How COVID-19 could set off harmful blood clots

A few of COVID-19’s harmful blood clots could come from the immune system attacking a affected person’s physique somewhat than going after the virus, a brand new research suggests.

It’s recognized that extreme irritation from an overactive immune response can spur the clots’ formation in severely in poor health sufferers (SN: 6/23/20). Now researchers are teasing out how. A few of that clotting could come from auto-antibodies that, as a substitute of recognizing a overseas invader, go after molecules that kind cell membranes. That assault could immediate immune cells referred to as neutrophils to launch an online of genetic materials geared at trapping virus particles exterior of the cells.

“Presumably within the tissues, it is a technique to management infections,” says Jason Knight, a rheumatologist on the College of Michigan in Ann Arbor. “However should you do it within the bloodstream, it’s very triggering of thrombosis,” or clotting.

That could be what occurs in some COVID-19 sufferers, Knight, heart specialist Yogen Kanthi of the Nationwide Institutes of Well being in Bethesda, Md., and their colleagues report November 2 in Science Translational Medication. With COVID-19, blood clots within the lungs have been a big reason behind demise, Kanthi says. And a few blood clots could kind when the webs lure purple blood cells and platelets, making a sticky clump that may clog blood vessels.   

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“These are very intriguing findings,” says Jean Connors, a medical hematologist at Harvard Medical Faculty and Brigham and Girls’s Hospital in Boston who was not concerned within the work. “There was quite a lot of hypothesis about what the presence of [the auto-antibodies] means and whether or not they have any pathogenic function.”

Research have revealed that some auto-antibodies can intrude with the immune response to viruses (SN: 9/25/20). Some preliminary work additional means that auto-antibodies that bind to a wide range of targets within the host could also be a typical function in severely in poor health COVID-19 sufferers.

Auto-antibodies that acknowledge cell membrane molecules referred to as phospholipids may cause an autoimmune illness referred to as antiphospholipid syndrome, or APS. In folks with APS, the auto-antibodies can activate clot-forming cells, placing these sufferers at greater threat of blood clot formation.

These detrimental antibodies may seem throughout bacterial or viral infections resembling strep throat or HIV. But it surely’s troublesome to find out whether or not the antibodies result in blood clotting throughout an infection, Connors says, particularly as a result of some wholesome folks may additionally have low ranges with out forming clots.

Severely in poor health COVID-19 sufferers can have excessive ranges of neutrophils, and a few have phospholipid-binding antibodies of their blood. So Knight and his colleagues puzzled whether or not the antibodies could be inflicting neutrophils to launch traps that set off clotting.

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Of 172 hospitalized COVID-19 sufferers included within the research, greater than half had auto-antibodies that acknowledged one in every of three various kinds of host phospholipids. The presence of these immune proteins was linked to having excessive ranges of neutrophils within the blood and proteins that urged the neutrophils had joined the combat. And when the researchers blended auto-antibodies taken from six COVID-19 sufferers with neutrophils grown in lab dishes, the neutrophils solid their nets. What’s extra, when the crew injected affected person auto-antibodies into mice, the rodents shaped blood clots — hinting that clotting in folks could possibly be triggered by the immune proteins.

It’s unlikely that phospholipid auto-antibodies are the entire story, says Thomas Kickler, a hematologist at Johns Hopkins Faculty of Medication who was not concerned within the work. Different inflammatory immune responses additionally set off clots, so auto-antibodies are in all probability one piece of the puzzle. Of the folks within the research, as an example, 11 sufferers developed blood clots, and solely half of them had the auto-antibodies.

Extra work must be performed to immediately hyperlink the immune proteins to clotting in folks with COVID-19, Connors says. However the research does counsel one potential mechanism for the way the clots kind.

Eradicating the problematic antibodies via a course of referred to as plasmapheresis, wherein the liquid a part of blood is filtered, may assist critically in poor health COVID-19 sufferers who don’t reply to different therapies to cease clotting, Knight says. That plasma, nevertheless, would additionally include antibodies that acknowledge and assault the coronavirus. So medical doctors might have to provide these sufferers lab-made immune proteins to combat the virus whether it is nonetheless replicating of their physique. 

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