IMI 4: Inflammation and Autoimmune Inflammation Flashcards
1
Q
Observe the learning outcomes of this session
A
2
Q
What is the simple definition of inflammation?
A
- inflammation is a common immune response to all sorts of damage and insult that your body suffers and its purpose is to limit an infection to an area and stop it from spreading, or to remove damaged cells and dead tissue, and to expedite the speed with which immune cells can come to the affected site and start fixing ‘things’
3
Q
Apart from the simple definition of inflammation, what else can it be?
A
- a response:
- to an infection or injury
- a process:
- multi-step signalling cascade leading to the production of cytokines and initiation of additional immune effetor functions
- a state of system:
- which can protect or attack the body
4
Q
What is acute inflammation and what are clear signs of it?
A
- accumulation of the following at the site of injury or infection:
- leukocytes: mainly neutrophils and with time circulating macrophages
- plasma proteins
- fluid derived from blood
- Complement proteins, antibodies and acute phase response proteins also enter the inflammatory site thanks to an increased blood flow and increased permeability of capillaries and venues
5
Q
What causes acute inflammation?
A
- cytokines
- small molecule mediators initially produced in cells resident in the tissues under attack or damaged:
- tissue-resident macrophages
- mast cells
- DCs
- endothelial cells
- these are reversible changes and are the responses to the initial sensing of DAMPs and PAMPs
6
Q
Describe the stages of acute inflammation
A
- Tissue damage and bacteria cause resident sentinel cells to release chemoattractants and vasoactive factors that trigger a local increase in blood flow and capillary permeability
- Permeable capillaries allow an influx of fluid (exudate) and cells
- Neutrophils and other phagocytes migrate to the site of inflammation (chemotaxis)
- Phagocytes and antibacterial substances destroy bacteria
7
Q
Describe the inflammatory response after bacterial entry
A
- bacterial entry leads to the activation of the innate immune system, which includes phagocytosis by resident cells (eg macrophages, DCs) and activation of PRRs
- PRR signalling leads to the production of cytokines, chemokine and other mediators that trigger vascular changes responsible for the influx of a number of antimicrobial molecules and phagocytes (first neutrophils, then monocyes)
8
Q
What processes follow the inflammatory response?
A
- redness: due to higher blood volume
- swelling: due to increased vascular permeability, which leads to leakage of fluid from blood and an accumulation of fluid (oedema);
- heat: due to higher blood flow
- pain: due to e.g. swelling leads to compression of nerve endings;
- loss of function
9
Q
Observe this list of the many inflammatory cytokines, their sizes, sources and effects
A
10
Q
What are the key characteristics of cytokines?
A
- produced mainly by macrophages and DCs:
- mast cells, endothelial cells and some epithelial cells can also produce them
- act mainly in a paracrine fashion
- can also act in an endocrine fashion
- some redundancy as different cytokines can have similar or overlapping biological functions
- some cytokines also have unique functions
- can stimulate the transcription and activation of others
- triggering a cascade of events that either amplify the initial response or initiate other responses
- are pleiotropic:
- they have several different roles
- these can include inflammation, antiviral responses (which lead to inhibition of viral responses), promoting T cell responses and downregulating innate immune responses;
- can be produced during innate responses but, the same cytokine, can also play roles in adaptive responses.
11
Q
What are the three major pro-inflammatory cytokines?
A
- TNF
- IL-1
- IL-6
12
Q
Briefly explain what tumour necrosis factor (TNF) does
A
- tumour necrosis factor (TNF) was first identified as a factor that caused necrosis of tumours, something that can be attributed to its ability to induce inflammation and thrombosis of blood vessels.
- It is a well known mediator of inflammation in response to bacteria and other infectious pathogens.
- Its biological functions are mediated by its binding to TNF receptors and subsequent signalling that culminates in NF-kB and AP-1 activation and transcription of key target genes.
- TNF signalling can also under some circumstances lead to the activation of caspases and apoptosis
13
Q
Briefly explain what interleukin-1 (IL-1) does
A
- Interleukin-1 (IL-1) is also a mediator of inflammation and shares some of TNF’s functions.
