Detection of Ectopic B‐cell Follicles with Germinal Centers in the Meninges of Patients with Secondary Progressive Multiple Sclerosis

Multiple sclerosis (MS) is characterized by synthesis of oligoclonal immunoglobulins and the presence of B‐cell clonal expansions in the central nervous system (CNS). Because ectopic lymphoid tissue generated at sites of chronic inflammation is thought to be important in sustaining immunopathological processes, we have investigated whether structures resembling lymphoid follicles could be identified in the CNS of MS patients. Sections from post‐mortem MS brains and spinal cords were screened using immunohistochemistry for the presence of CD20+ B‐cells, CD3+ T‐cells, CD 138+ plasma cells and CD21+, CD35+ follicular dendritic cells, and for the expression of lymphoid chemokines (CXCL13, CCL21) and peripheral node addressin (PNAd). Lymphoid follicle‐like structures containing B‐cells, T‐cells and plasma cells, and a network of follicular dendritic cells producing CXCL13 were observed in the cerebral meninges of 2 out of 3 patients with secondary progressive MS, but not in relapsing remitting and primary progressive MS. We also show that proliferating B‐cells are present in intrameningeal follicles, a finding which is suggestive of germinal center formation. No follicle‐like structures were detected in parenchymal lesions. The formation of ectopic lymphoid follicles in the meninges of patients with MS could represent a critical step in maintaining humoral autoimmunity and in disease exacerbation.