Smouldering MS: Is 20 years a long time?


Barts-MS rose-tinted-odometer: zero stars or one ★ depending on your disposition

I prepared this post not knowing that Prof. Laura Airas has submitted a guest post in response to a request from the Mouse Doctor. Before reading this post please make sure you read her blog post first. It provides an important counterbalance to my contrarian view below. Thank you.

More than 20 years ago, when I was a junior researcher, doing my PhD,  I started a research collaboration with Dr Richard Banati, who worked in the Queen Square Brain Bank and the Imperial College PET imaging unit. Richard was investigating activated microglia in multiple sclerosis. The collaboration was very fruitful and led to the very first study of an imaging molecule called PK11195  that could label activated microglia. 

In the study (see below), we elegantly showed that people with MS (pwMS) had widespread microglial activation in their brains. Their brains, in fact, lit up like Christmas trees with so-called ‘hot’ or activated microglia. The assumption, which is now dogma, from this and other studies is that these microglia must be bad for pwMS. This has led to many research and drug discovery programmes to find treatments to switch off hot microglia.   

PK11195 labelling hot microglia. From Banati et al.

Now dial forward 20 years and finally, a follow-up study from Finland that shows that pwMS with a lit Christmas tree in their heads do worse in the longterm, i.e. pwMS with more microglial activation as determined by PK11195 staining had more disease progression that was independent of relapses. The implication is that PK11195 is a good marker of smouldering MS and if we switch off this marker we will improve long-term outcomes. 

In an email exchange with colleagues, I challenged this thinking. Is the PK11195 signal, or hot microglial response, the chicken or the egg? The microglial response may not be causal but simply associated with a worse outcome in MS. Just maybe the microglia are responding to what is causing MS and are not the primary drivers of the MS pathology. Therefore if you switch off the microglial response you may not improve MS outcomes but actually make them worse. 

I even provided some early odds of this happening. I predicted that a drug that switches off the microglial response had only about a 20% chance of improving MS outcomes. I balanced this by saying that I thought that a microglial inhibitor had about a 60% chance of actually making MS worse. I was then challenged that these odds were simply a guess; like an unskilled poker player. I disagree. Firstly, poker is a game of skill and the most skilled poker players make a relatively decent living from their skills. Secondly, there is a scientific process behind making accurate predictions (see post-script), which I try to apply. Finally, we need to apply science to the microglial prediction at hand. 

The Science: In the smouldering or slowly expanding MS lesion the hot microglia are lined up like soldiers fighting an enemy at the edge of the lesion. They remind me of a Greek phalanx.

A Military Phalanx

These microglia are not malignant cells, which makes me think they are simply doing their job. Now what if these microglia are responding to something in the surrounding tissue, for example, a slow viral infection? Switching them off may actually make the slow viral infection worse. In addition, microglia have very important function clearing up debris in the nervous system and maintaining the health of synapses and neurons in general. 

Figure 1 (from Frischer et al., Ann Neurol 2015): (A, B) Early active plaques (EAL) were defined by macrophages immunoreactive for minor myelin proteins (MOG positive macrophages right insert in A) as well as major myelin proteins (PLP positive macrophages left insert in A). (C, D) Smoldering plaques (also called slowly expanding plaques) typically showed a rather inactive centre with no or few macrophages, surrounded by a rim of activated microglia. Only few of these macrophages or microglia cells contained early myelin degradation products. Inserts depict plaque edge. (E, F) Inactive plaques revealed a sharp plaque border without or only few macrophages or activated microglia (insert). (G, H) Completely remyelinated plaques typically containing few macrophages without early myelin degradation products were classified as shadow plaques. Shadow plaques presented with a sharp plaque edge and were associated with fibrillary gliosis.

