There is a lack of understanding as to why some people suffer from prolonged symptoms after COVID-19 infection. A new study from the Karolinska Institute in Sweden, Helmholtz Center Munich (HMGU) and the Technical University of Munich (TUM), both in Germany, now shows that a certain type of immune cell called macrophages shows altered inflammatory and metabolic expression several months later. mild COVID-19. The results are published in the journal Mucosal immunology.
“We can show that the macrophages from people with mild COVID-19 show an altered inflammatory and metabolic expression for three to five months after infection,” says Craig Wheelock, associate professor at the Department of Medical Biochemistry and Biophysics, Karolinska Institutet, and one of the study authors. “Although the majority of these people had no persistent symptoms, their immune system was more sensitive than that of their healthy counterparts.”
Long-term symptoms are relatively common after severe COVID-19 infection, but may also affect some people with a previous mild illness. More research is needed to understand the long-term immune disorders in patients who have recovered from the acute phase of the infection.
To investigate this aspect, the researchers in the current study analyzed blood samples from 68 people with a previous mild COVID-19 infection and a control group of 36 people who had not had COVID-19.
The researchers isolated the macrophages in the laboratory and stimulated them with peak protein, steroids and lipopolysaccharides (LPS), a molecule that triggers the immune system. The cells were then RNA sequenced to measure active genes. The researchers also measured the presence of eicosanoid signaling molecules, which are a fundamental feature of inflammation.
“It is not surprising to find a large number of eicosanoid molecules in people with COVID-19, as the disease causes inflammation, but it was surprising that they were still produced in large quantities several months after infection,” says Craig Wheelock.
The study also showed a higher concentration of leukotrienes, which are a type of pro-inflammatory molecule known to cause asthma.
“It is very striking that the concentration of leukotrienes remains elevated in macrophages in humans who have had mild COVID-19,” says study co-author Julia Esser-von Bieren, research group leader at Helmholtz Center Munich and the Technical University of Munich. Leukotrienes are important mediators of asthma, but they are also involved in the antiviral host defense against influenza. CoV-2 or other viruses. “
Blood samples were collected on two occasions, three to five months after SARS-CoV-2 infection and after 12 months. After three to five months, about 16 percent reported persistent mild symptoms, while the rest were asymptomatic. After 12 months, no persistent symptoms were reported and there was no longer any difference in inflammatory markers between those with previous COVID-19 infection and the healthy control group.
The researchers note that the post-COVID diagnosis was not specifically examined in the study, and as such, more research is needed to determine if these results can be directly linked to what is also known as long COVID.
“We would like to do a similar study where we involve both people with severe COVID-19 and people without COVID-19, but who have another type of respiratory disease, such as influenza,” says Esser-von Bieren. “We will then investigate whether what inflicts COVID-19 patients also inflicts on them with, for example, seasonal influenza.”
The study was funded by the Swedish Heart-Lung Foundation, the German Research Foundation (DFG) and the Helmholtz Association.
One of the authors has received support from Allergopharma, PLS Design and Zeller AG.