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

It’s identified that excessive inflammation from an overactive immune response can spur the clots’ formation in severely sick sufferers (SN: 6/23/20). Now researchers are teasing out how. A few of that clotting could come from auto-antibodies that, as an alternative of recognizing a overseas invader, go after molecules that type cell membranes. That assault could immediate immune cells referred to as neutrophils to launch an internet 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 if you happen to do it within the bloodstream, it’s very triggering of thrombosis,” or clotting.

That could be what occurs in some COVID-19 patients, 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 explanation for demise, Kanthi says. And a few blood clots could type when the webs lure crimson blood cells and platelets, making a sticky clump that may clog blood vessels.   

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

Research have revealed that some auto-antibodies can interfere 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 common feature in severely sick COVID-19 sufferers.

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

These detrimental antibodies can even seem throughout bacterial or viral infections equivalent to strep throat or HIV. Nevertheless it’s tough to find out whether or not the antibodies result in blood clotting throughout an infection, Connors says, particularly as a result of some wholesome individuals may also have low ranges with out forming clots.

Severely sick 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 is likely to be inflicting neutrophils to launch traps that set off clotting.

Of 172 hospitalized COVID-19 sufferers included within the examine, greater than half had auto-antibodies that acknowledged one among three several types 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 battle. And when the researchers blended auto-antibodies taken from six COVID-19 sufferers with neutrophils grown in lab dishes, the neutrophils forged their nets. What’s extra, when the group injected affected person auto-antibodies into mice, the rodents shaped blood clots — hinting that clotting in individuals may very well 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 College of Medication who was not concerned within the work. Different inflammatory immune responses additionally set off clots, so auto-antibodies are most likely one piece of the puzzle. Of the individuals within the examine, for example, 11 sufferers developed blood clots, and solely half of them had the auto-antibodies.

Extra work must be executed to straight hyperlink the immune proteins to clotting in individuals with COVID-19, Connors says. However the examine does recommend one doable mechanism for the way the clots type.

Eradicating the problematic antibodies by way of a course of referred to as plasmapheresis, during which the liquid a part of blood is filtered, might assist critically sick COVID-19 sufferers who don’t reply to different therapies to cease clotting, Knight says. That plasma, nonetheless, would additionally comprise antibodies that acknowledge and assault the coronavirus. So docs may have to offer these sufferers lab-made immune proteins to battle the virus whether it is nonetheless replicating of their physique. 

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