Summary: Fluorescence-activated cell sorting (FACS) analysis of B cell subtypes in 17 CSF samples from 15 patients with clinically-definite MS revealed that CD19+ B cells accounted for 2 to 11% (mean 5%) and CD138+ cells constituted 0 to 5% (mean 2%) of total CSF lymphocytes. Further stratification of CD138+ cells based on expression levels of CD19 showed that CD138+19+ plasma blasts constituted 89±2% (mean±SE) of the CD138+ cell population (Pb0.00001), with more mature plasma cells (CD138+19−) constituting the remaining 11±2%. Sequence analysis of immunoglobulin variable regions in single CD138+19+ and CD138+19− cells sorted from MS CSF identified many of the same clonal populations in both populations, indicating a continuum of clonally related plasma cell subtypes of which CD138+19+ plasma blasts are most abundant.
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