More Science: Importantly, defects in the signalling pathway of CSF-1 (colony-stimulating factor 1), which is also known as macrophage colony-stimulating factor (M-CSF), cause progressive dementia and disease of the cerebral white matter called a leukoencephalopathy. CSF-1 is a microglial stimulant. This is a warning that inhibiting microglia indiscriminately is unlikely to be good for the brain and particularly a damaged MS brain. This is why I have given greater odds to a microglial inhibitor making MS worse than making MS better. 

I am also aware that there are different types of microglia, different types of microglial responses and hence we may have to be more selective in how we target microglia in MS. Despite this, I think we as an MS community need to take a step back and challenge the current dogma that the microglial response in MS is necessarily bad. If we don’t we may be unpleasantly surprised and disappointed with the outcome of clinical trials targeting hot microglia and smouldering MS. 

P.S. If you are interested in reading about the science of prediction I would recommend ‘Superforecasting: The Art and Science of Prediction’ by Dan Gardner and Philip Tetlock; a remarkable book that provides important insights and lessons to avoid unconscious biases and it teaches you a little poker as well 😉 

Sucksdorff et al. Brain TSPO-PET predicts later disease progression independent of relapses in multiple sclerosis.  Brain, awaa275, Published: 02 October 2020.

Overactivation of microglia is associated with most neurodegenerative diseases. In this study we examined whether PET-measurable innate immune cell activation predicts multiple sclerosis disease progression. Activation of microglia/macrophages was measured using the 18-kDa translocator protein (TSPO)-binding radioligand 11C-PK11195 and PET imaging in 69 patients with multiple sclerosis and 18 age- and sex-matched healthy controls. Radioligand binding was evaluated as the distribution volume ratio from dynamic PET images. Conventional MRI and disability measurements using the Expanded Disability Status Scale were performed for patients at baseline and 4.1 ± 1.9 (mean ± standard deviation) years later. Fifty-one (74%) of the patients were free of relapses during the follow-up period. Patients had increased activation of innate immune cells in the normal-appearing white matter and in the thalamus compared to the healthy control group (P = 0.033 and P = 0.003, respectively, Wilcoxon). Forward-type stepwise logistic regression was used to assess the best variables predicting disease progression. Baseline innate immune cell activation in the normal-appearing white matter was a significant predictor of later progression when the entire multiple sclerosis cohort was assessed [odds ratio (OR) = 4.26; P = 0.048]. In the patient subgroup free of relapses there was an association between macrophage/microglia activation in the perilesional normal-appearing white matter and disease progression (OR = 4.57; P = 0.013). None of the conventional MRI parameters measured at baseline associated with later progression. Our results strongly suggest that innate immune cell activation contributes to the diffuse neural damage leading to multiple sclerosis disease progression independent of relapses.

Banati, …., Giovannoni,….et al. The peripheral benzodiazepine binding site in the brain in multiple sclerosis: quantitative in vivo imaging of microglia as a measure of disease activity. Brain 2000 Nov;123 ( Pt 11):2321-37. doi: 10.1093/brain/123.11.2321.

This study identifies by microautoradiography activated microglia/macrophages as the main cell type expressing the peripheral benzodiazepine binding site (PBBS) at sites of active CNS pathology. Quantitative measurements of PBBS expression in vivo obtained by PET and [(11)C](R)-PK11195 are shown to correspond to animal experimental and human post-mortem data on the distribution pattern of activated microglia in inflammatory brain disease. Film autoradiography with [(3)H](R)-PK11195, a specific ligand for the PBBS, showed minimal binding in normal control CNS, whereas maximal binding to mononuclear cells was found in multiple sclerosis plaques. However, there was also significantly increased [(3)H](R)-PK11195 binding on activated microglia outside the histopathologically defined borders of multiple sclerosis plaques and in areas, such as the cerebral central grey matter, that are not normally reported as sites of pathology in multiple sclerosis. A similar pattern of [(3)H](R)-PK11195 binding in areas containing activated microglia was seen in the CNS of animals with experimental allergic encephalomyelitis (EAE). In areas without identifiable focal pathology, immunocytochemical staining combined with high-resolution emulsion autoradiography demonstrated that the cellular source of [(3)H](R)-PK11195 binding is activated microglia, which frequently retains a ramified morphology. Furthermore, in vitro radioligand binding studies confirmed that microglial activation leads to a rise in the number of PBBS and not a change in binding affinity. Quantitative [(11)C](R)-PK11195 PET in multiple sclerosis patients demonstrated increased PBBS expression in areas of focal pathology identified by T(1)- and T(2)-weighted MRI and, importantly, also in normal-appearing anatomical structures, including cerebral central grey matter. The additional binding frequently delineated neuronal projection areas, such as the lateral geniculate bodies in patients with a history of optic neuritis. In summary, [(11)C](R)-PK11195 PET provides a cellular marker of disease activity in vivo in the human brain.

