The detection of functional growth factor (GF) receptors on subpopulations
of hemopoietic cells may provide a further dissection of immature cell
subsets. Since little information is available about coexpression of
different GF receptors at the level of single hemopoietic cells, we
studied the feasibility of simultaneous cell staining with a combination
of biotin- and digoxigenin-labeled GFs for flow cytometric detection of
functional receptors. Using this methodology, coexpression of Kit and
receptors for erythropoietin (EPO), interleukin 6 (IL-6), and GM-CSF on
hemopoietic cells was studied by triple-staining of rhesus monkey bone
marrow (BM) cells with labeled GFs and antibodies against other cell
surface markers. Most of the immature, CD34+2 cells were Kit+ but did not
display detectable levels of EPO-receptors (EPO-Rs) or GM-CSF-R.
Approximately 60% of these CD34+2/Kit+ cells coexpressed the IL-6-R,
demonstrating that immature cells are heterogeneous with respect to IL-6-R
expression. Maturation of monomyeloid progenitors, as demonstrated by
decreasing CD34 and increasing CD11b expression, is accompanied by a
decline of Kit and an increase in GM-CSF-R expression in such a way that
Kit+/GM-CSF-R+ cells are hardly detectable. IL-6-R expression is
maintained or even increased during monomyeloid differentiation. IL-6-R
and GM-CSF-R were not identified on most CD71+2 cells, which indicated
that these receptors are probably not expressed during erythroid
differentiation. Together with previous results, our data show that both
Kit and CD71 are upregulated with erythroid commitment of immature
progenitors. Upon further differentiation, Kit+/EPO-R-cells lose CD34 and
acquire EPO-R. Maturing erythroid cells eventually lose CD71 and Kit
expression but retain the EPO-R. In conclusion, this approach enables
further characterization of the specificity of GFs for different bone
marrow subpopulations. Apart from insight into the differentiation stages
on which individual GFs may act, information about receptor coexpression
may be used to identify individual cells that can respond to multiple GFs,
and allows for further characterization of the regulation of
lineage-specific differentiation