B-cells from MS patients secrete something toxic, maybe exosomes.
Most evidence from pathological studies suggests that demyelination and neurodegeneration in MS is driven by the inflammatory cells, but that these processes are not directly induced by cellular contacts. In addition, plaque like primary demyelination is a specific feature of MS, not seen in other inflammatory conditions of the brain and spinal cord with the exception of diseases with viral infection of oligodendrocytes.
Evidence from expanding cortical lesions and slowly expanding white matter lesions suggest that demyelination and neurodegeneration is driven by an MS specific soluble factor, produced by inflammatory cells, which induces tissue damage either directly or indirectly through microglia activation, and that this soluble factor may be produced by B-cells from MS patients, but not from controls.
To identify the molecular nature of this soluble factor will be instrumental for our understanding of MS pathogenesis.
UPDATE: Some reports point to exosomes as the toxic factor (https://onlinelibrary.wiley.com/doi/ful ... cen3.12474)