Although Frohman et al1 claim that B cells and plasma cells are present in the brain parenchyma in patients with multiple sclerosis (MS), Serafini et al2 found that both these cells were confined to the perivascular spaces. In only 1 area in a single patient were plasma cells detected in the brain parenchyma, and these were very sparse.
Crawford CL, Hardwicke PMD. Characterizing the Mechanisms and Progression in Multiple Sclerosis: Evidence and New Hypotheses for Future Directions. Arch Neurol. 2006;63(5):786-787. doi:10.1001/archneur.63.5.786-c