Advanced Immunology Flashcards
What is the GALT
Gut-associated lymphoid tissue, produces majority of Ig
What is the gut the site of?
Peripheral tolerance
What is Peyers patch differentiation driven by?
Lymphoid Tissue inducer
What does Lymphoid tissue inducer cause?
Induction of TNF-family cytokine expression.
How does antigen capture occur in the Gut Mucosa?
- Transcytosis via the Peyer’s Patch (M-cells)
- FcRN-dependent transport, neonatal Fc receptor.
- Enterocyte-injected with intracellular pathogen = entry via apoptsis, due to phagocytosis mediated by DCs.
- Macrophages
- Uptake via Goblet Cells
- Capture via Intraepitheial Cells
What drain to lymphocytes and educate naive T cells about food-derived antigens?
CD103+ Dendritic cells.
What do CD103+ Dcs do?
Secrete TGF-beta to generate iTregs.
What do Macrophages secrete to avoid inflammation induction?
IL-10
What does IL-10 do?
Aid survival and expansion of iTreg cell primed by Tolerogenic DCs.
What do gut epithelial cells secrete to induce tolerogenic properties of gut CD103+ Dcs?
Retinoic acid, TGF beta and thymic stromal lymphopoeitin
What directly exposes M cells to microorganisms?
The lack of mucus/glycoalyx
What are M-cells specialized for?
Passing antigens from the gut to Dendritic cells.
How does antigen uptake occur using M cells?
Endocytosis and Transcytosis
Which pathogens are known to exploit M cell entry route?
Salmonella Enterica, Typhi, Shigella, Yersinia Pestis, HIV and Scrapie prions
What do gut homing T and B cells express?
Integrin alpha4beta7, which binds MAdCAM-1
What does MAdCAM1 stand for?
Mucosal Vascular Addressin Cell adhesion molecule-1.
Where is MAdCAM-1 expressed?
Mucosal Tissue
What do lymphocytes destined for the epithelium in small intestine express?
CCR9, which allow CCL25 mediated recruitment
What do lymphocytes destined for the epithelium in large intestine express?
CCR10, allows CCL28 mediated recruitment
What do intraepithelial Lymphocytes express?
They lose Alpha4Beta7 and express integrin AlphaEBeta7 which binds E-cadherin.
Where do CD4 IELs remain?
In the lamina propria
What is the role of IgA?
It helps to maintain homeostasis between host and commensal bacteria
How does IgA prevent microbial adherence?
By binding and neutralising toxins.
How does IgA protect against viruses and bacteria?
By neutralising endocytosed viruses and bacterial lipopolysaccharides.
What effect does IgA have on M cells?
It enhances antigen uptake and restricts entry o fbacteria
How does IgA lead to enhanced iTreg expansion?
Dendritic cells uptake IgA-antigen complexes through binding to DC-SIGN.
This generates tolerogenic SIgA-DCs which become resistant to TLR-stimulated maturation and secrete IL-10.
This leads to enhanced iTreg expansion
How does IgA reduce Inflammation?
It does not activate complement
How does transport of IgA to the lumen occur?
Through endocytosis and trancytosis.
What does DC-SIGN mean?
Dendritic cell specific ICAM-3 grabbing non-integrin
What does SIgA-DCs mean?
Secreted IgA-primed DCs
Where are B cells primed?
Peyers patch and mesenteric Lymph node
Which interleukins are involved in expansion admn differentiation post B cell switching?
IL-6 and IL-10
What percentage of IELS are CD8+?
80%
What are the types of IEL cells?
Type A and B
What do Type A IELs do?
Express CD8 alphabeta and TCR alphabeta.
Primed and home to mucosal epithelium.
What do Type B IELs do?
Express alphabeta or gammasigma TCR but always express CD8 alphaalpha.
Can help repair of damaged epithelium.
Kept in check by co-expression of inhibitory receptors and TGFB expression
What is celiac disease an example of?
Dysregulated IEL activity due to increased gammasigma TCR IELs. Lead to abnormal responses to alpha-gliadin of gluten which leads to IL-15 secretioon and Mic-A expression.
Type B IELs are activated and kill epithelial cells.
How does the gut innately sense infection?
Via TLR and NOD
What is an example of a pathogen that activates NOD?
Staph Aureus
What expresses NOD1 and NOD2?
Epithelial cells, macrophages and DCs.
What does NOD1 sense?
Gamma-glutamyl diaminopimelic acid - breakdown product of peptidoglycans from gram negative bacteria (salmonella) and gram positive (listeria)
What does NOD2 sense?
Senses muramyl dipeptides found in the peptidoglycans of most bacteria.
What do mutations of NOD2 show?
Impaired NFkB-driven defensin expression associated with Crohns.
What other bacterial products does NOD sense in the cytosol?
LRR - leucine rich repeats
CARD - Caspase recruitment domain
TAK-1 - TGF beta activated kinase 1
How do bacterial ligands lead to NFkB activation through NOD?
