Week 5 Flashcards
Fungal brain infection
C.albicans part of normal human commensal flora
Causes wide range of infections following disruption to immunity
Defence is mediated primarily by innate immunity carried by myeloid cells (includes neutrophils and macrophages)
Tissue resident macrophages are first responders to infection
Tissue resident macrophages are found everywhere
Often specialised to the organ e.g microglia in brain
Help in development
Many arise during embryogenesis and are not replenished by bone marrow
Pathogens are recognised by PRRs
Bind PAMPs
Main families of PRRs:
-TLRs signal via MyD88
-CLRs signal via CARD9
-NOD-like receptors
macrophages phagocytose the pathogen
Non-opsonised phagocytosis . PRR-PAMP binding
Opsonised phagocytosis. Antibody or complement binding
Phagosome fuses with lysosomes to form a phagolysosome leads to antigen presentation and pathogen killed.
Antigen presentation activates the active immune response, activation of T cells, antibody production etc
Gene expression- receptors can start activating transcription factors in nucleus of cell which transcribe to different genes
Cytokines
Small proteins signal to other immune cells
Proinflammatory (eg TNFa, IFNg)
Anti inflammatory (eg IL-10)
Help ‘direct’ an immune response
Many are called ‘interleukins’ IL followed by a number
Receptors often the cytokine name followed by R (eg IL-1R binds IL-1 cytokines
Chemokines
Mostly signal to immune cells and coordinate their movement in tissues
Either called CCL or CXCL followed by a number
Receptors are CCR or CXCR followed by a number
No set pattern between number of the chemokines and the receptors (eg CXCR4 binds CXCL12)
Activated macrophages make cytokines to promote inflammation
TNFa (pro-inflammatory cytokine): activates vascular endothelium; increases permeability brings more immune cells to site, fever (more difficult for microbes to grow)
IL-6: lymphocyte activation, boost antibody production. Fever, acute phase, protein production
IL-8: boosts chemotaxis, recruits neutrophils to site of infection
IL-1b: activates vascular endothelium, activates lymphocytes. Fever, production of IL-6
Chemokines form gradients
Tissue resident macrophages produce lots chemokines
at site infection
Other macrophage follows concentration of chemokines to area of infection
Chemotaxis
Chemotaxis brings inflammatory cells from the blood into the tissue
Rolling adhesion. Weak binding: leukocyte = carbohydrates, endothelium= selectins
Tight binding: leukocyte=integrins, endothelium= ICAMs
Diapedesis: immune cell moves inbetween endothelial cells into tissue
Migration
Leukocyte adhesion deficiency (LAD)
Primary immunodeficiency caused by mutations in adhesion molecules (integrins, selectins)
Leukocytes cant get from blood into tissue-> failure of chemotaxis
Different types depending on inherited mutation
Inability to make pus; belly-button inflammation (omphalitis)
Inflammatory mediators can help boost chemotaxis
Histamine
Prostaglandins: important for vasodilation, drive in inflammation
Leukotrienes: can act like a chemokines especially for neutrophils
Mast cells (innate immune cell): many granules packed full of histamine and other mediators. Granule release after activation (PRRs, pressure) driving Chemotaxis response
Neutrophils
Short lived (~2 days in blood)
Made in bone marrow
Numerous
Quickly infiltrate infected tissue
Granules
Highly phagocytic
Oxidative killing
Monocytes
Short lived (~2days in blood)
Made in bone marrow
Numerous
Quickly infiltrate infected tissue
No granules
Less phagocytosis and killing
Differentiate into macrophages once in tissues
The bone marrow makes more neutrophils during an infection
myeloblast-> promyelocyte-> myelocyte-> metamyelocyte-> band cell-> mature neutrophil
Cytokines have systemic effect on bone marrow to make more neutrophils
The bone marrow produces 1-2 10^11 neutrophils per day
Inflammatory mediators and complement proteins can regulate neutrophil production and their lifespan
Healthy person: WCC 610^9 neutrophils 4.5 10^9 CRP<3
ICU patient: WCC 3410^9, neutrophils 26*10^9, CRP 323
Causes of neutropenia
Not enough produced in bone marrow:
-aplastic anaemia
-blood cancers
-radiation
Autoimmunity
Chemotherapy
Circulating neutrophils not getting into tissue
Neutrophils kill pathogens
Especially bacteria and fungi
3 lobed nucleus ands granules
Neutrophil granules:
Primary (azurophilic):
-myeloperoxidase
-cathepsins
-defensins
-lysozyme
-elastase
Specific (secondary):
-lactoferrin (sequesters iron so microbes dont have all nutrients needed to grow)
-collagenase
Gelatinase (tertiary)
-gelatinase
-MMP9
Neutrophils use oxidative killing to make ‘bleach’ that kills pathogens
NADPH oxidase-> superoxide anions
Superoxide dismutase converts this into hydrogen peroxide
