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Feb. 17 (UPI) -- "Rogue antibodies" linked to severe COVID-19 may be behind the blood clots some people develop after getting infected with the virus, a study published Thursday by the journal Arthritis and Rheumatology found. Patients with severe COVID-19 who had life-threatening blood clots caused by the virus have higher levels of what are called antiphospholid antibodies, such as immunoglobulin G, in their blood than those who did not experience clotting, the data showed.
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These antibodies are common among people with autoimmune disorders such as lupus, though they can also be activated in response to viral infections and activate other immune responses, researchers from the National Heart, Lung and Blood Institute said.
Antibodies are proteins produced by the immune system to fight off viruses.
Severe "COVID-19 is not only a lung disease, but actually significantly affects the blood flow and blood clotting systems," researcher Resia Pretorius wrote in an op-ed published in the Guardian in January.
Though she was not part of the National Heart, Lung and Blood Institute study, Pretorius and her colleagues have found in their research "significant microclot formation in the blood of both acute COVID-19 and long-COVID patients."
The presence of these microclots, or small blood clots, could be used to identify people at risk for developing long COVID, said Pretorius, a professor of physiological sciences at Stellenbosch University in South Africa.
Long COVID, or long-haul COVID, has been described as virus-related symptoms that persist for months, long after the infected person has recovered from their initial illness.
It has been compared with chronic fatigue syndrome, though sufferers experience damage to the heart and other organs.
Up to half of people infected with the virus develop long-term symptoms, research suggests, while as many as one in five people with COVID-19 develop blood clots, according to researchers at the University of California-San Diego.
Blood clots have also been cited as a rare side effect of some of the available vaccines against COVID-19.
For the National Heart, Lung and Blood Institute study, researchers led by Dr. Yogen Kanthi, an assistant professor of cardiovascular medicine at the University of Michigan in Ann Arbor, analyzed blood samples collected from 244 patients hospitalized for COVID-19.
They compared the blood samples from infected patients to those from healthy controls and found the COVID-19 samples contained higher levels of the antiphospholid antibody immunoglobulin G, which works with other immune cells to respond to viruses, they said.
Patients with higher levels of immunoglobulin G tended to have more severe illness from COVID-19, and often needed breathing assistance, the researchers said.
Immunoglobulin G helps the body's immune system recognize, respond to and remember dangerous pathogens such as viruses, according to the researchers.
Normally, these characteristics help protect the body from illness and infection, they said.
However, in some cases, this response can become hyperextended or altered and worsen illness, the researchers said.
When they removed immunoglobulin G from the collected blood samples in patients with COVID-19, indicators of "blood vessel stickiness" fall, they said.
Conversely, when they added these same immunoglobulin G antibodies to the blood samples collected from the healthy controls, they saw a blood vessel inflammatory response that can lead to clotting.
Because every organ has blood vessels in it, circulating factors that lead to the "stickiness" of healthy blood vessels in COVID-19 may help explain why the virus can affect many organs, including the heart, lungs and brain, the researchers said.
Based on these findings, it is possible that patients with COVID-19 could be screened antiphospholid antibodies earlier after infection to identify those at risk for blood clots, Kanthi and his colleagues said.
