Why Covid Patients Need Prolonged Ventilation

London: The majority of patients with severe Covid-19 develop unusually pronounced scarring of the lungs, due to a misguided immune response, study finds.

A team of researchers led by Charite – Universitatsmediz in Berlin, in the journal Cell, reported that macrophages – immune cells that engulf and digest foreign substances – play a central role.

In patients with severe Covid-19, the damage to the lungs is so severe that the body can no longer absorb enough oxygen from the air – a condition known as acute respiratory distress syndrome (ARDS).

“At the very least, SARS-CoV-2 is a potential trigger for an erroneous macrophage response,” explained Professor Matthias Selbach, of the Max DelbrAck Center for Molecular Medicine (MDC).

“Rather than replicating itself inside immune cells, the virus seems to reprogram them,” he added.

Researchers looked at a number of potential causes of this prolonged lung failure, including a particular type of ARDS, which causes scarring in the lungs leading to thickening and stiffness of the tissues.

This type of tissue remodeling (called fibrosis) had been observed in some patients relatively early in the pandemic.

As part of their research, the team used a number of microscopic imaging techniques to study lung tissue from patients who died from Covid-19.

“Almost all of the affected patients presented with extensive tissue damage. The majority of the alveoli had been destroyed and the alveolar walls showed significant thickening. We also found ubiquitous deposits of collagen, the main component of scar tissue. All of this is characteristic of severe fibrosis, ”said Professor Dr Peter Boor, Head of the Institute of Pathology at RWTH Aachen University Medical Center.

The reason for this phenomenon was initially unclear.

In patients with Covid-19, respiratory failure usually does not develop until two to three weeks after the onset of symptoms, when viral loads have started to drop.

“This suggests that lung failure is not caused by uncontrolled viral replication, but by secondary host responses, including those involving the immune system,” explained

Teacher. Dr. Leif Erik Sander from the Department of Infectious Diseases and Respiratory Medicine at Charite.

The researchers therefore analyzed the composition and characteristics of immune cells taken from bronchio-alveolar lavage samples and lung tissue from severe and deceased Covid patients.

They found that the pronounced build-up of macrophages is one of the main characteristics of Covid-19 patients who develop respiratory failure.

Using cell cultures, the researchers found that SARS-CoV-2 exerts an effect on macrophages which can, in turn, speed up the process of fibrosis.


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