- There are two forms and IL-1β is the main biologically active form and the one we have been discussing thus far.
- Interestingly, the activation of IL-1β requires two signals: a transcriptional one (via TLR and NLR signalling down to NF-kB) that leads to the production of the 33 kDa precursor pro-IL-1and another one that activates the inflammasome and proteolytically cleaves pro-IL-1β into the active 17 kDa polypeptide, the mature form of IL-1β.
- TNF can also stimulate some cell types to transcribe IL-1β.
- Interestingly, IL-1 is secreted by a non-canonical pathway and does not involve the endoplasmic reticulum (ER);
- instead, it seems that it is secreted via pores in the membrane caused by gasdermin D oligomerisation, which we mentioned when we discussed pyroptosis.
- Like TLRs, the IL-1R possesses TIR domains and signals down to NF-kB and AP-1.
14
Q
Briefly explain what interleukin-6 (IL-6) does
A
- Interleukin-6 (IL-6) can act locally and systemically, inducing the synthesis of acute phase proteins (e.g. CRP, SAP and fibrinogen) in the liver, neutrophil production in the bone marrow and differentiation of IL-17-producing helper T cells.
- It is produced in responses to PAMPs, IL-1 and TNF. IL-6 signals through Janus kinases (JAKs) down to Signal Transducers and Activators of Transcription (STATs), particularly STAT3.
- It is thought to be one of the main culprits involved in chronic inflammation seen in pathologies such as rheumatoid arthritis (RA) and anti-IL-6 antibodies have been game changers in the treatment of these diseases.
15
Q
Summarise the key roles of TNF, IL-1 and IL-6 in inflammation
- local inflammation
- systemic protective effects
- systemic pathologic effects
A
- The image summarises key roles of TNF, IL-1 and IL-6, which can be local or systemic.
- TNF and IL-1 can act on leukocytes and endothelial cells causing inflammation and lead to the transcription IL-6 from leukocytes and other cell types.
- All three cytokines paradoxically have protective effects too by inducing fever (TNF and IL-1 act on the hypothalamus and increase body temperature), triggering the production of acute phase proteins in the liver and the production of more leukocytes in the bone marrow.
16
Q
What is fever?
Which organisms does it affect?
A
- Fever is the systemic rise in temperature.
- What is perhaps most surprising is that fever is an evolutionarily ancient process: cold blooded animals (fish and lizards) engage in heat-seeking or heat generating activities when infected, and even plants can boost metabolism – and thus temperature – in response to infection .
- In mammals, temperature might be boosted by up to 4 degrees, mediated centrally by the brain (via the hypothalamus) in response to inflammatory cytokines.
- In mice, IL-6 has been shown to be particularly important, but it is not known whether different cytokines are important for driving fever in different contexts.
- This temperature rise is based on a huge increase in cell metabolism, so the body has a higher demand for energy.
17
Q
What does increasing in temperature from fever do to immune cells?
A
- In cells, elevated temperature has been shown to reduce the efficiency with which certain viruses replicate, although it is not clear whether this interferes with virus or cell functions.
- elevated temperature enhance immune cell migration, increasing binding strengths of selectins and some integrins to their ligands; and increasing levels of these or their ligands on immune vascular cell surfaces.
- These effects combine to generally enhance the ability of immune cells to roll to a stop on vessel walls, and then migrate into tissues.
- This effect is seen in particular for T cells, whose levels in the blood fall and in tissues increase.
- Neutrophil levels in circulation increase, and migrate into the lung, although this can have an undesirable effect in disrupting the lung’s barrier function.
- Heat can also prompt professional APCs to migrate to lymph nodes, and more broadly increases the number of all sorts of immune cells that migrate through lymph nodes.
- Dendritic cells are particularly responsive to heat: they increase the levels of MHC molecules and co-stimulatory ligands on their surface, allowing them to activate T cells more easily, while the increased temperature also boosts the proliferation of T cells.
18
Q
Why do we take drugs to reduce fever if fever reduces efficiency of viral replication?
A
- In cells, elevated temperature has been shown to reduce the efficiency with which certain viruses replicate, although it is not clear whether this interferes with virus or cell functions.