CoI: multiple

Twitter: @gavinGiovannoni  Medium: @gavin_24211

About the author

Prof G

Professor of Neurology, Barts & The London. MS & Preventive Neurology thinker, blogger, runner, vegetable gardener, husband, father, cook and wine & food lover.


  • Can I please just add that TSPO is also expressed by some astrocytes and not necessarily just by bad microglia. I think we still need more information on what TSPO does. Just a thought.

  • Prof G,

    Thanks for your post.

    I’ve followed your posts for some time. I think your position is as follows:

    – relapses caused by focal inflammation are not MS they are just a response (from the external immune system) to something going on in the brain:

    – hot microglia / smouldering MS are not MS they are just a response (from the brain’s immune system) to something going on in the brain.

    – the ‘something going on in the brain’ is probably a virus, and the evidence so far points to EBV.

    Given the above, therapies which tackle relapses and the response of the innate immune system are unlikely to address the cause of MS (a virus) or significantly change the outcome (accumulating disability) for the patient.

    I have 2 questions:

    – are there any trials underway to tackle the virus (likely to be driving the responses of the immune systems)?

    – if you are right in your thinking, why do you get involved in trials to tackle relapses when you believe that relapses are just a response to what is driving the disease (a virus)?

    • Re: “… are there any trials underway to tackle the virus (likely to be driving the responses of the immune systems)?”

      Yes, I have just heard that a group in the US has funding to do a HAART (highly-active antiretroviral treatment) trial in MS. We have been wanting to do this study for the last 6-years and have had 3 grants turned down (low self-esteem). Please note that HAART also targets EBV (data presented at last ECTRIMS). Because of my interest in this strategy, I have been asked to join the advisory committee of this study (good news for me).

      ATARA Bio is testing anti-EBV cytotoxic T-cells as a treatment in MS. They are about to start their phase 2 programme (disclosure I am a scientific advisor to ATARA).

      Our group is starting a trial of famciclovir to target EBV; this is an exploratory trial and will only provide proof-of-concept data.

      We are testing cladribine, which is CNS-penetrant, and a CNS-penetrant proteasome inhibitor for their impact on intrathecal* B-cells to see if they can clear the CNS of potentially EBV-infected B-cells.

      I am also trying to get an induction-maintenance study of anti-CD20 followed by an antiviral drug off the ground; this trial design is based on the EBV hypothesis.

      There are also other EBV targeted trials going in oncology, i.e. drugs that target for example EBNA-1 that may be suitable for repurposing to MS.

      So in summary, yes there is some activity going in MS to tackle the viral hypothesis, but clearly not enough.

      * intrathecal = within the meninges

      • Just want to say that this is a great summary from Sid and the reply is hugely informative as well. So how long have we got to ‘hang tough’ whilst waiting for these studies to yield some results? 3-5 years?

