Blood clotting from severe COVID-19 caused by abnormal antibodies

Blood clotting and inflammation seen in very severe COVID-19 cases may be caused by abnormal antibodies, according to a new study

A new research paper has found that antibodies produced to protect against COVID-19 are triggering increased function of platelets and may be causing fatal blood clots.

Researchers took antibodies from people with severe Covid-19 infections and cloned them in a lab to study. The team found that the small sugars found on the surface of these antibodies were different to antibodies from healthy individuals, and when those cloned antibodies were introduced in a lab to blood cells taken from healthy donors, there was an observed increase in platelet activity.

Professor Jon Gibbins, Director of the Institute for Cardiovascular and Metabolic Research at the University of Reading said: “Until now, we have only had assumptions about why platelets involved in clotting were being activated during Covid-19 infection.

“One way to think of what is happens is that the immune response that is designed to protect you from the infection in some cases, particularly in severely ill patients, actually causes more damage. In this case, the antibodies that are produced to stop Covid-19 from spreading trigger infected cells to induce platelet activity which causes clotting even though there is no wound that needs healing.

“We are particularly excited because our studies of platelets in the laboratory establishes important mechanisms that explain how and why dangerous blood clots may occur in severely ill Covid-19 patients, and importantly, also provides clues as to how this may be prevented.”

Drugs trial

The team also found that it was possible to reduce or stop platelets from responding in this way by treating blood with active ingredients from different medications that are currently used to treat immune system problems.

A trial led by Imperial College London and Imperial College Healthcare NHS Trust – called MATIS – is already testing these drugs in clinical trials with patients across UK hospitals to see whether they will reduce serious blood clotting.

Co-author Nichola Cooper, reader at Imperial College London and consultant haematologist at Imperial College Healthcare NHS Trust, who also designed and leads the MATIS trial said: “Early on in the Covid-19 pandemic it was clear that the infection was causing an overwhelming immune response, including blood clotting, and that many of the more severe cases and deaths were related to this.

“Having been involved in early research around blood clotting related to inflammation, it occurred to me that the drugs we already use for other disorders could be easily accessible treatments for Covid-19. We are yet to see results from the MATIS trial so we do not yet know how these drugs will work in patients, but our hope is that we can both inhibit the inflammatory response and prevent severe disease and blood clots. It is exciting to see our collaboration with Reading backing our theory already and providing a solid scientific basis for clinical trials.”

The new paper has been published in the journal Blood.