The induced response to infection (1) Flashcards
What do cellular receptors of innate immunity do?
They distinguish ‘non-self’ from ‘self’
What do macrophages carry?
A battery of phagocytic and signalling receptors
What do toll-like receptors do?
Sense presence of 4 main groups of pathogenic microorganisms
What receptor recognises LPS?
TLR4
What does recognition of LPS by TLR4 do to macrophages?
Changes macrophage gene expression
What does genetic variation in TLR do?
Associated with resistance or susceptibility to disease
What happens when resident macrophages are activated?
A state of inflammation is initiated at site of infection
How do inflammasomes amplify innate immune system?
They increase production of IL-1beta
Which cells are first effector cells recruited to sites of infection?
Neutrophils
What do inflammatory cytokines do?
They recruit neutrophils from blood to infected tissue
What happens to neutrophils after they consume pathogens?
They destroy themselves and release cytokines
What do inflammatory cytokines do?
They raise body temperature, activate liver to make acute-phase response
How many phases to human immune response?
3
What happens during the immediate innate immune response?
Pathogen invades tissue and proliferates.
Pathogen is recognized by preformed soluble effector molecules and resident effector cells in the infected tissue
Pathogen is either eliminated or the induced innate response is triggered
How long is the immediate innate immune response?
0 - 4 hours
What happens during the induced immune response?
Pathogen invades tissue and proliferates
Activation of cells resident in the infected tissue. Recruitment of effector cells to the infected tissue. Inflammation, fever, the acute phase response.
Soluble effector molecules and effector cells recruited to infected tissue recognize and attack pathogen.
Pathogen is either eliminated or survives and instigates the adaptive immune response
What are innate recognition receptors that recognize pathogens?
Pathogen Recognition Receptors (PRRs)
Which cells express PRRs?
Macrophages, NK cells, and other cells of innate immunity
What do PRRs recognize?
Carbohydrates, lipids, proteins nucleic acids typically found on pathogenic surfaces
How do innate immune cells recognize self and non-self cells?
Pathogen Associated Molecular Patterns (PAMPs)
Damage Associated Molecular Patters (DAMPs)
What are PAMPs?
Shared molecular structures on microbial surfaces (eg. LPS)
What do DAMPs?
Damage to self-cells
How many receptors are there for PAMPs/DAMPs?
> 100
What do PRRs recognize?
PAMPs and DAMPs
How many receptors can engage with bacterium at same time?
Many
What do NK cells recognize?
Virally infected cells by recognizing changes at surface of human cells
What do resident macrophages have to recognize invading pathogens?
Phagocytic receptors which bind invaders and trigger phagocytosis
Signalling receptors that bind to pathogen and then instruct macophages to recruit additional cells to infected site
What type of receptors are phagocytic and signalling receptors on macrophages?
PRRs
What is the ligand for mannose receptor?
LPS, CPs
How are microorganisms phagocytosed by phagocytes?
Phagocytes contain receptors on surface that recognize components of microbe surface
Microorganisms are bound by phagocytic receptors on macrophage surface
Microorganisms are internalized by receptor-mediated endocytosis
Fusion of endosome with a lysosome forms a phagolysosome in which microorganisms are degraded
What are Toll-like receptors?
A family of 10 phagocyte signalling PRR receptors with variable specificity for a range of pathogens
How are Toll-like Receptors named?
TLR1 - TLR10
What shape and structure do TLRs have?
Horseshoe shape on outside surface (rich in leucine rich repeats (LRR) and a Toll-interleukin receptor (TIR) on the cytoplasmic side.
TLRs work in pairs as homodimers (2 of same type) or heterodimers (2 different TLRs come together)
What amino acid are TLRs rich in?
Leucine
What does the TIR domain do?
It activates response of TLRs
What is another name for TLRs?
CD281 - CD290
Are all TLRs facing the extracellular space?
No, some can face inside of endosomes.
What is the purpose of intracellular TLRs?
To recognize intracellular pathogens
Which TLRs form homodimers?
TLR3
TLR4
TLR5
TLR7
TLR8
TLR9
TLR10 (can also form heterodimer with TLR1 and 2)
Which TLRs form heterodimers?
TLR1:TLR2
TLR1:TLR10
TLR2:TLR6
TLR2:TLR10
What does TLR4 recognize?
LPS
Which pathogens typically have LPS?
Gram-negative bacteria (Remember outer membrane)
Which immune cells express TLR4?
Macrophages
Dendridic cells
Mast cells
Eosinophils
What does TLR3 recognize?
Double stranded viral RNA
Which cells express TLR3?
NK cells
Where are TLR3 receptors located? Why?