They bind to NOD which leads to RIP2 recruitment, activating TAK1 and NFkB.
What is the inflammasome comprised of?
NLRP3, ASC and Caspase1
What do Paneth cells secrete?
Anti-microbial proteins Defensins and Reg3y.
What are defects in Paneth cells attributed to?
Inflammatory bowel disease.
What do bacteria do for us?
- Metabolism of dietary constituents (e.g Cellulose)
- Degradation of Toxins
- Generation of essential cofactors
- Generation of beneficial metabolites
- Protection from pathogenic infections
- Normal immune system development
What is CAR-T?
Chimeric Antigen Receptor Therapy
What does CAR-T do?
Combine antibody with a T-cell receptor
How does CAR-T therapy work?
Take blood, extract T cells then engineer to express Chimeric receptor and multiplied up and injected back into the patient.
How do Chimeric Antigen receptors cause cytotoxic destruction of tumour cells?
Artificial ligand binding domain of the receptor engages with the antigen.
Causes conformational change which leads to signal domain activation.
T cell becomes activated in response, leading to destruction.
How do costimulatory domains of Chimeric Antigen receptors affect their function?
If you add additional units, they cause more potent T cell activation
What are CAR-T cells currently used to treat?
B cell Lymphomas and Leukeamias
What are leukemias?
Haematological cancers
What does CAR-T therapy target in Lymphomas?
CD19 antigen on the tumors. Antibody modified to target this.
What other potential CAR-T uses have been tested?
Lupus caused by excessive B cell activity. Could use CD19 to deplete B cell stores in mice.
How can CAR-T therapy be improved?
Figuring out mechanisms to switch off normal B cell responses
What experiments have been conducted in mice to switch of CAR-T cell activation?
T cells were engineered to express CAR and truncated human epidermal growth factor.
When they wanted to switch off CAR-T responses, they added an antibody targeted at the truncated receptor (Cetuximab).
This led to antibody-induced cytotoxic responses, destroying CAR-T cells.
What are disadvantages to CAR-T?
Cost, difficulty in harvesting enough cells. Removal of endogenous TCR and deletion of MHC genes in order for host to accept the therapy.
How are Cancer vaccines produced?
- Patient Dendritic cells are taken.
- Injected with DNA encoding PSA (prostate specific antigen) and GMB-CSF (CSF promotes DC expansion)
- DCs then present PSA to T cells when injected back into the patient
What are prophylactic vaccines?
Preventative, e.g HPV
What are Therapeutic vaccines?
Designed to fight existing infections/ administered after onset.
How are neoepitope vaccines produced?
- Exome sequencing of tumour biopsies.
- Neoantigen prediction
- MHC Class II antigens are particularly important.
- Vaccine generation
What type of neoepitope vaccines have been used in phase 1 clinical trials?
mRNA, peptide and dendritic cell vaccines
What does CAR-T cell therapy rely on?
Cell surface tumour associated antigens (taa) and tumour specific antigens (tsa)
What is the 3rd signal required for T cell activation?
CTLA-4
How has CTLA-4 been targeted to improve immune responses to cancer?
T cell responses can be potentiated by disrupting CTLA4-CD80/86 interaction.
Monoclonal antibodies can be made which bind to CTLA4, freeing up CD80/86 to bind to CD28 allowing reactivation of the T cell.
Which drug targets CTLA4?
Ipilimumab
What is the role of CTLA-4?
Binds to CD80/86 as it has a higher affinity than CD28 does.
Sends inhibitory signals to the T cell, dampening the response and inactivating the cell.
How else are T cell responses potentiated?
Through modification of PD1-PDL1 interactions.
What happens when PD1 and PDL1/2 interact?
An inhibitory signal is sent to the T cell which dampens T cell responses/
What PD1/PDL1 interaction an example of?
The tumour working to suppress immune responses
How can PD1/PDL1 interaction be prevented?
By targeting antibodies to PD1/PDL1/2 to stop the interaction and allow reactivation of the T cell.
What is the clinical importance of immune checkpoint inhibitors?
They have had strong impacts on previously difficult to treat cancers.
Ipilimumab - Improved long-term survival.
What advantages are there to PD1/PDL1/2 targeted treatments?
They have seen to have a broader spectrum than CTLA4 inhibitors.
When have increasing drug response rates to cancer been seen?
With combination therapy
Problems with specific antibody therapies and cancer?
Therapeutic antibodies are expensive and possess significant acute and long term toxicities (Ipilimumab)>
What types of cancers respond well to immune checkpoint inhibition?
Those with many mutations, as it means there are more immune cells present in the tumours
What does it mean when cancers have a high tumour mutational burden?
They are considered TMB high and are more likely to respond to tumor immune checkpoint blockade.
When are tumors reported as immune hot?
When there are lots of CD8+ T cells.
What is a good way of predicting how tumours will respond to tumour immune checkpoint blockade?
