Long COVID, also known as post-acute sequelae SARS-CoV-2 (PASC), is a condition that affects people who have recovered from COVID-19 and experience symptoms for an extended period of time. With over 65 million people worldwide estimated to live with this debilitating condition, researchers are desperate to understand the underlying biology driving it. The aim is to identify effective treatments and tests that can help alleviate symptoms and improve the quality of life.
Researchers at the US National Institute of Health conducted extensive testing on 12 people with long COVID and compared the results against a group of healthy volunteers who had not contracted COVID. The researchers looked for abnormalities in blood samples, cerebrospinal fluid, and MRI scans and ran a series of tests to detect autonomic nervous system dysfunction.
Immune System Abnormalities
One of the most significant disparities between people with long COVID and healthy volunteers was the immune cell count. Participants with long COVID had decreased numbers of immune cells called memory T cells, which usually persist for an extended period after infections, retaining the ability to recognize a specific threat and call the rest of the immune system rapidly to arms upon re-exposure. COVID long haulers had increased numbers of immune cells called B cells, antibody-secreting B cells, and activated natural killer cells, which detect and destroy damaged cells. People with long COVID also had an increase in immune checkpoint molecules like TIGIT and PD-L1 on immune cells, “suggesting the possibility of immune exhaustion.”
Dysfunction in the Autonomic Nervous System
Researchers also examined dysfunction in the autonomic nervous system, which controls heart rate, blood pressure, and breathing. People with long COVID often report a racing heart, dizziness, and feeling faint when moving from a sitting to a standing position, known as postural orthostatic tachycardia syndrome (POTS). The researchers found that people with long COVID were less able to control their heart rate and blood pressure when these physiological pressures were applied. Additionally, the skin temperature was lower in people with long COVID throughout the tilt-table test, suggesting vasoconstriction, where the blood vessels constrict and decrease blood flow to the skin.
Implications for Treatment
While more research is needed to make head or tail of all this, the research does suggest that immunotherapies could be explored as a treatment for long COVID in clinical trials. The preliminary findings call for further investigation and for evaluation of potential immunomodulatory agents in an effort to decrease the huge public health burden of this syndrome.
Long COVID is a debilitating condition that affects millions of people worldwide. The underlying biology driving the condition is not yet fully understood, but research suggests immune system abnormalities and dysfunction in the autonomic nervous system are contributing factors. The findings also suggest that immunotherapies could be explored as a treatment for long COVID in clinical trials. Further research is needed to fully understand the condition and to identify effective treatments and tests that can alleviate symptoms and improve the quality of life for those living with it.
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