The micro-clot finding in Long Covid — implications for the possible aetiology of ME/CFS

Indeed, where is the Budd-Chiari liver enlargement or the ventilation perfusion mismatch or reduced GFR?

 

@Jonathan Edwards

Do you know if micro clotting is the result of a persistent infection?

 

Microclotting occurs in subacute bacterial endocarditis. It may occur in other infections but nothing obvious comes to mind immediately.

Remember that what has been reported by Pretorius et al is clotting in a tube rather than clotting in a patient. Clotting occurs in acute severe Covid19 but I have not seen evidence that would go with microblogging in patients in LongCovid. There seems to be an increased risk of some thrombotic events like venous thrombosis of pulmonary embolism but that may just relate to inactivity and generally being unwell.

 

Yes — some conjecture:

What we see is a mixture of anecdotal reports of some people recovering and some not recovering, but from what I've read many do report symptomatic improvement on this combined anticogualant / antiplatelet regimen. I think it's important to note that the combination may be having a positive symptomatic effect, but that people (including on S4ME) report no benefit to long-term ME on a single agent, eg "I was on aspirin or warfarin or rivaroxiban" etc.

I think what this is all pointing to is that the microclotting observation is a downstream effect. It may be genuinely reflecting hypercoagulability, but as Jo says this is clotting in a tube and we don't know if microclots are happening in vivo. It may be a specific feature of LC, or a lesser feature of ME, or present in both but simply something that largely resolves with time even as the underlying ME/LC persists.

I'm running with the idea that "something in the blood" is generated or upregulated — maybe not a lot (so we haven't properly taken notice), but constantly — enough to have major physiological effect over sufficient time. That something has a wide area-of-effect: say the entire vascular lining resulting in endothelial dysfunction; and impairments to some contents of the blood, eg lymphocytes and platelets. That results in many deleterious effects, just one of which might be hypercoagulability which is symptomatically, and maybe also pathogenically, cumulative.

Reducing the hypercoagulability might help with the symptoms, something the patients notice. But it doesn't of itself stop the generation of the something-in-the-blood. That process may simply resolve with time in some, but the treatment regimen is erroneously given credit for this rather than simply some symptomatic relief. (If hypercoagulability somehow also up-regulates the something-in-the-blood as a feed back, then yes it may also be helping).

Aside: I see the team put out a preprint earlier in the week, where they demonstrate the effect via an imaging cytometer. However, I don't think this advances things much or even at all. They again used platelet-poor plasma in citrate tubes, with Thioflavin T and were correlating their prior method with the new one. They suggest that a standard lab (non-imaging) cytometer could also be used as a high throughput assay (counting objects of x-y size), which I presume would be in the absence of ThT. I don't know if that could work with citrated whole blood. They say this is the first attempt to use a cytometer to analyse a non-cell.

I think their idea is that generally flow is impaired rather than blocked blocked? They describe the microclots as resistant to breakdown, but I think also nebulous or at least deformable. Then they would be a bit like a red or white cell that adjusts to fit through the smaller capillaries. Over the capillary network, general vascular flow and flow control might then be degraded (adding to the probably more important NO reduction / endothelial dysfunction).

They always say that the capillaries are blocked, preventing oxygen getting to the tissues - QED. I don't think so simple, although maybe it's contributing. I think the metabolic reprogramming is the primary event — eg the Warburg effect of aerobic glycolysis and reduced fatty acid oxidation etc across many tissues, but perhaps in particular affecting endothelium and lymphocytes.

I haven't looked at liver, but for lungs and kidneys:

Pulmonary Dysfunction after Pediatric COVID-19 (2022, Radiology)

Persistent 129Xe MRI Pulmonary and CT Vascular Abnormalities in Symptomatic Individuals with Post-acute COVID-19 Syndrome (2022, Radiology)

Kidney Outcomes in Long COVID (2021, J Soc Am Nephrology) —

 

Seeing particles in blood in living people is not easy, although you can see red cells moving in retinal vessels with the right equipment I think. (You can see them in yourself with a clever trick with a light shining on to your eyeball from the side while you wiggle it.)

But a reasonable ask would be to see these particles in freshly drawn whole blood, without any processing.

I may be wrong but I think one can argue like this:
If these particles are able to block capillaries they will be of the same size as white blood cells or larger and would be visible on a Coulter counter. The Coulter count shines a fine light beam on to a stream of cells and measures the size and character of each cell separately using forward scatter and side scatter. You can get more information by staining cells with fluorescent dyes but that introduces potential artefacts. Let's stick with Coulter. The Coulter machine counts cells of different character and plots them out on a chart in two dimensions (potentially more). If microclots were big enough to block they should show up in a new part of the plot or scattered across regions - just not in a typical place for usual cells.

If the clots are slowing blood flow because they make it more viscous but are too small to block capillaries they would need to be present in high enough concentration to have more effect on viscosity than the usual cells. That is a tall order. About 45% of blood is made of normal red cells - making it much more viscous than plasma. To increase viscosity further noticeably you would need microclots in numbers sufficient to produce a pretty major fog of tiny particles on the Coulter plot. You would also expect to see a band of microclots sitting on top of the red cells when blood was left to settle or centrifuged.