On endosomes, they recognize double stranded viral DNA and are signalling receptors.
This is a great way to recognize viruses and alert the immune system about the presence of viruses.
What does TLR4 work with to recognise LPS?
It forms a complex with TLR4, MD2, and CD14 at cell surface.
How does the TLR4, MD2, and CD14 complex bind LPS?
Complex is assembled binding LPS on macrophage surface.
TIR is expressed and it creates a signalling cascade which leads to NFkappaB activation which is a transcription factor that instigates cytokine release.
(TIR - MyD88 –> IRAK4 –> TRAF6 –> kinase cascade –> IKK –> NFkappaB –> degradation of IkappaB resulting in transcription of cytokines)
What are LBPs?
LPS Binding Protein mediated transport down to receptor complex (TLR4-MD2-CD14)
What does IkappaB do?
It is always bound to NFkappaB until it is degraded by binding of LPS to TLR4-MD2-CD14 complex and the triggering of the kinase cascade
What happens if there is a mutation in NFkappaB activation due to lack of IKKgamma?
Results in immunological and developmental defects. (X-linked ectodermal dysplasia and immunodeficiency)
Unusual physical features also develop such as conical or missing teeth
What are cytokines?
Short-lived molecules that exert influence within short distance from where they were made.
Signalling proteins which bind to cytokine receptors and induce intracellular signalling that change behaviour of second cell
What do inflammatory cytokines do?
Act to create state of inflammation
What do chemokines do?
Attract immune cells away from blood towards infected area
What are the 5 most important cytokines that a macrophage makes?
IL-1beta
TNF-alpha
IL-6
CXCL8
IL-12
What do IL-1beta and TNF-alpha do?
Induce blood vessels to become more permeable (more effector molecules can enter the infected tissue)
What does IL-6 do?
Induces fat and muscle cells to metabolise and make heat to raise body temperature and create heat and raise temperature in infected tissue
What does CXCL8 do?
Recruits neutrophils from blood into infected tissue
What does IL-12 do?
Recruits and activates NK cells that in turn secretes cytokines that make macrophages’ response even stronger to infection
What do IL-1beta, TNF-alpha, IL-6, CXCL8, and IL-12 collectively do?
They create a state of inflammation at site of infection
What type of molecule is CXCL8?
It is a conformation of chemokine
What are NOD-like receptors (NLRs)?
Receptors that detect products derived from intracellular degradation of phagocytosed pathogens
What is the structure of NLRs like?
Receptors that detect products derived from intracellular degradation of phagocytosed pathogens
What does NOD1 do?
Recognizes gamma-glutamyl diaminopimelic acid of gram-negatives
What does NOD2 do?
Recognizes muramyl dipeptide of most bacteria
How do NLRs recognize pathogen domains?
Leucine Rich Regions (LRRs)
Central nucleotide-binding oligomerisation domain (NOD)
Caspase-recruitment domain (CARD) at amino-terminal side
What do NLRs do after binding to bacterial antigens?
They dimerise, bind kinase RIPK2
NLR bound -> NLRs dimerise -> bind kinase RIPK2 -> RIPK2 phosphorylates kinase TAK1 -> cascade of reactions leading to activation of NFkappaB -> transcription of cytokines
What is the inflammasome?
It is formed by oligomerisation of NLRs.
How do inflammasomes amplify innate immune response?
They produce IL-1beta
What is important to know about IL-1beta?
It is hugely potent and can make you pretty sick so it must be tightly regulated.
What ensures the right production of IL-1beta at the right time?
NLRs and the inflammasome
How is the inflammasome produced?
NLRP3 comes together with adaptor protein and procaspase 1 (which cleaves pro-IL-1beta to activate it.
This can only happen once inflammasome is produced after oligomerisation of NLRs and procaspase 1 and adaptor protein.
In what form is IL-1beta produced?
Inactive form which must be cleaved to function
Which cells produce IL-1beta?
Activated cytokines
What type of feedback mechanism do activated macrophages use to produce IL-1beta?
Positive feedback
What domain is shared between TLRs and IL-1 receptor?
They both share the same TIR signalling domain
What cytokines are activated by the inflammasome?
IL-1beta
IL-18
What changes instigate oligomerisation of NLRs into inflammasome?
Ionic change in cytoplasm
How do neutrophils enter the inflamed tissue and leave the bloodstream?
IL-8/CXCL8 bind to receptors on neutrophil causing it to bind to surface of blood vessel via complementary pairs of adhesion molecules; one which is on leukocyte surface and another on tissue cell surface.
How do neutrophils move through blood when there is no infection?
