MS Immune Networks: Acute and Chronic Inflammation Beyond Single Cells

"MS Immune Networks: Acute and Chronic Inflammation Beyond Single Cells" takes up how immune activity drives MS both from outside and within the central nervous system.

Dr. Singer explains that two processes run in parallel in MS. Early in the disease, perivascular and perivenular cuffs of lymphocytes and monocytes move from the periphery into the central nervous system and create the acute lesion. As that lesion resolves, roughly 20% of the cells remain, including CD8 cells, leaving chronic inflammation behind.

In the chronic phase, Dr. Singer describes ongoing compartmentalized inflammation inside the central nervous system. He highlights chronic active lesions with microglial rims and meningeal inflammation, where soluble factors drive demyelination in the cortex. Microglial activation is also widespread in normal-appearing white matter. Axonal injury and Wallerian degeneration mean that this tissue is not truly normal, and remyelination fails as patients age. Inflammation arriving from the periphery is only part of the picture.

Dr. Greenberg notes that explanations to patients were easier when understanding was incomplete, and he asks Dr. Krieger how to integrate these distinct entities. Dr. Krieger observes that clinicians tend to define the disease by whatever they can see. Lesions were once viewed as static, yet they can expand at the rim in ways conventional MRI does not capture.

Dr. Krieger adds that B-cell depleting therapies have defined the past decade because they are so effective. That success may have encouraged a one-cell-at-a-time view of the disease. He argues instead that MS is a network problem, involving compartmentalized immune processes in the central nervous system and immune influx across the blood-brain barrier. Meningeal aggregates of lymphocytes and B cells cannot be seen on conventional MRI but may still potentiate disease. He calls for targeted strategies that interrupt these networks, perhaps without depleting cells at all, to address both relapsing and progressive pathology.

Our next episode, "When MS Progression Begins: Early Injury and Relapsing vs Progressive Biology," turns to Dr. Rosenthal and Dr. Singer on when irreversible injury begins.