      • CNS-penetrant proteasome inhibitor for their impact on intrathecal* B-cells to see if they can clear the CNS of potentially EBV-infected B-cell

        Safety of Ixazomib Targeting Plasma Cells
        in Multiple Sclerosis
        G. Struga, L. Bianchi, F. Ammoscato, J. Bestwick,
        G. Giovannoni, S. Gnanapavan
        Blizard Institute, London, United Kingdom
        Background and aims: Ixazomib, a proteasome inhibitor,
        is licensed for the treatment of multiple myeloma, a
        malignant plasma cell disorder. In MS, the production of
        antibodies by plasma cells and B cells play a critical role in
        its pathogenesis and disease progression.
        The purpose of this study is to investigate the safety of
        ixazomib and if it can reduce or clear oligoclonal bands
        (OCBs) from the cerebrospinal fluid in MS.
        The Phase Ia/IIb trial using Ixazomib will be carried out in
        relapsing remitting multiple sclerosis, primary progressive
        multiple sclerosis and secondary progressive multiple
        sclerosis. The primary outcome will be safety, followed by
        effect on cerebrospinal fluid OCBs.
        Methods: It is a double-blind, randomised and placebo ed
        control trial with 76 participant (50 on active drug; 26 on
        placebo) for up to 24 months. 1 cohort of patients (n=38)
        will have relapsing MS and the other cohort (n=38) will
        have progressive MS.
        Measures of adverse events will be compared between
        active and placebo. The efficacy will be measured with the
        proportion of OCB IgG compared between active and
        placebo. The outcome will be monitored with sequential
        MRI and EDSS comparing the treatment group to placebo.
        Results: The trial is due to commence in early 2020.
        Conclusion: The trial will be targeting a novel disease
        pathway in MS; that of long lived plasma cells. There is not
        any convincing evidence yet that currently DMT eliminate
        intrathecal OCB. If successful it would be the first drug of
        its kind to be used in MS.
        Disclosure: Nothing to disclose

        Phase 1 ?

    • Re: “.. if you are right in your thinking, why do you get involved in trials to tackle relapses when you believe that relapses are just a response to what is driving the disease (a virus)?”

      Firstly, my position is currently based on a hypothesis. I may be wrong. It is never good science or practice to change your behaviour before you have the evidence to do so.

      Secondly, how do you think I have formed my opinions about smouldering MS? By participating in clinical trials and learning from them.

      Your use of the term ‘believe’ sums things up for me. It is not about believing; people who believe are unable to change their worldview. To quote John Maynard Keynes, the famous British economist responsible for ‘Keynesian economics’: “When the facts change, I change my mind. What do you do, sir?”. I will change my mind and practice when the facts change; MS is autoimmune until proved otherwise 😉

  • ” Importantly, defects in the signalling pathway of CSF-1 (colony-stimulating factor 1), which is also known as macrophage colony-stimulating factor (M-CSF), cause progressive dementia and disease of the cerebral white matter called a leukoencephalopathy. CSF-1 is a microglial stimulant. This is a warning that inhibiting microglia indiscriminately is unlikely to be good for the brain and particularly a damaged MS brain. This is why I have given greater odds to a microglial inhibitor making MS worse than making MS better. ”

    And yet……..Increased expression of colony-stimulating factor-1 in mouse spinal cord with experimental autoimmune encephalomyelitis correlates with microglial activation and neuronal loss.

  • BTKi are claimed to inhibit microglia activation. There should be done phase 2 data on them at least Merck and Sanofi and I don’t recall having read anything of going worse.

    I think that the disease can be triggered by viral infection or insult. It would be strange that we have not found the virus yet. Also, once the autoimmune response is established by this virus the response is self feeding and will not stop until it is blocked.

    If the microglia is responsible why alemtuzumab or AHSCT can stop the disease if they don’t get to the brain?
    If the microglia is not responsible why people that go negative on OCB do better also in the long term?

    There are many questions, but we need one answer that fits everything.

    We should also look at the histology, where we have microglia we have also antibodies. So microglia could be the good and the bad guy at the same time in MS. Shutting it is the only way to see what happens.

