5 - effect of enterovirus on diabetes Flashcards
4 Ts of diabetes
toilet
thinner
thirsty
tired
how many adults have diabetes
422 million
diabetes in on the rise
cost of diabetes to NHS
uses 10% of NHS budget
costs NHS £22 million a day
which diabetes usually has a childood diagnosis
Type 1
what can a blood test via the arm tell you about diabetes
presence of genetic variants, autoantibodies, C-peptide, immune cell subsets, cytokine response, biomarkers (methylated DNA)
gives information about metabolic state of individual and progression of disease
what does a blood test from the arm NOT tell you about diabetes
the cause/causes of the disease (ETIOLOGY)
how can you find the etiology of diabetes
tissue biopsy from the pancreas
role of immunostaining in testing patients with/without diabetes
stain the islets of langerhans to detect for insulin and glucagon production
in T1 diabetes glucagon will remain but there will be barely any insulin
- shows selective elimination of beta cells
immune infiltration of the islets of langerhans
in diabetes immune cells infiltrate the islets in a non-uniform manner
some regions are more targeted than others
e.g. lots of CD8+ T cells and CD20
importance of presence of CD8+ T cells
increase in number in filtrate as insulin concentration decreases
therefore principal mediators of insulin cell death
CD20 flow in afterwards in parallel with CD8
immune cells go away after all beta cells have gone
why is there often a delay in diabetes diagnosis
markers are not present until most beta cells have been destroyed and it is too late
outline the association between enterovirus and type 1 diabetes mellitus
infection with enterovirus may alter immune system increasing susceptibility to diabetes by triggering autoimmunity
Detection of VP1 in individual islet cells in a child with
recent-onset type 1 diabetes
Look in islets of people with T1 diabetes
Cells stain positive for the virus –> suggests that islet cells are susceptible to the virus (can be infected)
If the cells become infected, may be a mechanism by which their functionality could be altered
Viral VP1 was very rarely detected in the islets of children
without type 1 diabetes
detection of viral VP1 in the islets of children
without type 1 diabetes
very rarely detected
Histological evidence that there may be viral infection in beta cells
results of children tested for the virus :
72 have T1 diabetes –> 44 of which have lots of viral protein present in the islets
50 children dont have diabetes –> only 3 had small amounts of viral protein in the islets
evidence that VP1 immunopositivity is restricted solely to beta-cells within the islets
islets were stained to show insulin and viral proteins
viral proteins are not found in glucagon producing cells
which parts of the cell might become activated in virally-infected cells?
Protein kinase R (PKR)
MDa 5
RIG-1
TLRs
role of protein kinase in viral infection
viral response protein
involved in mediation of translational arrest in virally infected cells
(cell switches off protein synthesis to try and dampen down the virus taking over therefore stops virus replicating)
role of Mda 5 in viral infection in patients with diabetes
acts as a viral sensor
recognises single stranded (ss) RNA
expressed at a higher frequency in diabetics
Expression of protein kinase R in islets immunopositive for VP1
greater expression (up-regulated) in virally infected islets
mechanism of PKR
phosphorylates a key factor in the protein synthesis pathway (an initiation factor known as eIFalpha)
this inactivates the pathway and halts protein translation
Therefore any proteins that are rapidly turned over will be continue to be broken down by the cells but not replaced/re-synthesised –> become lost from cells
what is Mcl-1
anti-apoptotic protein
powerful regulator of apoptosis
abundantly expressed in beta cells in islets
Mcl-1 expression in virally infected cells
Mcl-1 is selectively depleted from islet cells expressing VP1
e.g. Mcl-1 is present in neighbouring un-infected cells but absent from those expressing VP1
effects of virally infected cells not having Mcl-1
cells expressing VP1 die because they do not have the anti-apoptotic protein (Mcl-1)
virally infected cells are therefore sensitive to pro-apoptotic stimuli
process of ssRNA production by enterovirus
enterovirus lifecycle
dsRNA intermediate during replication
cells detect dsRNA as foreign
could dsRNA be used as a marker of or means to monitor infection
dsRNA sense by mda5
positive and negative RNA in double stranded formation was found present in muscle of mice with chronic inflammatory myopathy (CIM)
(Tam et al 1999)
dsRNA is also detectable in islet beta cells with T1 diabetes –> shows they are virally infected
dsRNA not present in alpha cells with T1 diabetes
Mda 5 expression in non-diabetic controls
Mda 5 is present
present mainly in alpha cells
not much Mda 5 in beta cells in controls
is diabetes an infectious disease
no
main feature of T1 diabetes
autoimmune
which two cell types mainly mediate decrease of beta cells
CD8+ T cells
CD20+ T cells
effects resulting from persistent viral infection
evasion of normal immune mechanisms so virus isn’t fully cleared
some beta cells remain +ve for viral RNA and do not produce viral capsid protein allowing virus to hide genomically
therefore virus persists in the genomic form in the beta cells as RNA
what triggers beta cell death
environmental agents acting in the context of an already susceptible genetic background
immune cell destruction of beta cells
autoimmune
recognise beta cells as foreign
many immune cells work together
immune cell count decreases to 0 after beta cells have died
beta cell autoantigens
released from beta cells after damage
processed and presented to helper T cells by APCs
role of macrophages in beta cell destruction
antigen presenting cells
first cells to infiltrate islets
release IL-2 to activate CD4+ T cells
produce ROS
role of cytokines in beta cell destruction
bind to receptors on beta cells to activate MAP-kinases and T factors
signalling cascades initiated (NFkB and STAT-1)
results in functional impairment and endoplasmic reticulum stress
apoptosis
what activates CD8+ T cells
IL-2 produced by Th1 cells
