Circulating human b and plasma cells. age-associated changes in counts and detailed characterization of circulating normal CD138- and CD138 plasma cells

Generation of B and plasma cells involves several organs with a necessary cell trafficking between them. A detailed phenotypic characterization of four circulating B-cell subsets (immature-, naïve-, memory-B-lymphocytes and plasma cells) of 106 healthy adults was realized by multiparametric flow cytometry. We show that CD10, CD27 and CD38 is the minimal combination of subsetting markers allowing unequivocal identification of immature (CD10⁺CD27^-CD38⁺, 6±6 cells/mL), naïve (CD10^-CD27^-CD38^-, 125±90 cells/mL), memory B lymphocytes (CD10^-CD27⁺CD38^-, 58±42 cells/mL), and plasma cells (CD10^-CD27⁺⁺CD38⁺⁺, 2.1±2.1 cells/mL) within circulating CD19⁺ cells. From these four subsets, only memory B lymphocytes and plasma cells decreased with age, both in relative and absolute counts. Circulating plasma cells split into CD138^-(57±12%) and CD138⁺ (43±12%) cells, the latter displaying a more mature phenotypic profile: absence of surface immunoglobulin, lower CD45 positivity and higher amounts of cytoplasmic immunoglobulin, CD38 and CD27. Unlike B lymphocytes, both populations of plasma cells are KI-67⁺ and show weak CXCR4 expression.