By determining whether tumours were hot or cold
What makes it more likely for patients to respond to tumour immune checkpoint inhibitors?
More mutations and more CD8 T cells
How are tumors determined to have necessary checkpoints?
You can stain for PDL1
How does resistance to PD1 blockades arise?
Mutations in oncogenes. Tumour selects for genes that confer resistance to T-cell mediated killing.
Who came up with the cancer immunity cycle?
Chen and Mellman
What is tumour immunology characterized by?
The cancer immunity cycle
What is the cancer immunity cycle?
- Cancer cells die and release antigens and interferon 1
- Cancer antigens are then presented on APCs.
- APCs migrate to the Lymph nodes and present to Naive T cells
- Naive T cells traffick back to the tumor.
- T cells infiltrate the tumour
- T cells recognise the cancer cells
- Mediate cell destruction of cancerous cells
What activates Antigen-presenting cells to migrate to the lymph nodes once loaded with cancer antigen?
Interferon-1
How do Tumors evolve?
Through immune suppression or immune exclusion
What do cells with green nucleus represent in staining?
FOXP3 presence, regulates T cells
How can tumors use T cells?
They can hijack regulatory T cells to suppress their cytotoxicity.
What does the immune exclusion theory of Cancer development suggest?
Cancer cells are able to proliferate as they do not let in any immune cells.
How do tumors evade immune recognition through low immunogenicity?
- Presenting less antigen = reducing the likelihood of recognition.
Downregulates peptide-MHC ligands/MHC, no adhesion molecules, no costimulatory molecules.
How do tumors evade immune recognition through being treated as self antigen?
Tumor antigens can be taken up and presented to APCs without costimulatory molecules which leads to tolerisation of T cells.
How do tumors evade immune recognition through antigenic modulation?
Antibodies produced against tumor cell-surface antigens can cause endocytosis and degradation of the antigen. This leads to immune selection of antigen-loss variants.
How do tumors evade immune recognition through immune suppression?
TGF-B, IL-10 and iDO secreted by tumor cells inhibit T cells directly. Induction of regulatory T cells by tumors.
How do tumor-induced privileged sites lead to immune evasion?
Factors secreted by tumour cells create physical barriers to the immune syste,
What do Tumor cells secrete to evade the immune system?
- Collagen via cancer associated fibroblasts
If tumor infiltrating lymphocyte levels are ___, prognosis was ___
high, better
If smooth muscle actin levels are ___, prognosis was ___
low, better
What proved the roles of SMA and Tumor infiltrating lymphocytes?
Blocking myofibroblast differetiation permitted T cell infiltration in mouse tumor models.
How do cancers change their metabolism?
They start to produce their ATP through the Warburg effect.
What does the Warburg effect mean?
Cells consuming a huge amount of glucose
Why would tumor cells preferentially alter their metabolism to the Warburg effect?
High glycolytic activity leads to a buildup of lactate, which is an immune suppressant.
Can downregulate immunostimulatory molecules
What can lactate downregulate?
Important chemokines such as CXCL10- important for T cell trafficking to the tumor
What do tumors selectively lose to aid survival?
Immunogenic neoantigens
What stage of the cancer immunity cycle would loss of antigen presentation affect?
Migrated T cells recognising tumour antigens would be affected with reduced presentation.
How do cancer cells mediate reduced antigen presentation?
MHC downregulation, prevents CD8+ recognition
What makes T cells migrated from the lymph nodes more likely to kill tumors?
High MHC presence
What backups does the immune system have if tumor cells switch off MHC?
Natural killer cells and macrophages
How do Natural Killer cells mediate destruction of tumors with low MHC1?
NK are switched off with normal MHC1 levels but attack cells with lower MHC 1 or altered MHC
How do Macrophages mediate destruction of tumors with low MHC1?
They are capable of antibody-dependent cellular cytotoxicity and secrete anti-tumor factors.
How are mice used to monitor NK cell activity against tumors?
Nude mice have higher levels of NK cells but lack T cells.
Tumors more susceptible to NK cells grow slower in nude mice than normal mice.
What does the activation of TCR signalling without co-stimulation of CD28 lead to?
T cell anergy
What does CTLA4 have a higher affinity than CD28 for?
CD80/86
What are immune checkpoints critical for?
Controlling the extent of immune responses
What does CTLA4 engagement mean?
T cell receptor signalling is inhibited
What does PD1 stand for?
Programmed death 1
What is the hallmark of cancer cells?
Avoiding immune destruction
How does cancer arise?
Stepwise accumulation of mutations
What are key prognostic factors in solid tumors?
Nature and extent of immune cell infiltrates
What increases the risk of developing tumors?
Immunosuppression in patients
What makes Tumor specific antigens unique?
Do not occur on normal body cells
How do Tumor specific antigens arise?
Through DNA mutations that lead to the expression of altered forms of self cellular proteins.
Or through the expression of viral antigens by virally infected transformed cells.
Are Tumor assoociated antigens specific to tumor cells?
