Scientists at King’s College London suggest that severe Covid infections can cause immune reactions that damage nerve cells in the brain, causing memory problems and confusion, and potentially raising the risk of long-term health issues. They found that a wayward immune response to the virus increased the death rate of neutrons and had a “profound” impact on regeneration in the hippocampus region of the brain, which is crucial for learning and memory.
While the findings are preliminary, they suggest Covid can trigger neurological problems in patients without the virus had to infect the brain itself. Professor of biological psychiatry at KCL’s Institute of Psychiatry, and senior author of the study, Carmine Pariante said, “These neurological symptoms are very concerning for patients and their families, and the hope is that our research can help identify which treatments would be most appropriate to lessen or prevent these symptoms.” The researchers analysed blood from 36 Covid patients admitted to Guy’s and St Thomas’ NHS Foundation Trust in London in the first wave of the pandemic. They found that levels of a protein called IL-6, which immune cells release as a rallying call for other immune cells, were more than 15 times higher than normal in infected individuals. However, a more dramatic rise in IL-6 was found in Covid patients with delirium.
The scientists then investigated how high levels of IL-6 might affect neurons in the hippocampus by exposing lab-grown nerve cells to the patient's blood. They found that blood from patients with delirium increased the normal death rate of neurons and reduced the generation of new brain cells. The damage caused is thought to drive delirium.
The harmful effects were traced back to a cascade of events where IL-6 triggers the release of two related immune proteins, called IL-12 and IL-13. Dr. Alessandra Borsini, the study’s first author, said the impact of the proteins on generating new brain cells was “profound”. “We believe these proteins are responsible for the delirium symptoms in acute Covid patients, and in general in long Covid patients experiencing neurological symptoms,” Borsini said. Measuring the levels of the immune proteins in patients could help personalise their treatment, she added.