    • Central Effects of BTK Inhibition in Neuroinflammation
      Ross C. Gruber1, Nathalie Chretien1, Michael R. Dufault1, Jonathan Proto1, Mindy Zhang1, Michael LaMorte1, Evis Havari1, Tarek A. Samad1, Timothy Turner1, Anthony Chomyk2, Emilie Christie2, Bruce D. Trapp2, Dimitry Ofengeim1
      1Sanofi, 2Cleveland Clinic
      To assess the role of Bruton’s tyrosine kinase (BTK) signaling in modulating inflammatory processes in microglial cells in vitro and in vivo.
      Innate immune activation in the central nervous system (CNS) has been proposed to be a key driver of disease progression in multiple sclerosis (MS). BTK is expressed in B cells and innate immune cells, including macrophages and microglia. In B cells, this kinase is an essential component of the B-cell receptor signaling pathway regulating proliferation, maturation, antigen presentation, and production of secreted immunoglobulins. We hypothesize that in addition to its role in B cells, BTK regulates microglial deleterious inflammatory signaling; therefore, inhibiting BTK with a brain-penetrant inhibitor may provide therapeutic benefit within the CNS by targeting innate immunity associated with disease progression in MS.
      RNA sequencing, immunohistochemistry, and Western blotting were used to measure BTK or phospho-BTK in primary mouse microglial cell lines, mouse brains, or postmortem human MS brains.
      We demonstrated basal activity of BTK in murine microglial cells in vitro that was enhanced by stimulation with immune complexes and silenced with a BTK inhibitor. Transcriptome analysis was used to generate a microglial gene expression signature of BTK signaling, identifying unique RNA biomarkers of BTK activation or inhibition. This novel BTK-dependent transcriptional profile was confirmed in vivo, using direct stereotaxic injection of aggregated IgG to mouse brain. Oral administration of a brain-penetrant BTK inhibitor downregulated the BTK-dependent gene expression signature in mouse brain. In tissue derived from autopsy specimens, immunohistochemistry studies coupled with single-nucleus RNA sequencing demonstrated that BTK was expressed in B cells as well as in microglial cells, with increased levels in MS lesion samples.
      BTK-dependent inflammatory signaling in microglia can be modulated using brain-penetrant BTK inhibitors, which could abrogate microglia-driven neuroinflammation implicated in disease progression in MS

  • Moved for wrong post
    October 9, 2020 at 1:44 pm

    After 20 years of your findings and then getting confirmation of YOUR discovery. Do you think this will inspire hope or frustration in people with MS. Do you understand the paranoia this creates that promising MS research is deliberately being burried by pharama in order to prevent a cure from being found? If I was the researcher that made a discovery and allowed nothing to happen for 20 years to end the suffering caused by this disease to patients and their families. I would find my culpability in this sad states of affairs undeniable and spend what time I have making things right. But I am well aware the lure of money and the things we will do to get it and by no means a perfect angel myself. But well done for being vindicated after 20 years and whatever kudos that it gives you.


  • Immune reseting microglia

    Triggered by trauma, microglia—the brain’s immune cells—morph into an inflammatory state, which helps to protect the brain. However, long-term inflammation after TBI may contribute to neurological degeneration and cognitive declines similar to those observed in TBI-associated neurodegenerative diseases, such as chronic traumatic encephalopathy and Alzheimer’s disease.

    The scientists involved in the new study found that highly delayed targeting of chronic inflammation pathways may be a very effective therapeutic strategy for TBI.

    One month after a TBI, the team inhibited a particular receptor microglia need to survive. The inhibition killed 95% of the mice microglia cells. However, the cells bounced back to normal levels once the inhibition ends.

    The researchers then stopped the inhibition after one week and let the mice recover for a few months. They found that the inhibition essentially “reset” the mice’s microglia: the new cells were in a more normal, less inflammatory state. The mice recovered better than the mice that didn’t receive treatment, showing less brain damage, fewer neuron deaths, and better motor and cognitive performance.

    Its Almost an IRT theraphy in the brain

  • What is your evidence pf Ebv in the brain?