No, found on normal body cells. Much more common than TSAs.
What are the six categories of tumor rejection antigens expressed?
-Somatic mutations (neoantigens)
- Antigens expressed in germ cells
- Tissue restricted antigens = upregulated
- Antigens upregulated due to abnormal gene regulation
- Antigens that exhibit abnormal post-translational modifications
- Antigens expressed as a result of oncogenic virus infection
What are cues that lead to detection of cancerous cells?
Faulty proteins, stress signals and innapropriate gene expression
What is tumor immunoediting?
An extension or refinement of the theory of tumor immunosurveillance, in which the immune system acts as a key selective pressure that shapes tumor evolution.
What is tumor immunosurveillance?
The idea that the immune system is constantly looking out for cancerous cells.
How are cancerous cells flagged during development?
- Elimination, cells dividing are flagged to the immune system due to antigens.
- Equilibrium, immune system controls growth but doesnt pick off every cancer cell. Leads to mutations.
3.Escape, cells have acquired mutations which allow them to evade the immune system
What is evidence for immunoediting?
- Immunocompetent mice, initiated tumor via carcinogenic paint.
- Waited for tumor growth, take cells from tumor and grow in dish.
- Inject back into mouse
- Tumors found in the mice.
EDITED PROGRESSORS
How did immunodeficient mice respond to cancer injection?
- Tumor grew, took cells.
- Injected, Some cells grew further
UNEDITED PROGRESSORS
What do mice injected with cancer cells support?
Idea of immunotherapies to kickstart the immune system.
Which elevated levels can be useful in the diagnosis of cancer?
- Onco-foetal antigens
CEA - carcinembrynic antigen
AFP - alpha foetoprotein
What cytokine is upregulated due to Co-stimulation?
IL-2
How does Costimulation lead to IL-2 increase?
CD28 signals via PI3K to activate AP-1 and NFkB Transcription factors.
IL-2 mRNA is unstable, CD28 induces factors to block degradation of the mRNA.
PI3K-Akt survival signalling promotes growth and survival. = IL-2 production
How many chains compose the IL-2 receptor?
3, gamma, beta and alpha
Which sections of the IL2 receptor do resting mature T cells express?
Beta and Gamma, with moderate affinity
What does expression of only 2 sections of IL2 receptor mean?
Resting T cells respond to only very high IL2 concentrations
What happens when IL2 activates T cells?
Alpha chain is produced = trimeric receptor.
Capable of responding to low IL-2 concentrations
Which cells express the intermediate affinity Beta and gamma chains?
Naive T cells and NK cells
What happens once IL-2 activates cells?
The cells can secrete IL-2 and divide up to 4 times a day
What do Tregs express in regard to IL-2?
the alpha chain (CD25) constitutively
What is a component of many vital cytokine receptors?
The gamma chain
What is the syndrome called when you are born without the ability to produce the gamma chain?
X-linked SCID
Why is the gamma chain so intrinsic to cytokine function?
Cytokines cannot bind to intracellular JAK 3 tyrosine kinase without it. No signal is produced.
Means no cytokine-mediated effects can occur.
§What can STATs and JAKs regulate?
Transcriptional programmes that drive differentiation of T cell subsets.
What viruses are able to evade cytokine-mediated immune mechanisms?
EBV, Myxoma, Variola, HSV, Measles, Adenovirus
How are cytokines involved in TSS?
Superantigens bind to the outside of T cell receptors, causing activation of T cells non-specifically.
Leads to huge cytokine storm of tNF-a and iL1B = septic shock
How are cytokines involved in Chagas disease?
T.cruzi parasite causes drastic reduction in IL2-R a subunit
SCID Definition
Severe combined Immunodeficiency diseases
Why are people with SCID so susceptible?
They form no cell-mediated responses, no T cell-dependent antibody responses to pathogens
How do cytokines mediate their effects?
They bind to cell surface receptors, which signal via JAKS and STATs
Which interferons are produced upon sensing viral nucleic acids?
IFN a and Beta
How is viral RNA detected and processed?
Toll-like receptors on APCs recognise viral RNA in endosomes and process it via the endosomic pathway
Which receptors specifically recognise viral RNA?
RIG-1 and MDA5
What does cGAS recognise?
Cytoplasmic DNA
Which TLRs binding cause IFN expression
3 and 7
What type of viral genome causes IFN-a and IFN-B production>
dsRNA and ssRNA through triggering TLR3 and TLR7
How does TLR-3 signalling occur?
Through TRIF which activates interferon regulatory factor IRF3.
How does TLR-7 signalling occur?
Through pathway dependent on MyD88 in plasmacytoid DCs.
What are activated as a result of TLR-3 and TLR-7 activation?
IRF3, IRF7 and NFkB
What is RIG-I?
Retinoic acid-inducible gene I (senses ssRNA)
What is MDA-5?
