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Thursday, February 17, 2022


After studying blood samples from 244 patients admitted for COVID-19, a group of researchers, including those working at the National Institutes of Health, identified “sluggish antibodies” that correlate with serious illness and may help explain mechanisms associated with severe blood clots. The researchers found circulating antiphospholipid antibodies, which may be more common in people with autoimmune disorders, such as lupus. These “autoantibodies”Which targets a person’s own organs and systems, can also be activated in response to viral infections and activate other immune responses.

Researchers compared the blood samples with those from healthy controls and found that the COVID-19 samples contained higher levels of the antibody IgG, which works with other immune cells, such as IgM, to respond to immune threats. Higher levels of IgG were also associated with the severity of COVID-19 disease, such as in patients in need of respiratory assistance. The researchers observed similar patterns, but to a lesser extent, after analyzing blood samples from 100 patients admitted for sepsis, which can leave the body in inflammatory shock after a bacterial or viral infection.

IgG helps to bridge the gap between innate and adaptive immune responses – a process that helps the body recognize, respond to and remember dangers. In normal cases, these functions help protect the body from disease and infection. However, in some cases, this reaction may become hyper-extensive or altered and exacerbate disease. A unique finding from this study is that when researchers removed IgG from the COVID-19 blood samples, the molecular indicators of “blood vessel adhesion” decreased. When they added the same IgG antibodies to the control samples, they saw a vascular inflammatory reaction that could lead to coagulation.

Since each organ has blood vessels in it, circulating factors that lead to the “stickiness” of healthy blood vessels during COVID-19 can help explain why the virus can affect many organs, including the heart, lungs, and brain. One query in this study was to evaluate “upstream” factors involved in severe blood clots and inflammation in people with severe COVID-19 disease.

The researchers note that future studies may explore the potential benefits of screening patients with COVID-19 or other forms of critical illness for antiphospholipids and other autoantibodies and at previous points of infection. This can help identify patients at risk for extreme blood clots, vascular inflammation and respiratory failure. Similar studies could then assess the potential benefits of giving these patients treatments to protect blood vessels or fine-tune the immune system.


Yogen Kanthi, MD, a co-corresponding author, is available to discuss this research. Dr. Kanthi is a cardiologist, Clinical Lasker Research Scholar, and leader Laboratory for vascular thrombosis and inflammation at the National Heart, Lung, and Blood Institute. He is also an Assistant Professor of Cardiovascular Medicine at the University of Michigan, Ann Arbor.


Endothelial cell activating antibodies in COVID-19. Arthritis and rheumatology2022. DOI:

About the National Heart, Lung, and Blood Institute (NHLBI): NHLBI is the global leader in conducting and supporting research into heart, lung and blood diseases and sleep disorders that promotes scientific knowledge, improves public health and saves lives. For more information, visit

About the National Institutes of Health (NIH):The NIH, the nation’s medical research agency, includes 27 institutes and centers and is part of the U.S. Department of Health and Human Services. The NIH is the primary federal agency that conducts and supports basic, clinical, and translational medical research and investigates the causes, treatments, and cures for both common and rare diseases. For more information on the NIH and its programs, visit

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