    The Epstein-Barr antibody paradox in
    Multiple Sclerosis

    Background and aims: Increased levels of serum and
    cerebrospinal fluid (CSF) antibodies against morbilli,
    varicella zoster and rubella, and increased serum antibodies
    against Epstein-Barr virus (EBV), are common features of
    MS. Paradoxically, several studies showed that the level of
    antibodies against the Epstein-Barr nuclear antigen 1
    (EBNA1) is low in the CSF, which may be due to immune
    evasive properties of EBNA1 or to low level of exposure of
    this antigen in the central nervous system. Our objective is
    to determine whether low CSF antibody levels against
    EBNA1 also apply to an immunodominant viral envelope
    EBV antigen, gp350.
    Methods: The level of anti-gp350 IgG was determined in
    serum and CSF in MS patients (n = 23) and healthy controls
    (n = 18) by an ELISA using a recombinant gp350 antigen
    The antibody index was calculated as adjusted QOD (QOD/
    (total IgG CSF/total IgG serum)).
    Results: The serum concentration of anti-gp350 IgG was
    higher in the MS patients. The CSF antibody index (adjusted
    QOD) for gp350 was significantly lower in the MS patients
    (0.070) than in the healthy controls (0.142, p<0.001). We
    obtained similar results if we included EBV seropositive
    controls only.
    Conclusion: Our finding of low CSF gp350 antibody index
    is consistent with other reports on the EBV antibody
    paradox in MS, arguing against antigenic exposure of this
    virus in the central nervous system. Interaction with EBV in
    MS pathogenesis might be confined to the peripheral
    immune system.

    • It may not be in the brain but in the periphery. However, our group did find low levels of EBV in active MS lesions and it was associated with a type 1 interferon signature. So the jury is out on this. EBV may transactivate HERVs who are then the main driver of CNS damage or EBV simply lowers the threshold of B-cell activation. The biology around EBV and what it does to B-cells is really fascinating and needs a deep think and a lot more lab work.

    • J S Tzartos 1, G Khan, A Vossenkamper, M Cruz-Sadaba, S Lonardi, E Sefia, A Meager, A Elia, J M Middeldorp, M Clemens, P J Farrell, G Giovannoni, U-C Meier. Association of innate immune activation with latent Epstein-Barr virus in active MS lesions. Neurology 2012 Jan 3;78(1):15-23. doi: 10.1212/WNL.0b013e31823ed057. Epub 2011 Dec 7.

      Objective: To determine whether the activation of innate immune responses, which can be elicited by pathogenic and endogenous triggers, is associated with the presence of Epstein-Barr virus (EBV) infection in the multiple sclerosis (MS) brain.

      Methods: White matter postmortem MS (n = 10) and control tissue (n = 11) was analyzed for the expression of the proinflammatory cytokine interferon α (IFNα) by immunohistochemistry and for EBV by using the highly sensitive method of EBV-encoded RNA (EBER) in situ hybridization.

      Results: We detected overexpression of IFNα in active areas of white matter MS lesions but not in inactive MS lesions, normal-appearing white matter, or normal brains. The presence of IFNα in macrophages and microglia (expressing human leukocyte antigen class II) is suggestive of local production as part of an acute inflammatory process. Interestingly, EBERs were also specifically detected in areas where IFNα was overexpressed in these preselected active MS lesions. EBER+ cells were also found in CNS lymphoma and stroke cases, but were absent in other control brains. We next addressed a potential mechanism, e.g., the role of EBERs in eliciting IFNα production, and transfected EBERs into human embryonic kidney (HEK) cells. We used HEK cells that stably expressed Toll-like receptor-3, which recognizes double-stranded RNAs, associated with many viral infections. EBERs elicited IFNα production in vitro.

      Conclusion: These findings suggest that latent EBV infection may contribute to the inflammatory milieu in active MS lesions by activating innate immune responses, e.g., IFNα production. Unraveling the underlying mechanisms may help in uncovering causal pathways and developing better treatment strategies for MS and other neuroinflammatory diseases.

By Prof G



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