates TLR4 recognition of LPS. This requires a small protein bound to TLR4 - (MD-2)
What does LPS treatment of Mφ stimulate secretion of?
TNF-α, IL-1, IL-6, and inflammatory mediators such as chemokines.
What does TLR5 respond to?
TLR5 responds to the flagellum protein flagellin.
What are some examples of what TLR2 can respond to?
TLR2 recognises Staph aureus peptidoglycan and lipoproteins
TLR2 recognises GPI anchors on membrane proteins of Trypanosoma cruzi
TLR2 recognises lipoarabinomannan from Mycobacterium tuberculosis
TLR2 can also recognise zymosan from yeast cell wall
What does TLR9 recognise (be specific)? How does it signal?
Identifies presence of bacterial DNA, categorised by unmethylated CpG dinucleotides
TLR 9 lies intracellularly, once activated, it moves from the endoplasmic reticulum to the Golgi apparatus and lysosomes, where it interacts with MyD88
What is the inflammasome important for protection against?
Intracellular pathogens
How is the inflammasome activated?
TLR signalling leads to NFKB stimulations, leads to transcription of a large number of genes in response to inflammatory stimuli
These mRNA are translated into protein for pro-IL-1B and caspases.
Proteins could be secreted, but must be first cleaved by active cysteine protease (caspase)
Inactive NLRP3 inflammasome activated
What is released upon inflammasome activation?
IL-1beta, IL-18
What can activation of the inflammasome lead to?
Pyroptosis
What drives DNA synthesis, granule biogenesis and growth of neutrophils?
GM-CSF and G-CSF
What are the neutrophil stages of development?
Myeloid precursor (myeloblast) Progranulocyte Myelocyte Band neutrophil (nucleus not yet defined into lobes) Mature neutrophil
What % of WBC are PMNs?
40-70% (~50%)
Reasons for increased PMN count?
Physiological: Exercise, stress, adrenaline
Infection: Bacterial infection, some fungal and parasite
Inflammation:Burns, vasculitis, myositis, necrosis
Metabolic disease:Gout, ketoacidosis, uremia
Other: Haemorrhage, tumours, haemolysis
Reasons for decreased PMN count?
Failure of production: Bone marrow failure (aplastic anaemia)
Accelerated destruction: Immune mediated PMN destruction, splenomegaly
Idiopathic: Irridation, chemotherapy
Other: Genetic disease (Kostmann/severe congenital neutropenia)
What are the successive stages of neutrophil migration?
Margination Leukocyte rolling Activation and tight adhesion Diapedesis (extravasation) Chemotaxis
Why does neutrophil margination occur?
Vasoactive substances cause vasodilation of small venules, and rouleaux of red cells - slower blood flow allows the leukocytes to travel in the periphery of the lumen so they can interact with the vascular endothelium
Describe leukocyte rolling
Both endothelial cells and neutrophils are induced to express selectins (by inflammatory cytokines), E and P selectins on the endothelium adhere to Sialyl-Lewis X glycoprotein on the neutrophil or monocyte which then begin to roll along the endothelium.
Low affinity interactions
How are leukocytes activated and tightly adhered to the vessel?
Binding of chemokines to GPCRs on the cell surface
Alters the surface expression of integrins allowing them to form tight interactions with receptors on the endothelium - arresting its rolling.
These include ICAM-1, which is induced by TNF-α and upregulated by NF-κB.
How does diapedesis occur?
Neutrophil/monocyte will cross the endothelial wall by squeezing between adjacent cells and penetrating the basement membrane with the aid of elastase enzymes
What is chemotaxis?
Released neutrophils and monocytes move by chemotaxis, following a concentration gradient of chemokines produced classically at infection sites
What is the role of beta 2 integrin?
Interacts with ICAM to halt leukocyte rolling/lack of B2 (CD18) causes Leukocyte Adhesion Deficiency
What does bacterial peptide fragment fMet-Leu-Phe bind to?
Human receptor FPR1 to initiate innate response, potent neutrophil chemoattractant
During acute inflammation macrophages accumulate before neutrophils
True
Macrophages have a short lifespan in normal tissues
False
During acute inflammation macrophages are the major source of TNF-alpha
True
Bacterial killing by macrophages does not involve a respiratory burst
True - only neutrophils
Macrophages are stimulated to divide following exposure to antigen
False
What are opsonins?
Serum factors that make bacteria more palatable to leukocytes, without them, phagocytosis progresses far more slowly.
Some examples include; IgG antibody, Complement C3b, surfactant proteins A&D, C-reactive protein (CRP).
What anti-microbial contents do the neutrophil granules contain?
Oxygen independent bactericidal compounds (enzymes and antimicrobial peptides)
Oxygen dependent radicals.
What is respiratory burst?
Respiratory burst is the phenomenon in which the rapid release of ROS causes bacterial death.
How are superoxide radicals synthesised?
Cells catabolise glucose to NADPH, leading to the assembly of NADPH oxidase. This enzyme produces a superoxide radical which can then convert to H2O2.
What radicals have the highest bactericidal function?
Halogens and hydroxyl radicals
What is NETosis?