Melanoma differentiation associated 5 (sense dsRNA)
Aside from RIG-I and MDA-5, what other units are involved in recognising cytoplasmic viral RNA?
CARD - caspase recruitment domain
MAVs = Mitochondrial antiviral signalling protein
What is cGAMP?
cyclic GMP-AMP
What is cGAS?
cGAMP synthase
What is STING
Stimulator of interferon genes
What do IFNa and B bind to?
IFN-a receptor
What is IFNa receptor comprised of?
Two separate chains. R1 and R2
What does IFN binding activate?
JAK1 and TYK2 and the formation of ISGF3 a transcription factor (heterotrimer of STAT1, STAT2 and IRF9)
What does ISGF3 expression lead to?
Type 1 IFN dependent gene expression (Interferon stimulated genes( isg))
What do Interferon stimulated genes mediate?
Effective antiviral responses
What does IFN a and B production cause protein transcription of?
Protein kinase R, 2,5 oligo A synthetase, Mx proteins and APOBEC family cytosine deaminases.
Which viruses suppress IFNa and B production by affecting RIG-I action?
Toscana, Influenza A, Hepatitis C and HBV
Which viruses suppress IFN a and B production by affecting IRF7?
Enterovirus and Megalocytovirus
Which viruses suppress IFN a and B production by affecting IRF3?
Poliovirus, Hepatitis E
What causes redness, heat and swelling in the inflammatory response?
Vasodilation and increased vascular permeability
How do lymphocytes migrate from the blood to the lymph nodes?
Through specialised post capillary venules, high endothelial venules
What is MALT?
Mucosal Associated lymphoid tissue, found in the GI tract, nasopharynx, thyroid, breast, lung, salivary glands and eye
What must lymphocytes do before they can enter inflamed tissues or lymph organs?
Adhere and penetrate the layer of endothelial cells
What is the process of lymphocytes and neutrophils passing through the walls of BVs called?
Extravasation
What are essential for allowing cells to adhere to correct endothelium walls?
Cell Adhesion Molecules (CAM)
How does CAM expression vary?
Can be expressed constitutively, or in response to cytokines/chemokines
What are the four basic CAM families?
- Selectins
- Mucins
- Integrins
- Immunoglobulin like CAM
What else are CAMs used for aside from adhesion?
Recognition between immune system cells
What are selectins?
Family of membrane glycoproteins containing a lectin-like domain at one end that binds specific CHO groups on mucin-like CAMs.
Which selectin is found exclusively on leucocytes?
L-selectin
Where are E-selectin and P-selectin found?
On vascular endothelial cells during inflammation responses
What do L-selectins do?
Bind to Mucin-like CAMs (CD34), GlyCAM-1 and MadCAM-1 found on endothelial cells.
What are selectin-Mucin CAM interactions critical for?
The first stage of extravasation
What are P and E selectins also known as?
CD62P and CD62E
Which selectins are involved in leukocyte binding to BV endothelium?
P and E
What do selectins bind to during extravasation?
Mucin-like CAMs on the neutrophil
What are Mucin like CAMs?
Group of serine/threonine rich proteins that are heavily glycosylated with carbohydrate chains, which bind to Selectins
Examples of mucins?
CD34 and GlyCAM1
What are Integrins?
Group of heterodimeric proteins which consist of (CD11) alpha and (CD18) Beta, expressed on the surface of leukocytes.
Which autosomal recessive disorder is caused by integrin B chain defects?
Leukocyte Adhesion Deficiency
What is the binding of leukocytes triggered by?
Chemokines which activate integrin expression
Which integrins are involved in leukocytes binding?
LFA-1, CR3, CR4 and VLA-5
What does integrin LFA-1 bind to?
ICAMS
What are immunoglobulins?
Group of CAM proteins that contain variable numbers of immunoglobulin like domains
Where are immunoglobulin like CAMs expressed?
On vascular endothelial cells, they bind to integrins on the surface of leukocytes
Which I-CAMs are involved in leukocyte binding?
ICAM-1, ICAM-2, VCAM-1, PECAM
What are ICAM1 and ICAM2’s ligands?
LFA-1
What is the first stage of Extravasation?
Reversible binding of neutrophils to the vascular endothelium through P+E selectin to Mucin-like CAMs on the neutrophil
What causes the rolling phenotype of extravasation?
Interaction of P+E selectins to Mucin like CAMs not being strong enough to withstand the flow of blood. Leads to continual making and breaking of interactions
What does the rolling allow binding of?
Stronger interactions –> with integrins, ie CXCL8 binding to CXCL8R on the neutrophil
What is the second step of extravasation?
CXCL8 to CXCL8R activating LFA-1, which binds to ICAM-1 and stops the cell from rolling.
What is it called when the neutrophil migrates through the endothelium following CXCL8 gradients?
Diapedesis
What is the final stage of extravasation?
Interactions with PE-CAM which allow the cell to traffic through the endothelium by being physically pulled
What do Neutrophils produce to assist extravasation?
