Scientists have found the first evidence of overload of various inflammatory molecules, literally "trapped" inside insoluble microscopic blood clots (micro clots), that might be the cause of some of the lingering symptoms experienced by individuals with long COVID, new study has shown.

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A team from the Stellenbosch University (SU) in South Africa, analysing the blood samples from individuals with Long COVID unexpectedly found the micro clots and their molecular content. Their findings are published in the peer-reviewed journal Cardiovascular Diabetology.

"We found high levels of various inflammatory molecules trapped in micro clots present in the blood of individuals with Long COVID. Some of the trapped molecules contain clotting proteins such as fibrinogen, as well as alpha(2)-antiplasmin," explained Resia Pretorius, a researcher in the Department of Physiological Science at SU.

Alpha(2)-antiplasmin is a molecule that prevents the breakdown of blood clots, while fibrinogen is the main clotting protein. Under normal conditions, the body's plasmin-antiplasmin system maintains a fine balance between blood clotting (the process by which blood thickens and coagulate to prevent blood loss after an injury) and fibrinolysis (the process of breaking down the fibrin in the coagulated blood to prevent blood clots from forming).

With high levels of alpha(2)-antiplasmin in the blood of COVID-19 patients and individuals suffering from long COVID, the body's ability to break down the clots are significantly inhibited. The insolubility of the micro clots became apparent as researchers noted that the blood plasma samples from individuals with acute COVID and long COVID continued to deposit insoluble pellets at the bottom of the tubes after dilution (a process called trypsinisation).

The team made the finding using fluorescence microscopy and proteomics analysis, thereby solving yet another puzzle associated with the disease. "Of particular interest is the simultaneous presence of persistent anomalous micro clots and a pathological fibrinolytic system," they wrote in the research paper.

This implies that the plasmin and antiplasmin balance may be central to pathologies in long COVID. The findings provide further evidence that COVID, and even Long COVID, have significant cardiovascular and clotting pathologies. Further research is needed to understand clotting and fibrinolytic system function in individuals with lingering long COVID symptoms, the team said.