Animal models in MS Flashcards
Outside in cause - virus
Outside cause:
Virus infects the body, viral Ags are bring to LN, and it’s been known that there’s some autoreactive cells in our body that’s failed to be eliminated, and they get activated too (due to similarity in epitopes with pathogen – a pathogen epitope is too similar with a body epitope) then they go to blood, then CNS. In BBB, when there’s inflammation, T and B cells leak inside. Then they teach the epitope to local APCs, and myelin is targeted
Animal model - definition
A model organism is a non-human species that is studied to understand biological phenomena, to get insight into workings of human disease.
All models are wrong, but some are useful. There’s no animal model that completely reflects MS.
Validity criteria for animal model
Validity: Degree of capability that a model can replicate the original human disease
Face validity: Model and human symptoms/pathology should look more or less the same.
Construct validity: Degree of similarity between mechanisms of a disease
Predictive validity: Ability of a model to correctly identify efficacy of therapy
While evaluating predictive validity we have to realize that in mice models, we induce a disease from the beginning and check the therapy – but in actual patients we try to stop an ongoing malignancy = different.
External validity: The way results obtained using a particular model, whether it can be repeated in another lab or model
MS disease induction methods on animal models
Chemical agents to kill oligodendrocytes
(inside out model)
Virus infection eg. Theiler’s (outside in model)
Active immunization: EAE (outside in model)
Passive immunization: T cell transfer (outside in model)
Creation of transgenic TcR or BcR
(inside out model)
EAE creation + clinical course
EAE creation:
myelin emulsion / components of myelin (MOG/PLP/MBP) Obv added to an adjuvant to induce autoimmunity against it, follow up.
Clinical course below: Relapsing remitting disease course. 3 acute attacks, remission/relapse. 4th attack = no relapse anymore, chronic. Mouse goes different parts of paralysis of body.
Passively induced T lymphocyte administration EAE model
You have a mouse, you induced disease on it in same way, take spleen + LN, re-stimulate them in ex vivo, inject it to another mouse. You can induce the disease on another mouse.
You can take T cells out from any mice, inject it to another mice, and see if there’s a defect in T cells or something.
Transfer of T cells alone or activation of T cells alone = is not enough to get the MS pathology. It requires both T and B cells. When T cells enter to LN, shown in passive model, induces inflammation, but to get demyelination = you definitely need Abs. Infiltration of Abs is also dependent on T cells.
1) Inflammation with both T/B cells
2) Demyelination w Abs
Predictive validity of EAE + why there’s problems
When you give a drug to mice, you expect it to be working in humans too if it’s a valid model. = That’s not the case. Sometimes it works, but mostly it doesn’t. When they found EAE, they thought they will find the cure, but very effective drugs in mice model didn’t do anything in patients.
Should we even use this model?
There’s many differences between mice and humans. = needs translational research. Also mice are inbred, they only represent 1 genetic background. And they are raised in a sterile environment.
Pathogens have a huge impact on human immune system though. = So immune systems are also very different. That can explain this translational problem.
Inside out concept validation
EAE in marmosets - MOG
Marmosets are selected. They are distant to animals genetically, but they have good immunological overlap.
They have human like, pathogen educated immune system - not raised sterile
They have herpesvirus infections, CMV and EBV equivalent CalHV3
Used when adults
Have human like MRI
Very little monkeys.
Outbred/unique genetics
MS works well, relapsing remitting/2nd progressive stages all can be observed. Also RRMS comes before 2nd progressive, so like humans. Lesions show demyelinations, innate
immune cells + lymphocytes.
Demyelination is profound – clear white spots. Gray matter also has lesions. Whole surface is demyelinated = that’s how MS looks too. All lesions you can found in MS brain are also found in marmoset EAE.
Also T lymphocytes are seen = in parenchyma(inside) and meninges (membrane). Panel G. Few B cells in meninges and parenchyma. Macrophages macroglia are abundant.
