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Fig. 2 | Cardiovascular Diabetology

Fig. 2

From: Proteomics of fibrin amyloid microclots in long COVID/post-acute sequelae of COVID-19 (PASC) shows many entrapped pro-inflammatory molecules that may also contribute to a failed fibrinolytic system

Fig. 2

Fluorescence microscopy showing platelets and microclots in individuals with long COVID and control samples. The first 2 columns show platelets in the haematocrit and the last column shows microclots in PPP. PPP were exposed to ThT, a fluorescent amyloid dye (final concentration: 0.005 mM) (Sigma-Aldrich, St. Louis, MO, USA) for 30 min at room temperature and protected from light. The same scoring system can be utilized to evaluate and interpret the fibrinaloid microclot load severity in PPP as published in our previous work [17]. We are aware that this isn’t a perfect system to aid as a quantitative score for qualitative data. Stage 1 would represent a minimal fibrinaloid microclot load as seen in healthy/control PPP, whereas Stage 4 represents a severe fibrinaloid microclot load. The fluorescent micrographs of representative samples of our long COVID cohort and control patients of haematocrit samples are stained with PAC-1 (green fluorescence) and CD62P-PE (purple fluorescence). The white areas represent areas where the two markers overlap, and the images were taken at 63 × magnification. The scoring system as described by Laubscher and Lourens et al. can be used to evaluate platelet activation and clumping in these fluorescence micrographs. In Stage 1 platelets are minimally activated and are seen as small and round with few pseudopodia (representative of healthy/control platelets). Severe platelet activation, or Stage 4 activation, is characterized by large, egg-shaped morphology with aggregations and is indicative of hyperactivated platelets. Similarly, platelet clumping can also be assessed with no clumping seen in healthy/control samples, which is classified as Stage 1 and severe clumping of platelets seen in Stage 4. Therefore, in our long COVID cohort, the fibrinaloid microclot load severity would fit with a severity of stage 2 to 3, and in some instances even a stage 4 (severe microclot load). Mild to moderate platelet activation (stage 2 to 3), as well as clumping are seen in micrographs D, E, G and H

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Cardiovascular Diabetology

ISSN: 1475-2840