MKI67 and myeloid sarcoma: The identification of CD19 + CD38hiCD77 + Ki67 + Bcl2− centroblasts in the CSF but not the peripheral blood of MS patients suggests that a compartmental humoral immune response in the MS CNS recapitulates all stages of B cell differentiation and may create a self-sufficient CNS response that is independent of the immune activity in the periphery (13).