A vaccine for T1 diabetes Flashcards
What are the main symptoms of diabetes
- Thirsty
- Tired
- Toilet
- Thin
What can you test to find information relating to the metabolic status and disease progression of patients with T1DM?
- Genetic variants
- autoantibiodies
- c-peptide
- immune cell subsets
- cytokine response
- biomarkers (methylated DNA) possibly
Describe the stages of T1 diabetes
- Individuals have a genetic predisposition to diabetes
- a precipitating event triggers the onset of overt immunological diabetes
- progressive loss of insulin release
- c-peptide detectable
- no c-peptide detected
What has pathology been associated with T1 diabetes
enterovirus infection
Why is it hard to assess the pancreas
relatively inaccessible organ
What are the roles of the pancreas
- major role: make digestive enzymes
- 2% activity: making insulin
What is the hallmark of T1 diabetes
- patients with T1 diabetes have a system destruction of beta cells in islets of langerhans
How does the immune attack in T1 diabetes work
- immune cells proceed in a very irregular way
- presence of immune cell in the pancreas is abnormal
- immune response is irregular as some beta cells are destroyed while some remain intact
What is the distribution of immune cells in the inflamed islets
- Macrophages
- Lymphocytes
- CD8
- CD4
- cytotoxic b-cells
Describe the pattern of islet immune cell infiltration
- CD8+ mediated cytotoxic response
- as beta cells die off, CD8 cells increase in number
- as CD8 cells increase, insulin decreases
- B cells also infiltrate and multiply alongside T cells
- once insulin production ceases, immune cells continue to circulate still
- destruction of beta cells takes a long time (months-years)
- early intervention could prevent diabetes
What is the relationship between enterovirus infection and diabetes
- the tendency to cause diabetes upon infection isn’t genetic but epigenetic
What is an enterovirus
A virus with a single stranded RNA genome
- genome encodes proteins, many of which create the viral capsid in which nucleic acids are kept
Name some proteins which are a part of the viral capsid
- VP1,2, 3,4
What can VP1 be used for
- VP1 is highly immunogenic
- an antibody for VP1 can be used to study presence of the virus
What does the presence of VP1 in pancreatic cells indicate
- that pancreatic beta cells are susceptible to infection
- enterovirus somehow impairs the functioning of beta cells
Name some cellular antiviral responses specific to pancreatic cells
- protein kinase R (which arrests translation and stops protein synthesis)
- Mda5 and RIG1 (viral genome sensors) which increase interferon expression and prime surrounding cells
- TLRs: increase interferon expression
- Mda5 detects dsRNA and is upregulated in Beta-cells
How has MDA5 been linked to T1 diabetes
has been identified as a critical gene that predisposes T1 diabetes
Which viral sensor has been observed in pancreatic cells with VP1
PKR
How does PKR lead to translational arrest (with diagram)
- ER stress activates GPR78 in the lumen
- active GPR78 phosphorylates PERK in the cytosol
- PERK activates eIF2a to produce proteins
- PKR prevents eIF2a from synthesising proteins by phosphorylating it
- proteins aren’t produced anymore but continue to be broken down
What happens to MLCL2 expression during infection by VP1
- switched off when protein translation is off by PKR
- Mlcl2 is an anti-apoptotic protein
What is inulinitis
- invasion of the pancreatic islets of langerhans by lymphocytes which causes an autoimmune or inflammatory response leading to the destruction of beta cells
What is the normal profile of immune cells in T1 diabetes
- lymphocytes and macrophages have been seen in infiltrated islets
- draw the graph
- seems to be a CD8 cytotoxic mediated response
- CD8 and CD20 move into the cell in parallel
- Both cells are being recruited to islets in parallel and together they mediate the demise of Beta cells
- Profile is consistent with mechanism that both cells play a role and drive Beta cell destruction
- Macrophages follow a similar invasion peak but in less in quantity
- human islets show least amount of CD4 cells
Describe how a viral infection becomes persistent in Beta cells
- some virally infected beta cells evade the immune response
- when virus invades, there a spike in replication of +ve double stranded RNA
- after a few days, this replication is arrested not by an immune response but the beta cells itself (probably its anti-viral responses)
- despite clearance, a small percentage of beta cells remain positive for viral DNA but don’t produce capsid proteins
- therefore, the virus continues to persist in a genomic form (RNA proteins) within the beta cell
Describe the infection of beta cells
Direct cytolytic response - beta cell necrosis - autoimmune beta cells Indirect immune response - viral antigens expressed - beta cell antigens altered - expression of cytokines or HLAs - Autoimmune beta cells
List the differences between acute and persistent enteroviral infection in T1D
Acute infection
- cytotoxic pathway is activated and leads to cell lysis
- involves CD4 and CD8 cells
- release of free virus, viral and beta cell specific antigens
- expression on HLAs
- single stranded
Persistent infection
- persistence of viral RNA and proteins in beta cells
- upregulation of HLA1
- increased visibility of Beta cells to immune cells
- presence of interferon signature
- enhanced response in genetically at-risk individuals
- Stimulation of resting b cell specific antibody production
Describe how you could demonstrate that T1 diabetes is caused by a viral infection
- detection of VP1, dsRNA
- detection of anti-viral cell strategies
- PKR
- Mda5 and RIG1
- TLRs
- Mlcl1 (inhibited by PKR)
Why is there no commercially available vaccine for enteroviral T1D
- no vaccine has been developed yet that recognises enteroviral serotypes in the pancreas
Name a commercially used eneteroviral vaccine
Polio (which isn’t involved in the pancreas)
What is the latest progress made in enterviral T1D vaccines
- a vaccine for coxsackie virus is being tested (safe for mice but not humans)
What can be targeted by an enterovaccine
- a possible genomic approach
- targeting dsRNA in enterviruses
- children should be vaccinated soon after birth before encountering risk
- this way immune system is primed before encounter
- possibly vaccinate those with a genetic risk
How do dsRNA multiply in beta cells
- virus hijack the secretory granule vesicle membranes intended for insulin secretion and use them to multiply
What is the proposed genetic basis of T1D
- known that it’s inherited
- genetic component determines risk level for diabetes
- no mutations included only polymorphisms
- polymorphisms are naturally found in the population and aren’t cell type specific but can cause variations in protein expression
- those with a genetic susceptibility have a greater immune response to viral infection are hence are more likely to get T1D
Name some external factors that can contribute to T1D
- entervirus
- sunlight exposure
- diet
What is the current outlook on T1D
- previously believed that immune cells were the basis
- now believed that beta cells themselves are the problem
- Beta cell get inappropriately attracted to the immune system
- Trigger for this attraction could be external (enterovirus, diet, sunlight exposure) or internal
- Must be a change in cell that makes it visible to immune system
- Immune system response results in T1D
Name two biomarkers for T1D
Markers of autoimmune disease
- Anti-GAD antibodies
- IAA (Insulin auto-antibodies)