Myeloperoxidase MPO converts this into Hypochlorous acid effectively bleach
Failures in neutrophil killing:
- chronic granulomatous disease CGD cant activate NADPH oxidase
-MPO deficiency
-Chediak Higashi syndrome: phagosome cant mature because dont get fusion between lysosomes and phagosomes so don’t get full assembly of enzymes
Increased susceptibility to various infections
NETosis
A type of extracellular killing for large pathogens
Specialised cell death pathway
Neutrophils turn themselves inside out
Nuclear membrane breaks down, chromatin de condensation, DNA outside Cell covered in antimicrobial components, membrane rupture
NETs are sticky and can stop pathogens moving
NETs also full of toxic molecules and enzymes; damage to cell walls and membranes to burst pathogen cells
Key components of NETs:
-calprotectin
-histones/DNA
-antimicrobial peptides
-MPO
-elastase
What cells would you expect to find in the brain of a patient with a fungal infection
Neutrophils
What went wrong in patient with Brain fungal infection
Not enough neutrophils
Chemotaxis going wrong
Not making chemokines neutrophils wont move into tissue
Tissue resident macrophages only found in certain tissues in brain called microglia, 1st initiators of immune response so if defective wont see downstream response, only affect this tissue resident macrophages not ones in the liver or spleen for example
CARD9 deficiency
CARD9 is a signalling molecule that transmits signals from the CLRs (a type of PRR)
With no CARD9 the patients immune cells have defective innate recognition of fungi
Defective recognition means no chemokines production
No chemokines mean no neutrophil recruitment
No neutrophils mean the fungus can happily grow
Brain specific neutropenia
Original descriptions of inflammation
Rubor= redness= erythema
Tumor= swelling= oedema
Calor=heat
Dolor=pain
Causes of inflammation
What is inflammation: non specific response to tissue injury
-chemical agents
-cold, heat
-trauma
-invasion of microbes
Manifestation of the acute phase response
Why have inflammation:
-serves to destroy, dilute or wall off the injurious agent and induce repair
-but can be potentially harmful if uncontrolled
overview of the acute phase response
Recognise problem: danger signals by damaged tissues, recognised by innate immune cells
Response: cellular activation/recruitment. Cytokine/complement activation
Deal with problem: phagocytosis/destruction of pathogen. Resolution of inflammation or recruitment of adaptive immune response
Recognising the threat
Pathogen associated molecular patterns PAMPs are recognised by Pattern recognition receptors PRRs
PRRs are on every innate immune cell- extracellular and intracellular
Mast cell is the key innate recognition cell in the tissues
Mast cells initiate the acute phase response in tissues
Mast cells: live in skin and tissues
-detect injury
-release histamine and other mediators
-initiating inflammatory response
Basophils in the circulation
Basophil and mast cell contain similar granules
-activate the inflammatory response
-change vessel integrity to get cells from the circulation to the tissue
-activate cells
Histamine- increases capillary permeability
Heparin- anticoagulant
Eicosanoids- increases inflammation
Vasodilation, increased permeability, movement of white cells
Vasodilation: increased blood flow and pooling creating redness and warmth
Increased permeability: plasma proteins and cells extravasate creating swelling. Fluid loss into tissue leads to concentration of red blood cells and slowed blood flow (stasis) in vessels
Movement of white cells: blood stasis and activation signals leads to immune cells migrating towards offending agent
Physiology of the acute phase
Vasodilation—> erythema
Increased vascular permeability—> oedema
Cytokines—> heat
Mediators—> pain
Mediators of acute inflammation
Proteases:
-kinins (bradykinin)
-complement system
-coagulation/fibrinolytic system
Prostaglandins/leukotrienes:
-numerous metabolites of arachidonic acid
Cytokines/chemokines:
-TNF alpha, interleukins
-TGR beta, MCP
Arachidonic acid pathway
Lipoxygenase pathway:
-leukotrienes
-are Chemotaxins and vasoconstrictors
-cause increased vascular permeability and bronchospasm
Cyclo-oxygenase (COX) pathway:
-prostaglandins, prostacyclin and thromboxane
-cause vasodilation and prolong oedema
Blocking inflammatory mediators
Steroids- suppress everything
Antihistamine- useful in allergy to block histamine induced vasodilation
COX pathway inhibitors- NSAIDs/aspirin- block prostaglandins to reduce pain and fever, selective COX-2 inhibitors- celecoxib however these increase risk of stroke and heart attack. Blocking COX-1 can cause stomach irritation
Leukotriene inhibitors: used in asthma to reverse leukotriene induced bronchospasm
