The study, led by Daan van der Vliet, focused on brain tissue from patients with severe forms of MS. 

The researchers discovered large numbers of immune cells known as microglia that had accumulated fat droplets after absorbing damaged myelin, the protective layer surrounding nerve fibers in the brain and spinal cord.

Myelin is essential for efficient communication between nerve cells. In MS, the immune system attacks and damages this coating, leading to a range of neurological symptoms such as vision problems, difficulty walking, and in advanced cases, paralysis. 

However, the disease does not progress in the same way for all patients, and scientists have long sought to understand the reasons behind these differences.

In affected brain regions, the researchers observed that microglia became overloaded with fat, giving them a “foamy” appearance. 

These cells normally help maintain brain health by clearing away damaged material and supporting repair. However, when overwhelmed by large amounts of myelin debris, they appear to change behavior.

According to the study, patients with a higher presence of these “foamy microglia” were more likely to experience a severe and rapidly progressing form of MS. This suggests that the buildup of fat within these immune cells may be linked to worsening disease outcomes.

Further analysis showed that brain lesions containing foamy microglia had distinct molecular characteristics compared to those without them.

 These areas were enriched with specific types of fats associated with ongoing inflammatory activity, indicating that the process may contribute to sustained inflammation in the brain.

Researchers explain that while microglia are initially intended to protect the brain by clearing damaged tissue, they may become dysfunctional when overloaded.

Instead of supporting repair, these cells may lose their effectiveness and contribute to continued inflammation and tissue damage.

The findings suggest that MS progression may not be driven by inflammation alone, but also by a breakdown in the brain’s natural repair system. When this system becomes overwhelmed, it may unintentionally contribute to further damage.

Scientists say the discovery could open new research directions, including the development of biomarkers that help predict disease progression and potential strategies to prevent immune cells from becoming overloaded.

While further studies are needed, the research provides important new insight into the complex mechanisms behind multiple sclerosis and how the brain’s own immune cells may play a dual role in both repair and damage.