So to produce any clinical effect you would expect the microclots to be barn door observable on routine clinical kit.

There is an interesting question as to whether these are in vitro artefacts that reflect a change on plasma soluble proteins rather than lumps. Both fibrinogen and amyloid proteins are standard acute phase reactants - which means they go up in inflammatory disease. The fibrinogen is present in enough quantity to cause a raised ESR and plasma viscosity. But we do not see those, or acute phase response proteins in ME/CFS or LC.

Some unusual protein might form amyloid lumps but there aren't that many options and such proteins should have been identifiable using standard immunochemistry.

So to me it is all very mysterious how on earth there can be anything there of clinical significance.

The muscle tissue that showed amyloid type fluorescence was not showing clots. The bright objects were 'vermiform' lines and dots and I am pretty certain they were nerves. Nerve endings are known to pick up that stain. It may be important that more staining was seen but I don't think it has anything to do with microclots.

 

I may be being stupid, but …

Is a reproducible difference in vitro being found in the presence of micro clots in the processed plasma between people with Long Covid or ME and healthy controls? If this is the case but it is looking like such micro clots are not an issue in vivo, does this mean that there is a real as yet unidentified anomaly in the patients’ blood though the micro clots themselves are not the cause of any pathology rather a downstream effect seen after processing samples.

 

I recall that an independent laboratory in the north of England, (independent of Pretorius et al), was going to try to replicate her work. I think the lead researcher was a haematologist. That was some months ago and not seen the results on here

My concern with this theory is there is no clear pathogenesis from having these fibrin-amyloid "micro clots" and the pathology that they cause. I think most is supposition. All I have read is somehow these particles are inflammatory and work on the endothelium or clotting cascades etc or on brain tissue and speculation this causes neuroinflammation.

But I have yet to see the necessary research to show pathogenesis, even in LC. I hoped we would have more information by now. Although Pretorius has done her study in South Africa, a few years ago, showing these "micro-clots" in people with ME. I think it would be useful to know how frequent microclots are in the general population. So a much larger study.

I don't think these microclots are blocking/impairing the microcirculation. Wouldn't it be pretty easy to attach some sort of radioactive particle to these microclots and do radiographic studies of them going around in the circulation? eg to see if they are impairing the microcirculation or activating something in the endothelium or in brain cells?

Could they test to see if there is some sort of dose response? i.e. the more micro-clots you have - the more severe the illness? but that doesn't really answer the question that is most needed - what are these fibrin amyloid particles actually doing?

I would be concerned that people with ME were being given anticoagulant treatment on the basis of their research. I am not sure how convincing the research is for LC either.

 

It's not yet published, but hopefully at least in preprint by the end of this year (Kräter, Scheibenbogen) but see the presentation here —

https://www.youtube.com/watch?v=Eds4MQk9ba0

This is unpublished.

 

Still in preprint, but see thread for Increased fibrinaloid microclot counts in platelet-poor plasma are associated with Long COVID (2024, Preprint: MedRxiv)

 

Thank you, I missed that one. It is good to see they have replicated her work but still unclear the clinical significance which may be made clearer in the preprint you mentioned on a dose response. Could it be a situation of ongoing active inflammatory response in some people with LC? (something I think is less clear in ME/CFS)

It appears from the Youtube video with Dr Martin Krater, that he believes that some people with LC are not able to clear these fibrin-amyloid micro clots from the circulation and that might be the basis of the pathology. The electron microscopy is interesting, I would like to see if research can tie the presence of these particles to specific symptoms and clinical signs of poor perfusion of tissues or increased viscosity of the blood etc.

 

So we are now really talking about non-covalent chemical interaction in solution. Biological chemistry gets complicated at these intermediate scales but an electrostatic effect without a 'lump' effect really boils down to a non covalent chemical effect. That is what fibrinogen and immunoglobulin normally do very well. They increase plasma viscosity (and ESR) by attracting red cells together. But these have not been reported as abnormal in ME/CFS or 'ME/CFS-type' LC. Autoantibodies could do it but they do not form amyloid aggregates.

 

Absolutely. This is the diplodocus in the room! Radiolabelling and injecting processed particles might be problematic and otherwise we don't seem to know what to radiolabel, but I think it is simpler than that. If these clots were causing vascular changes they would be clinically apparent. They aren't.

 

Maybe just to put this in perspective. Covid has been with us for five years now. We have seen about six papers on indirect evidence for thrombotic phenomena in LC. There are 1,450 papers on thrombotic phenomena with Covid vaccines, where clinical evidence is now well recognised.

 

One interesting possibility is that the causation is the other way around. Maybe in LC there is persistent endothelial activation because of some after effect of the spike protein interaction with ACE-R. Maybe that makes people feel generally fatigued. And secondarily there is a reactive shift in coagulation proteins, that do not actually contribute anything to the clinical problem.

 

Did they find these microclots in the blood of rodents that supposedly had ME?