“We can show that the macrophages from people with mild COVID-19 exhibit an altered inflammatory and metabolic expression for three to five months post-infection,” says Craig Wheelock, docent at the Department of Medical Biochemistry and Biophysics, Karolinska Institutet, and one of the study’s authors. “Even though the majority of these people did not have any 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 individuals with previous mild disease. More research is needed to understand the long-term immune aberrations in patients who have recovered from the acute phase of the infection.
To examine this aspect, the researchers in the current study analysed blood samples from 68 people with 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 spike 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.
Unexpected discovery
“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 being produced in high quantities several months after the infection,” Craig Wheelock says.
The study also showed a higher concentration of leukotrienes, which are a type of pro-inflammatory molecules known for causing asthma.