In the brains of people with long-term multiple sclerosis, inflammatory cells are not entering the brain via the bloodstream anymore. A new study suggests the cells arise from local memory cells in the brain instead. 

Brain tissue donated by MS patients that passed away was examined at the Netherlands Brain Bank. In this tissue, researchers at the Netherlands Institute for Neuroscience found activated T cells inside of the inflammatory lesion centers. These cells had characteristics of tissue-resident memory T cells. This kind of T cell remains in tissues after viral infections and offers long-term local protection to new infections.

These new findings support the idea that during the late phase of MS, the disease is happening entirely inside the brain. In this case, white blood cells on the outside of the brain do not influence the disease any more. Researchers said the data provide insight into the disappointing effects of current treatments during later stages of MS. By mapping the behavior of the T cells, researchers can start thinking of ways to slow down the disease process in patients with advanced MS.

The findings were published in the scientific journal Brain.