They found MOG: myelin oligodendrocyte glycoprotein: found to be very critical in disease process for every monkey. If you CKO that from myelin, no mice gets MS.
They also found out that EAE onset is related with amount of T cell response: if you have more T cells you get earlier onset.
They also saw that not every lesion leads to pathology. Monkeys get clinical symptoms when lesions also start to grow from white matter to gray matter.
pathogen educated immune system human vs mice / memory naive T cell
Naïve immune cell compartment empties as we get old. Known from vaccination studies, response of elderly to vaccination is lower, because of this. The cells that aren’t stimulated for life, just disappear and never reproduced again.
On the other hand, oligoclonal expansion of memory cells are observed in elderly. Eg. for CMV. 80-90 y.o. people memory compartment %30 is for controlling CMV. If this can’t be controlled = you might die from CMV. These memory cells are hyperactive, and take over all memory compartment. = Senescent immune profile. Compartment that protects us for new viruses decrease in size, but the ones that keeps the old infections in control increase.
Mice: only naïve cells. Memory is completely empty. Really shows the difference between adult humans and mice. The time that these autoimmune diseases happen in people, entire cells are in memory compartment.
Human MS model vs Marmosets outside in + MOG
Induction of lesions in preclinical phase occurs via an autoimmune mechanism, happens due an adjuvant + myelin injection = Outside in model in EAE. It activates Thelpers that drive inflammation, and B cells that can induce demyelination more. Signature is IFNgamma, and origin is naïve!
Human MS pathway: Occurs for another MOG epitope. Signature is IL-17. T cells driving this are effector memory T cells from CMV controlling repertoire!
Human MOG and marmoset MOG epitopes are so close to one another and both are extremely conserved.
MOG + oil (no adjuvant) = causes no disease in mice
In marmosets, causes full blown disease.
All pathology is observed = oligodendrocytes are disappearing due to CTL killing = more demyelination
Virus molecular mimicry study with rhesus monkey
CMV epitope is very similar to rhesus MOG. = molecular mimicry from viruses
Mouse EAE vs monkey EAE progression pathway vs human MS
Mouse like EAE = activated by immunization. TH1 and B cells = inflammation, demyelination. Acute. Abs against myelin recruits macrophages/complement to induce myelin death. Normal demyelination pathway observed.
There’s another pathway though = seen in monkeys/humans = CTL kills oligodendrocytes and stops myelin additionally. = EAE progression pathway. Lacking in mice but seen in marmosets, it’s very similar to MS.
Can EBV start MS? - marmosets model
EBV is a virus mainly infects B lymphocytes.
B cells drive MS: Rituximab works well in inhibiting disease progression in relapsing remitting.
Anti-CD20 therapy completely suppresses disease almost %100 in marmosets EAE progression pathway. Eventhough B cells were almost completely depleted from circulation and LN, complete suppression of disease isn’t observed with anti-Blys and APRIL. Only a delay in disease onset is observed.
Why? Anti-CD20 completely depleted the viruses.
But anti-blys and Anti-April couldn’t remove all EBV from body. EBV infected B cells are immortalized, so it’s normal that they don’t need these cytokines for survival.
MS immune pathology - recent findings
Microglia nodules: Before there’s any sign of autoimmune activity in white matter, you already see clusters of activated microglia. A proportion of these microglia start lesions.
Topical swellings of myelinated axons: 3 types. Blister, bleb, deg.
In blister, myelin dissociates from axon, axon is normal. In bleb, axon swells.
In deg. Axon gets degenerated ,and myelin dissociates
Blisters:
Blisters are also seen in other diseases like Alzheimers or in old age, but less. Causes of blisters are complicated.
There’s altered distribution of molecules that are necessary to firmly bind axons to myelin = myelin itself also changed and got a posttranslational modification called citrunillation. Arg residues replaced with Citrulline. So myelin is less compacted and dissociating.
Citrunillation also makes myelin immunogenic
