Epigenetic Memory in Macrophages Post-COVID
Recent research shows that macrophages key immune cells develop a type of “memory” after COVID-19. This memory enhances their ability to respond to unrelated viruses. Immunological memory was previously thought to be limited to adaptive immune cells, but new findings challenge this idea. Interestingly, what macrophages remember is not specific to any single virus.
Immune Response Process
When a virus enters the body, cytokines signal macrophages to attack and eliminate threats. This initial response is general. Later, adaptive immune cells like T cells specifically target the virus, tailoring their response and retaining a memory for future encounters. Understanding this innate immune memory could lead to new therapies that protect against multiple viruses.
Studies over the last two decades have shown that innate immune responses can create lasting cellular memories. For instance, people vaccinated with the Bacillus Calmette-Guérin (BCG) vaccine, which protects against tuberculosis, exhibited lasting innate immune memory that helped defend against other infections.
Genetic Changes Post-Infection
Researchers led by Lercher explored the long-term effects of SARS-CoV-2 in the lungs. They found that alveolar macrophages developed a new epigenetic profile after infection. Specifically, the chromatin around antiviral genes became more accessible, making them ready for action post-recovery.
These findings also applied to humans. Analyzing blood samples from people who recovered from mild COVID revealed similar epigenetic changes in monocytes, which are precursor cells to macrophages.
This epigenetic reprogramming results in memory of past infections and alters future immune responses.
Improved Defense Mechanism
Macrophages in the lungs of mice that recovered from COVID showed improved antiviral memory. They were better equipped to combat new viral threats, like influenza A, exhibiting fewer symptoms and lower mortality rates compared to naïve mice. Researchers confirmed these findings by exposing mice to a synthetic RNA virus, observing similar memory responses.
Future Research Goals
The next step is to identify the key factors that establish this innate immune memory. “Ideally, we’d pinpoint one or a few factors that encourage memory formation in macrophages and other innate cells,” says Rice. This could lead to therapies offering broad protection against various viruses.
Such an approach could be crucial during a pandemic. Lercher notes that having a therapy to boost general antiviral immunity could be valuable if a new pathogen emerges. While this goal is still distant and requires more research, it holds promise for the future.
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