Unique form of cell death, where neutrophils to release extracellular DNA traps, composed of decondensed chromatin, histones, and granule proteins. These traps form an extracellular fibril matrix which traps organisms so they can be more effectively phagocytosed.
What are the two origins of macrophages?
Embryonic yolk sac derived tissue macrophages - these are self renewing and long lived.
Tissue residents of blood monocytes - recruited to tissues when cytokines signal.
What is the role of yolk sac macrophages?
They constantly patrol tissues so are often the first WBC that responds to infection.
Two types of macrophages?
M1 (classically activated) macrophages are proinflammatory, they promote T cell immunity, and secretion of vasoactive cytokines
M2 (alternate activation by endotoxin, IFN-gamma, IL-4/13) macrophages are anti-inflammatory, although they can be important in asthma, M2 macrophages play a pathological role in tumourgenesis.
What cytokines do M1 macrophages release?
TNF-α, IL-6 and IL-1β.
Total WBC count: 25 x 109 cells/L (v high) Neutrophils: 20% (low) Lymphocytes 76% (very high) Monocytes: 3% (low) Eosinophils 1% (low) Basophils: 0%
Acute viral infection
Total WBC count: 11 x 109 cells/L (higher than normal) Neutrophils: 85% (High) Lymphocytes 11% (Low) Monocytes: 3% (low) Eosinophils 1% (low) Basophils: 0%
Acute bacterial infection
Total WBC count: 3 x 109 cells/L (low) Neutrophils: 9% (very low) Lymphocytes 83% (very high) Monocytes: 7% Eosinophils 2% Basophils: 1%
Chronic viral infection
Type I interferons induce lysis of enveloped viruses
False
Type I interferons activate macrophages to kill intracellular parasites
False
Type I interferons inhibit viral protein synthesis in infected cells
True
What are prostaglandins (origin)?
Products of lipid metabolism
Tumour necrosis factor (TNF)-alpha is a major mediator of septic shock
True
Endotoxin stimulates TNF-alpha production by B lymphocytes
False, endotoxin stimulates TNF-alpha production by macrophages
Non-steroidal anti -inflammatory drugs work by blocking histamine H1 responses
False (work by blocking action of COX-1)
Interleukin-1 (IL-1) is a potent mediator of fever
True (it produces fever)
The spleen is a major site for synthesis of acute phase proteins
False (produced by liver)
C Reactive Protein (CRP) is an acute phase protein
True
Where are complement proteins synthesised?
Liver
Alternative complement activation
Alternative pathway: the response activated by C3 (complement 3 plasma protein)
Initiated by hydrolysis of C3 into C3(H2O), environment around pathogens stimulates this change.
C3(H2O) binds to factor B making it susceptible to cleavage by factor D.
The reaction produces Ba and Bb fragments.
C3bBb is a protease that promotes cleavage of C3 into C3a and C3b.
What complement pathway is the first to act?
Alternative
What do factor B and D do (complement)
C3 binds factor B, factor B can be cleaved by factor D
Lectin complement activation
Mannose binding lectin (MBL) binds to the pathogen surface
Generate C3 convertase C4b2b that promotes cleavage of C3 into C3a and C3b.
What complement pathway is the last to act?
Classical
Classical complement activation
IgM/IgG antigen complex activates C1
C1s cleaves C4 and C2 to generate C4b and C2b
C4b2b is an active C3 convertase which promotes cleavage of C3 into C3a and C3b.
What are the three outcomes of complement?
Opsonisation of particles for phagocytosis - C3b is opsonin
C5a as a chemoattractant - C5a also acts as an anaphylatoxin.
Membrane attack complex (MAC) - Assembly of a multi protein complex in the pathogen membrane called the MAC attack complex.
Which of the inflammatory mediators are generated from arachadonic acid?
Prostaglandin, Thromboxane or Leukotriene (all from arachidonic acid)
What is the kallikerein kinin system?
Involved in inflammation, blood pressure control, coagulation and pain.
It is dependent on the generation of Bradykinin, a potent vasodilator and Plasmin, which degrades blood clots during fibrinolysis.
How to proinflammatory cytokines upregulate coagulation?
Upregulating the coagulation cascade.
Widespread intravascular fibrin deposition, which appears to be a result of enhanced fibrin formation and impaired fibrin degradation.
Enhanced fibrin formation is caused by tissue factor-mediated thrombin generation and simultaneously occurring depression of inhibitory mechanisms, such as the protein C and S system.
The impairment of endogenous thrombolysis is mainly due to high circulating levels of PAI-1, the principal inhibitor of plasminogen activation.
What is the role of CRP?
Recognises pathogens binding to bacterial LPS – this has a dual action:
Opsonising the bacterium and thus enhancing macrophagic function
Interacting with C1q stimulating the classic complement pathway.
Sequence of key events in septic shock
LPS (Gram negative bacterial endotoxin) binds monocyte CD14 receptor - TLR4 signalling
Systemic TNF-α, IL-1, IL-6 & IL-8
Fever, endothelial damage, capillary leakage, hypotension
Systemic activation of coagulation cascade (DIC) (microvascular thrombosis)
Hypoperfusion
Multiorgan System Failure (fibrin deposition and hypoxia)
IFN gamma
Leads to macrophage activation