Metalloproteinases which cut through. the matrix of the basement membrane, they also regulate chemokines
What do neutrophils follow to reach infected regions of tissue?
IL-8
What are High endothelial venules composed of?
Specialised cells with a plump cuboidal shape
What is important for the continued maintenance of efficient lymphocyte migration?
Foreign antigen exposure.
What allow homing of naive T lymphocytes to the spleen, lymph nodes or mucosal endothelium?
Mucin Like Addressins
Which selectins are expressed on naive t cells for homing to lymph tissues?
L-selectin
How to naive T cells use L-selectin to home ?
It recognises carbohydrate structures on Mucin-Like CAM molecules on the endothelium.
What do HEVs possess that direct extravasation of different populations of lymphocytes?
Vascular Addressins
Where do Effector lymphocytes home to?
Inflamed vascular endothelium
What does the signalling pathway stimulated by chemokines cause changes to?
The cytoskeleton and stickiness that allows migrate in BVs
What are inflammatory chemokines usually produced in response to?
Infection or other pro-inflammatory cytokines like TNF-a
What do Chemokines signal through?
G proteins
What does the binding of chemokines to receptors induce?
Signal transduction pathways
What do CC chemokines possess?
2 Cysteine residues, that bind to CCR G protein coupled receptors 1-9
What do CXC chemokines possess?
Same cysteines, but separated by other amino acid X. Bind to CXR G protein-coupled receptors
What are chemokines used for?
To attract particular cells to particular tissues
Where are the greatest variety of chemokine receptors found?
Activated T lymphocytes as they migrate everywhere
What cells are the first to arrive to infected tissue
Neutrophils
What are Neutrophils exposed to at the site of infected tissue?
CXCL8 chemokine, which they bind to via CXCL8R causing respiratory burst
What does a respiratory burst produce?
Oxygen radicals and release of cytoplasmic granules which kill bacteria in infected tissue
What arrive to infected tissues after Neutrophils?
Monocytes and Dendritic cells
What do mature APCs do?
Present antigen to naive T helper cells
What does APC antigen presentation to T cells lead to?
T lymphocytes expressing chemokine receptors
What chemokines do APCs produce?
IL-1B, TNF-a, IL-6, CXCL8 and iL12
What does membrane phospholipid breakdown in leukocytes cause?
Inflammation and more leukocyte migration
What are some diseases associated with HEV vasculature?
Diabetes Mellitus, Crohns, Graves, Hashimotos, Rheumatoid Arthritis, Ulcerative colitis.
What therapy has been introduced for IBD?
Anti-integrin, blocking integrin = inhibiting interaction of integrin and leukocytes/BV
How many types of hypersensitivity are there?
4
Which FCIgER is high affinity?
FCRIgERI
Which FCIgER is low affinity?
FCRIgERII
Where does the IgE bind to Fc receptors?
Its extra domain
What happens when allergen antigens bind to basophils or mast cells?
Further production of IgE antibody by B cells
How does IgE bind to basophils?
Via High affinity Fc receptors
What do basophils produce to stimulate B cell class switching?
IL-4
How do allergens prompt antigen-specific IgE production?
- Allergen antigen binds to basophils/mast cells via FcRIgERI
- Triggers release of IL-4
- This binds to IL-4 receptors, causing CD40 expression.
- Leads to B cell class switching to produce more IgE
What does signal transduction cause following IgE/allergen cross-linking?
- Degranulation
- Cytokines
- Leukotrienes and Prostaglandins
How do allergens prompt signalling cascades after secondary exposure?
- Alpha chains on mast cells and basophils bind IgE (B and y induce signal transduction)
- Leads to activation of tyrosine kinase which activates Protein kinase C and MAPK
- Transcription factors activate and cytokines are produced
What is the hallmark of inflammation?
Cytokine release
What does Leuktriene and Prostaglandin release cause?
Vasodilation, increased vascular permeability and other pro-inflammatory effects.
How do allergens cause degranulation of mast cells?
- Binding of allergen to IgE causes phosphorylation of Fyn and Lyn. Causes recruitment of Syk
- Syk phosphorylates LAT, recruiting signalling components leading to the activation of Phospholipase C-y (PLC-y)
- PLC-y cleaves PIP2, generating IP3.
- IP3 acts on ER receptors and causes Ca2+ release
- Ca2+ increases induce secretory vesicle membrane fusion to the plasma membrane, causes release of cytokines
What is PIP2?
Phosphatidylinositol 4,5 - bisphosphate
What is IP3?
Inositol 1,4,5-trisphosphate
How do food antigens induce tolerance in non-allergenic individuals?
Through Treg cell production, not TH2
How do food antigens cause responses in allergenic individuals?
Antigens induce Th2 production which leads to IgE producing B cells.
What seem to prevent food sensitisation?
Mucosal Associated commensal anaerobic bacteria
What cytokine limits access of food allergens to the blood?
IL-22 dependent response
Which T cells maintain responsiveness to ingested foods?
