Key points:
- Long COVID has distinct identifiable patterns of inflammation that can be detected in the blood.
- Certain groups of long COVID symptoms are associated with specific immune system proteins.
- These findings can guide the development of specific tests and treatments for the various types of long COVID to avoid a “one size fits all” approach.
A new study, published in Nature Immunology, examines patterns of inflammation detectable in the blood of people with long COVID. The findings can inform new targeted immune therapies for the treatment of long COVID.
Researchers compared 426 people who had been hospitalized for COVID-19 and were experiencing symptoms consistent with long COVID with 233 people who were also hospitalized for COVID but had fully recovered. They collected blood plasma samples and measured 368 proteins known to be involved in inflammation and immune system modulation.
The research team found that patients with long COVID showed a pattern of immune system activation that indicated inflammation of myeloid cells and activation of the complement system. They also obtained comprehensive information about the range of symptoms that patients experienced.
Certain groups of symptoms were associated with specific immune system proteins. For example, researchers found that gastrointestinal symptoms were linked to increased levels of a marker called SCG3, which is known to play a role in impaired communication between the gut and the brain. Overall, the team identified five overlapping subtypes of long COVID with different immune signatures. These subtypes highlight the different biological mechanisms of the disease and the underlying causes of various symptoms.
Researchers hope that their findings can influence treatment options, particularly those that target immune responses and inflammation. They point to IL-1 antagonists that are commonly used to treat rheumatoid arthritis and JAK inhibitors that treat some types of cancer as well as rheumatoid arthritis as potential therapeutics for long COVID.
“This work provides strong evidence that long COVID is caused by post-viral inflammation but shows layers of complexity,” said lead investigator Peter Openshaw, professor at Imperial College London. “We hope that our work opens the way to the development of specific tests and treatments for the various types of long COVID and believe that a ‘one size fits all’ approach to treatment may not work.”