Why does the long COVID last so long, leaving long haulers with symptoms that persist for months after the initial infection?
New evidence suggests that the lasting imprint of COVID-19 could be due to the virus changing people’s blood dramatically – leading to lasting changes in blood cells that are still evident months after infection is diagnosed.
“We were able to detect clear and lasting changes in cells – both during acute infection and even after,” says biophysicist Jochen Guck of the Max Planck Institute for Light Science in Germany.
In a new study, Guck and other researchers analyzed the blood of patients using an in-house developed system called real-time strain cytometry (RT-DC), capable of quickly analyzing hundreds of blood cells per second, to detect if they are exhibiting abnormal changes in their size and structure.
The technology is relatively new, but it could do a lot to explore what remains a major unknown in COVID-19 science: how the coronavirus can impact blood at the cellular level.
“Although the pathology is not yet fully understood, the hyper-inflammatory response and coagulation disorders leading to congestion of microvessels are considered to be the main factors in the ever-increasing number of deaths,” write the researchers, led by the first author Markéta Kubánková, in their article. .
“So far, physical changes in blood cells have not been considered to play a role in COVID-19-related vascular occlusion and organ damage.”
In the study, researchers analyzed the blood of 55 people: 17 patients with severe COVID-19 (half of whom sadly died later), 14 recovered patients, and 24 healthy volunteers who showed no signs of having had the disease.
In total, more than 4 million blood cells taken from these people were passed through the RT-DC system, analyzed under a microscope as they passed through a narrow channel in the device.
The results showed that red blood cells (erythrocytes) in COVID-19 patients varied more in size than those in healthy people and showed signs of stiffness in their physical structure, exhibiting less deformability, which could affect their ability. to deliver oxygen throughout the body.
“The physical properties of erythrocytes are crucial for microcirculatory flow and, as such, these changes could impair circulation and promote hypoxemia,” the researchers explain.
“The effect may persist in COVID-19 patients long after the infection is no longer active; we found that in recovered patients, the alterations in phenotype were not as significant, but still present.”
In contrast, the researchers found that a form of white blood cells (leukocytes) called lymphocytes exhibited reduced stiffness in COVID-19 patients, while other white blood cells, called monocytes, were significantly larger than in blood cells. a group of witnesses.
Meanwhile, neutrophils – another type of white blood cell – have shown many changes in COVID-19 patients, seen in higher volume, with greater strain.
Interestingly, neutrophils have a particularly short lifespan (only around a day), but changes in neutrophils in COVID-19 patients could still be seen months after infection, a result Kubánková describes as “totally unexpected” – and even more evidence of COVID-19 infection likely leaving a lasting influence on the immune system.
“While some of these changes returned to normal values after hospitalization, others persisted for months after discharge from hospital, testifying to the long-term imprint of COVID-19 on the body.” , write the researchers.
“We hypothesize that the observed changes could occur due to alterations in the cytoskeleton of immune cells. The mechanical properties of cells may be directly related to the cytoskeleton, an important supporting structure that also determines cell function.”
It remains to be seen how these changes in blood cells can ultimately be triggered by a viral infection, and it is not yet completely clear how the alterations in the cells lead to symptoms of COVID-19, and sometimes to death.
For now, this is just further proof of how deeply this virus invades our bodies – and why it sometimes doesn’t let people go.
“The persistent alterations in erythrocytes and neutrophils could be linked to long-term symptoms of the cured patients, of whom 70 percent described chronic headaches or neurological symptoms, 54 percent had impaired concentration and 62 percent circulatory problems like cold sweats and tachycardia, ”the authors explain. write.
“We hypothesize that persistent changes in the physical phenotypes of blood cells may contribute to the long-term impaired circulation and oxygen supply associated with COVID-19.”
The results are reported in Biophysical Journal.