Expression of CD19 and CD20 during human B-cell development. B
cells emerge from hematopoietic stem cells (HSC) and acquire
maturity in the bone marrow (BM). During this process, CD19
expression starts at the stage of late pro-B cells and precedes
that of CD20, starting in immature B cells. CD19 and CD20
expression is maintained during B-cell differentiation and
activation in the periphery, while activation and
differentiation into memory B cells may fine-tune expression
levels. During activation of B cells in lymphoid organs - such
as the spleen and tonsil, resulting in their differentiation
into plasmablasts and finally plasma cells - CD20 expression is
downregulated and subsequently lost. At the same time, CD19
expression is partially downregulated but not extinguished.
Being released into circulation, only few plasmablasts express
low amounts of CD20, while most have lost CD20 expression but
express CD19. After successful immigration into deposits in the
BM or the lamina propria (LP), all plasma cells lac