The effect of IL-3 on the B lymphoid potential of human hemopoietic stem ce
lls is controversial. Murine studies suggest that B cell differentiation fr
om uncommitted progenitors is completely prevented after short-term exposur
e to IL-3, We studied B lymphopoiesis after IL-3 stimulation of uncommitted
human CD34(+)CD38(-) cells, using the stromal cell line S17 to assay the B
lymphoid potential of stimulated cells. In contrast to the murine studies,
production of CD19(+) B cells from human CD31(+) CD38(-) cells was signifi
cantly increased by a 3-day exposure to IL-3 (p < 0.001), IL-3, however, di
d not increase B lymphopoiesis from more mature progenitors (CD34(+)CD38(+)
cells) or from committed CD33(-)CD19(+) B cells, B cell production was inc
reased whether CD34(-)CD38(-) cells were stimulated with IL-3 during cocult
ivation on S17 stroma, on fibronectin, or in suspension. IL-3R<alpha> expre
ssion was studied in CD34(+) populations by RT-PCR and FAGS. High IL-3R alp
ha protein expression was largely restricted to myeloid progenitors. CD34()CD38(-) cells had low to undetectable levels of IL-3R alpha by FAGS. IL-3-
responsive B lymphopoiesis was specifically found in CD34(+) cells with low
or undetectable IL-3R alpha protein expression. IL-3 acted directly on pro
genitor cells; single cell analysis showed that short-term exposure of CD34
(+)CD38(-) cells to IL-3 increased the subsequent cloning efficiency of B l
ymphoid and B lymphomyeloid progenitors. We conclude that short-term exposu
re to IL-3 significantly increases human B cell production by inducing prol
iferation and/or maintaining the survival of primitive human progenitors wi
th B lymphoid potential.