Following COVID-19, long-lasting immune activity in the airways might be the cause of persistent breathlessness.
According to a new study of 38 persons who had previously been hospitalized with severe COVID-19, this is a result of the findings.
These patients have a different immune system in their airways and signs of persistent lung damage, according to the reports. Despite the preliminary findings, this technique might improve over time.
Researchers argue that their findings must be confirmed in a larger study, but that recovery from COVID-19 might be accelerated by therapies that combat the immune system and reduce inflammation.
Dr James Harker, a joint author of the ImperialsNational Heart & Lung Institute, said: "Our study found that many months after SARS-CoV-2 infection, there were still abnormal immune cells in patients with persistent breathlessness. We also identified a protein signature in the lungs, indicating an ongoing inflammation to the airways.
Professor Pallav Shah, who is a co-author of the Imperials National Heart & Lung Institute, said that persistent breathlessness in our group of COVID-19 patients is being caused by a failure to turn off the immune response, which causes airway inflammation and injury. The next steps of our research will be to see if there are therapies that may reduce the immune activity and if they help to reduce the persistent breathlessness some patients experience.
By looking at markers in the blood, previous studies have investigated the causes of post-COVID-19 breathlessness, but the latest study examines directly at which immune cells are active in the lungs.
Lung scan discovery
The researchers looked at CT scans of the lungs and how well the lungs functioned, as well as looking at sample fluid from inside the lungs and blood samples to investigate the presence of nearly 500 proteins.
The total included 38 post-COVID-19 patients to compare against three to six months after they left the hospital, as well as 29 healthy volunteers (who had no underlying illnesses and had not had COVID-19).
The researchers examined how they found that there were more immune cells in the lungs of post-COVID-19 participants than in the healthy controls. However, there appeared to be no difference between the immune cells seen in the blood of the post-COVID-19 and the healthy participants.
Other research has found that the immediate response to COVID-19 involves an increase in many types of immune cells in the blood and in the lungs to combat the virus. For severe infections, like those seen in our study participants, there are also signs of inflammation.
"Toutefois, after three to six months, these signs in the blood appear to be back to normal, while those in the lungs take longer to resolve them. Our finding that the immune response in the blood does not appear to match the effectiveness of the lungs underscores the importance of monitoring airway immunity in order to better understand persistent respiratory problems after COVID-19.
For each post-COVID-19 patient, the immune cells in the lungs varied, but all had a higher level of immune cells resulting in cell death, epithelial damage, and tissue repair.
Different immune cells appeared to be in the lungs, resulting in increased number of cytotoxic T cells causing damage to the lung tissue and increased airway dysfunction, while having more B cells exhibited increased lung abnormalities in CT scans (such as scarring and physical changes).
Almost a year after their arrival at the hospital, a group of 17 post-COVID-19 participants were re-assessed, and 14 of them saw improvements in their symptoms and fewer lung abnormalities on CT scans. However, the number of immune cells present in their airways was significantly reduced compared to their earlier assessments. These findings suggest that these immune responses may improve over time.
Unclear impact for less severe disease
The authors conclude that their study consists of patients with severe COVID-19 illness (requiring hospitalization and ongoing monitoring), and that they are unclear if their conclusions will be applied to people with less severe disease. They were only able to study the participants lungs after COVID-19, and thus are unable to determine if any of the signs they discovered were present before infection.
The participants of the study noted that COVID-19 was found before vaccinations were available.