Foxp3+ Tregs
How do TLRs regulate food tolerance?
Bind to PAMPS to regulate APCs in the intestine, influencing Treg over TH2 pathways.
What can prevent children from having food allergies?
Exposure to soil, pets and animals - HYGEINE HYPOTHESIS
What can allergy genes and clean environments produce?
Children that produce overly Th2 responses and develop ineffective immune mechanisms causing allergic responses.
What are risk factors for allergy development?
- Immature mucosal immune system
- Early introduction to solid food
- Hereditary increases in mucosal permeability
- IgA deficiency or delayed production
- Inadequate colonisation of the intestinal immune system
- Birth by cesarian.
- Genes favouring TH2 responses
How are allergic reactions to grass divided?
Immediate and late phase responses
What causes immediate phase responses to grass?
Rapid histamine release and leukotrienes
What causes late-phase responses?
Inflammatory leukocyte migration
What are the steps to Dust mite allergies?
- Der p 1 in dust wear away tight junctions and enter the mucosa
- DCs take up antigen, cause Th2 priming
- B cells produce IgE and bind to Mast cells
- Cause degranulation = Allergic response
What does degranulation lead to?
Release of vasoactive amines
What are Type II hypersensitivity reactions induced by?
IgG and IgM
What does Type II hypersensitivity result in?
Antibody-dependent cytotoxicity
What is an example of Type II hypersensitivity?
Hemolytic anaemia
What is phenotypic of Type II hypersensitivity neutrophils?
Frustrated phagocytosis
What causes frustrated phagocytosis?
Neutrophils trying to bind something larger than self.
Release of intracellular enzymes extracellularly
Causes damage to tissues
What are 3 mechanisms of antibody-dependent cytotoxicity in Hypersensitivity reactions?
- Fc receptor-mediated (Fc-IgG)
- Complement lytic pathway (C1q–> MAC)
- C3 receptor mediated
Which receptors do NK cells have?
Low-affinity FcR, which binds to IgG Fc
How do NK cells mediate antibody dependent cytotoxicity?
- Antibody binds antigens on the surface of target cells
- Fc receptors on NK cells recognise bound antibodies
- Crosslinking of Fc receptors signal for NK to kill target cells
- Cells die via apoptosis
Where is ADCC seen in foetuses?
When foetuses possess Rhesus +ve RBCs which counter the mothers Rhesus -ve, causing haemolytic disease of the newborn
What is hemolytic disease of the newborn prevented by?
Rhogam Antibody
When does Type III hypersensitivity occur?
After the formation of large and long antibody-antigen complexes which fail to get broken down by complement/phagocytosis
Where does the accumulation of antigen-antibody complexes occur?
- Glomerulus
- BVs
- Lungs
-Joints
What are some examples of Type III diseases?
- Rheumatoid arthritis, Lupus
What are the effects of immune complex deposition in bV?
- Induce platelet aggregation
- Activate complement
- Neutrophils activate but cannot ingest = damage to BV wall
What are the three types of Type 4 hypersensitivity?
- Contact (latex)
- Delayed (granulomas)
- Gluten sensitivity
What do all Type 4 hypersensitivity responses have in common?
They are all T cell mediated
What is the delayed type 4 hypersensitivity response directed by?
Chemokines and Cytokines released by Th1 cells
What are Th1 cells stimulated to release in the Type 4 hypersensitivity response?
- Chemokines
- IFN-Y
- TNF-a and LT
- IL-3/GM-CSF
What is the process for delayed hypersensitivity to a contact agent?
- Agent penetrates the skin, binds to self-proteins
- DCs and langerhans take up
- Peptides bind to agent are presented to TH1, causing chemokine secretion
- Keratinocytes also secrete cytokines which cause macrophages to activate
- Leads to inflammation
Example of contact sensitivity?
Exposure to poison oak - pentadecacetchol
When are Type 4 granulomas formed?
When intracellular pathogens or their contents cannot be totally eliminated by infected macrophages.
What is the Type 4 granuloma composed of?
A central core made of macrophages.
Surrounded by CD4 TH1 cells.
What do macrophages in the granuloma do?
Release lytic enzymes and cause tissue damage
What is the molecular basis of gluten hypersensitivity?
- Gluten peptides do not usually bind to MHC II
- Tissue transglutaminases deaminate the peptides allowing them to bind to HLA-DQ2 of MHCII
- This presentation activates CD4 T cells
- T cells kill epithelial cells by binding fas. They secrete IFN-y which activates epithelial cells to produce chemokines
What are the pathological features of coeliac disease?
- Destroyed villi
- Cellular infiltrate in the mucosa
- Loss in villi = diarrhoea = loss of nutrient absorption
What is an example of Systemic autoimmune disease?
Systemic Lupus
How is Systemic lupus diagnosed and treated?
- Take cells from blood, fix in formaldehyde
- Mix with cells from patient serum
- Stain to look for anti-DNA antibodies
- Add fluorescent tag to antibodies to visualise which bind to DNA/chromatin/histones/RBCs.