Acute phase cytokines
Local inflammation can cause/leads to systemic inflammation
An example of this is feeling systemically unwell when you have a chest infection
This is partially mediated by acute phase cytokines: IL-1, IL-6, TNF-alpha
Affect on:
-endothelium: vasodilation, increased permeability. Gets activated cells to the tissues
-hypothalamus: stimulates fever, decrease pathogen replication
-fat and muscle: protein/energy mobilisation, energy for fever and immune response
-liver: acute phase proteins eg increase CRP, opsonisation and complement activation
-bone marrow: neutrophil mobilisation, increased phagocytosis
- dendritic cells: TNF stimulates migration to lymph nodes and maturation, initiates adaptive response
Clinical consequences of blocking the acute phase
We use anti cytokine therapies to block the acute phase response
Anti TNF alpha - NICE approved for inflammatory bowel disease and rheumatoid arthritis
Anti IL-1 and anti IL-6- rheumatoid arthritis
Leukocytosis: leukocyte release results from a direct effect of IL-1 and IL-6 on bone marrow neutrophil stores. Exaggeration of this can result in a ‘leukaemoid reaction’ or left shift with release of immature precursors. Cause more damage than good
Overproduction of TNF-a and IL-1 can cause septic shock
Endotoxin (LPS) from gram negative bacteria (eg E.coli)
Blood circulation
Massive macrophage activation in liver and spleen
Overproduction of TNF-a and IL-1
Leads to dilation of blood vessels and massive leakage of fluid into tissues throughout the body. Widespread blood clotting (disseminated intravascular coagulation)
Leads to multiple organ failure/ septic shock
Fever
Abnormal elevation of body temp at least 1 degrees from normal 37C
May accompany inflammatory response
Release of pyrogens (agent that causes fever) such as interleukin 1, interferons or toxins from microbes, drug toxins, cancers
Target hypothalamus and cause release of prostaglandin E2
Raises temperature set point of hypothalamus
Fever why
Benefits of fever:
-inhibits reproduction of bacteria and viruses
-promotes interferon activity
-increases activity of adaptive immunity
-accelerates tissue repair
-increases CAMs on endothelium of capillaries in lymph nodes
-additional immune cells migrating out of blood
Risks of high fever:
-changes in metabolic pathways and denaturation of proteins
-possible seizures, irreversible brain damage when very high
Switching off inflammation
All mediators of acute inflammation are short lived
May be inactivated by enzymes eg heparinases
May be bound by inhibitors e.g. various anti-proteases
May be unstable e.g. some arachidonic acid derivatives
May be diluted in the exudate, e.g fibrin degradation products
Specific inhibitors of acute inflammatory changes
-e.g. lipoxins which block lipo-oxygenase pathway
Outcomes of acute inflammation
Complete restitution
Healing with scar formation
Abscess formation (encapsulation and pus)
Granuloma formation
Chronic inflammation
Chronic inflammation
When acute phase cannot be resolved:
-persistent injury or infection (ulcer, TB)
-prolonged toxic agent exposure (silica)
-autoimmune disease states (RA, SLE)
Mechanisms:
-cellular infiltration (granulomas)
-tissue destruction by inflammatory cells (COPD)
-attempts at repair with fibrosis and angiogenesis (new vessel formation)
Acute phase proteins in practice
Biomarkers that increase or decrease in response in injury, infection or inflammation
Acute phase proteins:
-CRP
-C3/C4
-fibrinogen
-ferritin
Negative control proteins:
-A1 antitrypsin
-albumin
-transferrin
acute phase proteins APPs have different kinetics
The main one we measure in practice is CRP because it goes up within 24hrs of acute phase response
Also settles very rapidly- allows us to see response to intervention eg. Antibiotics
CRP maps closely with infection rise and response so useful biomarkern
C-reactive protein CRP
Pathogen recognition molecule
-binds bacteria and fungal cell wall phospholipids
Opsonised pathogen and activates classical complement cascade by binding C1q (first component of classical pathway)
Goes up within 24-48 hours in response to:
-injury
-inflammation
-infection
Erythrocyte sedimentation rate
ESR= rate at which erythrocytes settle out of unclotted blood in one hour
Normally erythrocytes are very buoyant and settle slowly
Erythrocytes are negatively charged and repel eachother (no aggregation occurs)
In presence of acute phase reactants, erythrocytes aggregate due to loss of their negative charge resulting in increased sedimentation
Leukocytosis
Increased WBCs in blood
Leukocyte release results from a direct effect of IL-1 and IL-6 on bone marrow neutrophil stores
Exaggeration of this can result in “leukaemoid reaction” or left shift with release of immature precursors