Neutrophils travel rapidly through blood without interacting with vascular endothelium
How do neutrophils roll around on blood vessel walls prior to extravasing at site of inflammation?
Cytokines induce expression of selectin on vascular endothelium which enables leukocyte binding.
Neutrophils express sialyl-LewisX
sialyl-LewisX (s-LeX) on leukocyte form transient interactions with selectin on endothelium causing neutrophils to “roll”
What happens to blood vessels during inflammation and why?
Blood vessels dilate and blood flow decreases so neutrophils can interact with vessel walls, extravasate, and migrate to infection site.
How do neutrophils extravasate?
Rolling adhesion
Integrins on leukocyte (LFA-1) and adhesion molecules on endothelium (ICAM-1) combine to halt rolling adhesion (A strong interaction is induced by CXCL8 held on proteoglycans of extracellular matrix and cell surface to form a gradient for leukocyte to travel)
Under guidance of chemokines, neutrophils squeeze between endothelial cells and penetrate connective tissue
Leukocyte migrates to center of infection along CXCL8 gradient.
What type of protein is ICAM?
Immunoglobulin-like molecule
What type of protein is LFA-1?
Integrin
What is another name for extravasation?
Diapedesis
What is the principal means by which immune system destroys invading pathogens?
Phagocytosis of microbes by phagocytic cells.
What do macrophages do?
They are long lived, reside in tissues, work from very beginning of infection doing multiple functions
What do neutrophils do?
Short-lived, dedicated killers, circulate in blood until they get stimulated by macrophages to enter tissue that is infected.
How long are mature neutrophils kept in bone marrow for before being released into circulation?
5 days
How many neutrophils enter tissues of mouth and throat daily?
3 billion
What kind of conditions are neutrophils made to work in?
Anaerobic conditions and die after phagocytosis (within hours of entry to inflamed site)
What is produced when there is a huge amount of neutrophil death?
Pus is formed
How are neutrophils different to macrophages?
They have a wider range of phagocytic receptors and complement receptors.
They can engulf a greater range of particulate matter than macrophages and have greater diversity.
They have a greater diversity of microbicidal substances in granules.
What kind of microbicidal substances are found in neutrophil granules?
Primary granules (contain myeloperoxidase)
Secondary granules (lactoferrin)
Tertiary granules (gelatinase)
What do neutrophils do to kill bacteria after phagocytosis?
Granules full of lytic enzymes and substances as well as lysosome fuse with phagosome and thus bacteria is degraded.
Neutrophil then undergo apoptosis and are phagocytosed by a macrophage.
Dying neutrophils also produce extracellular traps (NETs)
What do dying neutrophils produce?
Neutrophil extracellular traps (NETs)
What is a NET?
A mesh matrix which can stick other creatures in this site holding them in place.
What can macrophages do to the liver?
They produce IL-1/IL-6/TNF-alpha which act on the liver to produce acute-phase proteins which activate complement opsonisation
What can macrophages do to the bone marrow endothelium?
Produce IL-1/IL-6/TNF-alpha which produce more neutrophils and increase phagocytosis
What can macrophages do to the hypothalamous and muscle/fat?
They produce IL-1/IL-6/TNF-alpha which:
Increase body temperature
Protein and energy mobilization to generate increased body temperature
Resulting in a decreased viral and bacterial replication rate
What are cytokines and other molecules that induce a fever called?
Pyrogens
Where are pyrogens produced?
Exogenous (bacteria can produce them)
Endogenous (body can produce them)
What does the hypothalamus do in response to pyrogens?
they release prostaglandins which raises hypothalamic thermostat to a higher temperature
What are acute-phase protein functions?
Innate response occuring soon after start of infection
Which acute phase proteins are involved in pathogen recognition?
C-reactive protein
Mannose-binding lectin
LPS-binding protein
Which acute phase proteins are involved in pathogen elimination?
Complement components
Which acute phase proteins are involved in the inflammatory response?
Granulocyte colony stimulating factor, serum amyloid A, secreted phospholipase A2
What are acute phase proteins?
Diverse plasma proteins made rapidly in large amounts
What happens to C-reactive protein levels and serum amyloid A after inflammatory stimulus?
They jump up in concentration immediately
What happens to fibrinogen following inflammation?
Fibrinogen comes in slightly later (after several days)
Which proteins are elevated post-inflammation/
C-reactive protein and serum amyloid increase immediately to huge levels.
C3 and fibrinogen are moderately elevated
Serum albumin drops during acute phase
What does C-reactive protein look like?
It is a pentraxin (5 subunit family).
Polypeptide backbones of 5 subunits are traced by ribbons of different colour.
CRP resembles a pentagonal slab with hole in the middle.