- Conversely, taking drugs to reduce fever can increase the risk of death from virus infections like flu.
- These drugs (e.g., aspirin, ibuprofen), however, also interfere with other innate immune processes, and it is not completely clear which is more important: blocking fever, or other immune functions?
19
Q
Why do we feel cold when we have a fever?
A
- our body increases the temperature to fight, for example, an infection.
- As soon as this happens and this sets your ‘thermostat’ to >37 ˚C.
- So the body starts trying to generate extra heat but as soon as this is the case, your body senses that you are below your new optimal temperature.
- Because you now feel cold, you start shivering to generate extra heat by contracting your muscles.
20
Q
What are IL-1β and IL-18?
How do they get into action really quickly?
A
- they are key pro-inflammatory cytokines, activated when cells mount an antiviral or inflammatory response
- These are powerful molecules that our bodies must not deploy unless there is a very good reason to do so.
- But once they do, these cytokines get into action as fast as possible.
- This is only possible because they exist as inactive precursors, which are readily activated by a quick process of proteolytic cleavage by a protein called caspase-1.
21
Q
What activates caspase-1?
A
- caspase-1 activation is very tightly regulated
- it is the result of the formation of the inflammasome
- which are formed in the cytosol after PAMPs and DAMPs are recognsied, or changes that are the result of infection or damage are detected
22
Q
What does the inflammasome complex consist of?
A
- they contain a triad of proteins:
- oligomers of a sensor
- caspase-1
- an adaptor that links the sensor to caspase molecules
23
Q
What do protein-protein interactions require?
A
- matching domains on each protein
- these homotypic interactions happen because these proteins share structural domains.
24
Q
Observe the figure to see the shapes of different inflammsome triads
A
- Inflammasomes exist in many shapes: this triad is maintained but the precise composition can vary.
- For example, members of the NLR (NOD-like receptor) family such as NLRB, NLRC4 and several NLRP proteins, and other cytosolic sensors such as AIM2 and IFI16, share a DNA sensing domain and a pyrin domain (PYD), form different inflammasomes.
25
Q
Observe these diagrams of inflammasomes
A
27
Q
Observe this figure of the different types of molecules that can trigger the inflammasome
A
28
Q
Describe how the inflammasome is formed
A
- the ligand (eg. bacteria, ATP) binds to the receptor (a sensor such as NLRP3), and then multiple receptor molecules interact to form an oligomer.
- If we take NLRP3 as an example, in it each NLRP3 sensor molecule will bind to an adaptor such as ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain, or CARD).
- This leads to a conformational change in the receptor triggering changes in ASC that resemble a chain-reaction, or a series of dominos knocking each other down.
- The resulting ASC filaments cluster and, in the process, recruit inactive precursor molecules of caspase-1 (pro-caspase-1).
29
Q
How is active caspase-1 generated?
What is its function?
A
- Clustering of pro-caspase-1 leads to the generation of active caspase-1.
- Although, most of the other caspases are involved in cell death processes, particularly apoptosis, the main function of caspase-1 is the activation of IL-1β or IL-18.
- Once active, these cytokines can be secreted and induce inflammatory signalling in neighbouring cells, leading to the elimination of the pathogen or damage that triggered the activation of the inflammasome in the first place.
31
Q
What are the mechanisms resulting in NLRP3 activation?
A
- Transcription of IL‐1β and NLRP3 can be induced by TLR signalling.
- At the same time, NLRP3 can be primed by a TLR‐dependent, but transcription‐independent signalling event.
- Various stimuli can activate NLRP3 which is believed to be expressed in an auto‐inhibited state.
- Activated NLRP3 presumably forms multiprotein aggregates with the adaptor protein ASC and recruits caspase‐1.
- Autocatalytically activated caspase‐1 in turn processes pro‐IL‐1β to an active and secretable form.
- A plausible common downstream mechanism, or signalling mediator that integrates the various processes induced by a plethora of canonical NLRP3 stimuli, has not been identified but various models including as ROS production or Ca2+ release from the endoplasmatic reticulum (ER) were proposed.
- In contrast to these stimuli, non‐canonical stimuli such as live gram‐negative bacteria additionally require caspase‐11 for full caspase‐1 activation.
