Identification of early plasma cells in peripheral blood and their clinical significance

In the peripheral blood (PB) we detected so-called early plasma cells that might already be committed to entering the bone marrow (BM). By two-colour staining with FITC–anti-CD38 antibody, their intensity (CD38⁺⁺) of expression of CD38 antigen was between that of germinal centre (GC) B cells (low expression (CD38⁺)) and that of BM plasma cells (high expression (CD38⁺⁺⁺)), and their phenotype was CD38⁺⁺ CD19⁺ CD10⁻ CD20⁻ CD21⁺ CD24⁻ CD39⁺ CD5⁻ VLA-4⁺ VLA-5⁻ MPC-1⁻ without expression of surface membrane IgM (SmIgM). Morphological and immunological examination of the sorted cells confirmed that they were plasmacytoid cells with expression of cytoplasmic IgG (cIgG). Variations of these early plasma cells were examined in various diseases. In active systemic lupus erythematosus, bacterial septicaemia and liver cirrhosis, early plasma cell levels were significantly increased in PB, and after subsidence of such inflammation (inactive states) these cells returned to normal levels. In contrast, normal early plasma cells were significantly suppressed in myelomas, whilst normal or slightly increased numbers of early plasma cells was found in benign monoclonal gammopathy (BMG). In addition, the number of normal early plasma cells returned to a normal level in myeloma cases with complete responses. Therefore, early plasma cells were identified phenotypically, and an increase and decrease in these cells in PB may reflect mobilization and suppression, respectively, of activated B cells into BM plasma cells.