A central role for amyloid fibrin microclots in long COVID/PASC: origins and therapeutic implications
Kell DB, Laubscher GJ, Pretorius E
Biochemical Journal (2022)
The synthesis paper that frames amyloid fibrin microclots as a central mechanism of long COVID/PASC symptomatology — hypothesis-grade rather than validated mechanism, and the framework that underwrites the coagulation-focused therapeutic rationale that recurs in long-COVID communities.
This 2022 Biochemical Journal synthesis from Kell, Laubscher and Pretorius is the framework-articulating companion to the same group's 2021 Cardiovascular Diabetology characterisation paper and is the central reference cited in the long-COVID-and-peptides dossier for the broader "microclot hypothesis." Where the 2021 paper documented the observation — fibrinolysis-resistant amyloid-staining fibrin deposits in PASC plasma, with a distinctive protein cargo including α2-antiplasmin and serum amyloid A — this 2022 review proposes the consequential causal claim: that persistent fibrinaloid microclots block capillary perfusion across multiple organ systems and that this microcirculatory obstruction is a central mechanism underlying the long-COVID symptom complex including breathlessness, fatigue, post-exertional malaise, and cognitive dysfunction.
The paper synthesises three converging strands of evidence the authors had developed in the preceding decade. First, the broader fibrinaloid-microclot literature in non-COVID inflammatory conditions including type 2 diabetes, Parkinson's disease, and Alzheimer's disease, which had pre-figured the methodological approach and the amyloid-fibrin-deposit framework before SARS-CoV-2 emerged. Second, the SARS-CoV-2 spike-protein interaction biology in which the S1 spike subunit had been shown to bind fibrin(ogen) and induce structural changes consistent with amyloid fibre formation, providing a molecular-level mechanistic candidate for how SARS-CoV-2 infection would deposit fibrinaloid material. Third, the post-acute observation series including the 2021 PASC paper, in which microclots and a distinctive trapped-protein cargo were detected in plasma at long-COVID time points. The synthesis proposes that the fibrinaloid microclots, once formed and protected by their amyloid character from normal fibrinolysis (and locally inhibiting fibrinolysis by sequestering α2-antiplasmin), persistently obstruct capillaries and impair tissue oxygen and substrate exchange — yielding the multisystem fatigue, exercise intolerance, breathlessness, and cognitive dysfunction profile observed in PASC patients. The therapeutic implications section proposes that anticoagulation, fibrinolytic-supporting interventions, and approaches aimed at microclot removal warrant clinical investigation as candidate disease-modifying treatments. The framework has subsequently shaped one significant strand of the long-COVID treatment-investigation conversation including investigational triple-anticoagulant regimens and plasmapheresis-style approaches in the broader self-experimentation and clinic-protocol space.
This is a hypothesis-synthesis paper, not a primary characterisation of a validated mechanism. The honest framing — and the framing required by the underlying evidence — is that the microclot signal is empirically real and reproducible, but the causal claim that microclots drive PASC symptomatology is hypothesis-grade rather than established mechanism. The mechanistic claim that fibrinaloid microclots produce sufficient distributed capillary obstruction to account for the diversity and severity of long-COVID symptoms has not been independently established by quantitative histopathology, in-vivo microcirculatory imaging, or randomised-trial demonstration that microclot-targeted intervention produces symptom benefit. Subsequent independent groups have variously replicated the basic microclot-detection finding in PASC, in ME/CFS, in POTS, in some non-PASC POTS controls, and in other post-viral phenotypes — the Pretorius and Kell 2024 Research and Practice in Thrombosis and Haemostasis reassessment explicitly acknowledges that the microclot signal is detectable across multiple post-viral and POTS phenotypes, not only PASC, which complicates the specificity claim relative to long COVID as a discrete condition. The mechanism-to-treatment leap from "microclots are present" to "anticoagulation should treat long COVID" has not been tested in a randomised controlled trial as of 2026; observational protocols and self-experimentation in long-COVID patient communities have generated mixed reports without controlled comparison, and triple-anticoagulation regimens carry the same haemorrhagic-risk profile as in any other anticoagulation context. The authors include long-standing scientific and commercial involvement with the diagnostic-grade ThT-imaging characterisation of fibrinaloid microclots; that history is transparently disclosed in the paper but should be noted by readers as a structural prior in framing. Within this corpus, the appropriate reading is the one articulated in the long-COVID-and-peptides dossier: the microclot framework is real, its clinical significance is unsettled, and the leap from "microclot signal exists" to "peptide-stack X resolves it" is mechanism extrapolation on top of a contested mechanism.
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