- The activity of caspase‐11 is transcriptionally regulated by type I IFN signalling that is simultaneously engaged by bacterial compounds via TLR activation.
- The molecular mechanisms linking caspase‐11 to caspase‐1 have not been entirely identified.
36
Q
Compare the pathways between non-inflammatory apoptosis and inflammatory pyroptosis
A
38
Q
Can you match the proteins on the right with the type of protein on the left?
A
40
Q
Which transcription factors are involved in inflammatory responses?
A
- NK-kB
- STAT3
- AP-1
43
Q
What are autoinflammatory diseases?
What is another name for them?
A
- Autoinflammatory diseases are a group of rare diseases characterised by seemingly unprovoked episodes of fever and inflammation.
- Because the inflammatory episodes occur regularly, the diseases are also known as periodic fever syndromes
- they involve abnormal activation of the innate immune system.
- In autoinflammatory diseases, however, the innate immune system is activated without an apparent cause and it remains activated for some time - there is no down-regulation.
49
Q
How has MEFV mutation led to an evolutionary advantage?
A
- FMF carriers may have had an evolutionary advantage in the past, such as possibly a diminished vulnerability to infections prevalent in their environment.
- These ancient MEFV mutations appear to have originated in the Middle East in Biblical times.
- In fact, there have been descriptions of periodic fevers since antiquity.
- For example, Galen, a doctor in ancient Rome (129 AD – c. 200/c. 216), described cyclic fevers that he attributed to the different moon phases, as early as during the second century AD.
- The mutations in MEFV have been mapped to understand the spread of autoinflammatory diseases, as shown in the map.
- One mutation migrated to Spain and north-Africa, either via early sailors from the Middle East or eastward via land migration later during the Muslim conquests of Spain.
- Another mutation also migrated from the Middle East to Armenia, Turkey, and Europe in migrating Jewish populations.
50
Q
What is the treatment for autoinflammatory diseases?
A
- colchicine:
- The long-term treatment of many autoinflammatory diseases is with low doses of colchicine, a compound originally extracted from plants of the genus Colchicum
- Continuous treatment with colchicine prevents, or substantially reduces, symptoms of FMF in at least 95% of the patients.
- Although how colchicine works is not completely understood, it is thought to inhibit multiple proinflammatory mechanisms and thereby relieve symptoms.
- IL-1β inhibitors:
- Given that IL-1β is often overexpressed in autoinflammatory diseases, it is hardly a surprise that newer therapeutical approaches tend to target IL-1β.
- Medicines such as anakinra, rilonacept (also known as IL-1 Trap) and canakinumab, which target IL-1β or IL-1β receptor binding, have in recent years revolutionised the management and treatment of autoinflammatory diseases.
55
Q
Explain central tolerance
A
- Central tolerance occurs in the organ of maturation for the respective lymphocyte.,
- i.e. thymus for T-cells and bone marrow for B-cells.
- Central tolerance is the combination of mechanisms that make sure new developing lymphocytes avoid reacting to self-antigens: newly developing T-cells and B-cells that do react to self-antigens undergo modulation of their antigen receptors, become functionally inactive (anergic) or are deleted by apoptosis.
56
Q
Explain peripheral tolerance
A
- Peripheral tolerance occurs outside the organ of maturation, but at the site of antigen recognition, where lymphocytes could begin to elicit an immune response.
- This can occur in the circulation, lymph nodes, lymph organs, or other tissues.
- Peripheral tolerance is the mechanisms that prevent lymphocytes from initiating immune responses against our own tissues, or against harmless material, like commensal organisms or food.
59
Q
What will stop a T cell from helping a B cell to attack a harmless environmental antigen?
A
61
Q
How do Treg maintain tolerance?
A
- Evasion:
a) sequestration/partitioning of antigens
b) Immuneprivileged sites, e.g. eye
c) These antigens rarely become part of peripheral tolerance pathways
- Elimination:
a) negative selection of high affinity self-reactive lymphocytes
- potentially the most dangerous
b) receptor editing
- VJ recombination (light chain loci)
- results in less autoreactive receptors - Engagement
a) Development of Tregs
