A sticky, net-like substance produced by an overactive immune system appears to contribute to increased blood clotting seen in the lungs of some patients diagnosed with COVID-19 and may provide a promising treatment target against lung injury, researchers are reporting.

Researchers have known for some time about a phenomenon called NETosis, in which infection-fighting white blood cells called neutrophils emit a sticky, web-like substance to trap invading viruses. While typically beneficial, the researchers showed in previous studies that overactive NETS, or Neutrophil Extracellular Traps, can exacerbate certain illnesses and clog blood vessels, leading to tissue damage.

In the current study, the researchers investigated the possibility that the net-like substance could be involved in deadly clotting association with COVID-19. The team examined plasma from 33 patients with COVID-19 along with tracheal secretions from their lungs and found that NET activity increased with disease severity. They found that patients on life support and those who had died from the disease had significantly more signs of NET activation than those who were not as sick or eventually recovered.  The NET response was lower in healthy people.

The researchers are currently evaluating a naturally occurring protein that is known to quiet the NET immune response as a possible treatment for clotting.  The current study, partly funded by NHLBI, appeared in the journal Blood.