Normal and malignant human plasma cells: proliferation, differentiation, and expansions in relation to CD45 expression.

In this study, we have evaluated the proliferation and the phenotype of human plasma cells of different origins, i.e., from tonsil, peripheral blood, bone marrow as well as plasma cells generated in vitro from memory B cells. We have demonstrated that plasma cells from tonsil, peripheral blood, as well as those generated in vitro, were highly proliferating and presented a homogeneous CD45bright phenotype. In contrast, bone marrow plasma cells were heterogeneous for CD45 expression but their proliferation was restricted to the CD45bright compartment. Subsequently, their CD45 expression decreased with proliferation arrest and final maturation. We also studied the proliferation of abnormal plasma cells, i.e., peripheral blood reactive plasmacytoses and multiple myeloma (MM). All reactive plasmacytoses turned out to be homogeneous expansions of CD45bright plasma cells with unusually high labeling index. In contrast, CD45 expression was heterogeneous in MM as in normal bone marrow. However, a minor CD45bright population was also always the most proliferating one as opposed to a major population of less or non-proliferating myeloma cells characterized by a weaker or a lack of CD45 expression. In conclusion, proliferation is linked to plasma-cell generation and a CD45bright phenotype is the hallmark of the most proliferating normal, reactive as well as malignant plasma cells.