Administer antibodies to the self antibodies for treatment
What is Graves disease?
Uncontrolled activation and overproduction of thyroid hormones - HYPERTHYROIDISM
How does Graves disease occur?
Autoantibodies bind to TSH receptor, mimicking the action of TSH.
Leads to uncontrolled adenylate cyclase activation
What usually stops TSH levels from skyrocketing?
Pituitary recognises the levels and reduces through negative feedback loops
Why does the Pituitary not assist TSH levels in Graves disease?
Has no involvement as stimulation is not TSH dependent
How are autoantibodies for TSH prevented from placental transfer?
Via Plasmaphoresis - which removes maternal anti-TSHR
What is Hashimotos?
Autoantibodies produced to the thyroid antigens themselves - causes HYPOTHYROIDISM
What does Hashimotos cause?
Goitre formation as autoantibodies generate underproduction of Thyroid hormones and the pituitary recognizes this and tries to counter it by producing TSH. Which enlarges the thyroid as a trophic hormone
Where are increases in goitre formation seen?
In populations that live in Mountains due to the lack of iodine.
Iodine uptake is interrupted by Goitre formation
How are immune cells involved in Graves disease?
CD4 T cells help B cells produce antibodies that stimulate and allow the growth and survival of Thyroid cells which leads to an overproduction of hormones
How are immune cells involved in Hashimotos disease?
CD4 Helper T cells help B cells which produce antibodies that cause apoptosis/thyroid cell death.
This causes Hypothyroidism.
CD4 also stim CD8 to destroy cells.
What causes the symptoms of Myasthenia Gravis?
Antibodies bind to ACh receptors which block ACh from binding this leads to no muscle movement due to no NT release.
Antibody-antigen complex formed leads to receptor mediated endocytosis
What happens to the receptors and muscle end plates in MG patients?
They become damaged and degraded over time. This leads to a progressive muscle weakness as muscle contraction can no longer be triggered
How does MG affect new borns?
If the mother has MG, the baby inherits some antibodies. Leads to the baby being born floppy but as antibodies degrade = baby returns to normal.
How is Rheumatoid Arthritis caused?
- Unknown trigger - sets initial inflammation focus as the synovial membrane
- This attracts leukocytes
- Th squeeze through joint tissue via extravasation
4/ CD4 activate Macrophages which produce cytokines and sustain inflammation - Leads to production of MMP and RANK ligands
What is MMP?
Metalloproteinases, nibble away at cartilage
What do RANK ligands to?
Destroy bone
What is the pathogenesis of Inflammatory phase Multiple Sclerosis?
- Unknown trigger causes blood-brain region to become permeable to leukocytes and blood proteins.
- T cells specific for the CNS antigens are activated and reencounter antigens on microglia and DCs
- Inflammation arises due to mast cell + complement activation
- CAUSES DEMYELINATION OF NEURONS
What is the pathogenesis of neurodegeneration phase of MS?
- Glutamate is produced by T cells and APCs
- This injures the neuron and oligodendrocytes
How are statins used to treat M.S?
They block T-cell activation, and they also inhibit metalloproteinase secretion.
They block T cells from entering the CNS
What is another method of blocking T cell movement?
Using antibodies that target 4-integrin
Why does autoimmunity exist?
Self-reactive lymphocyte presence.
Those that are autoimmune fail to regulate them
What are 3 important predictors of autoimmune diseases?
- MHC genotype
- Environmental provocation
- Poor regulation of the Immune system
How does Central tolerance of B cells occur?
- B cells dev in bone marrow
2.B cells that recognize self-antigen on stromal cells are killed. - Once filtered, they go out to the body and bind antigens and activate and migrate to lymph nodes where they form B cells adn memory cells.
How does Central tolerance of B cells occur?
- B cells dev in bone marrow
2.B cells that recognize self-antigen on stromal cells are killed. - Once filtered, they go out to the body and bind antigens and activate and migrate to lymph nodes where they form B cells and memory cells.
How does central tolerance of T cells occur?
- T cell progenitors leave the bone marrow and enter the thymus
- They start to rearrange their Tcr
- Immature T cells that recognize self MHC survive and those that recognise self antigen are killed.
- Mature T cells then enter the body and find antigens on APCs
- These then activate other cells of the immune system through CD4 or kill cells through cd8
What promotes expression of self-tissue specific antigens in the thymus?
AIRE - Autoimmune regulator gene
What does AIRE allow?
Deletion of self-reactive T lymphocytes before they leave the thymus
Why is central tolerance not foolproof?
- Not all self-antigens present in lymphoid regions
- Some weakly self positive T + B cells can escape negative selection
What supports central tolerance?
Regulatory Tolerance
How are tregs formed?
From thymocytes during negative selection of T cells.
Intermediate binding T-cells upregulate FOXP3 TF which actovates a regulatory function in the t cells
