Expression of interleukin 3 and granulocyte-macrophage colony-stimulating factor receptor common chain beta c, beta(IT) in normal haematopoiesis: lineage specificity and proliferation-independent induction

Interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM- CSF) and interleukin 5 (IL-5) exert their biological activities through int eraction with cell-surface receptors that consist of two subunits, a specif ic alpha subunit and a common beta transducing subunit (betac). We have eva luated the expression of betac on purified haematopoietic progenitor cells (HPCs) induced to unilineage differentiation/maturation through the erythro id (E), granulocytic (G), megakaryocytic (Mk) or monocytic (Mo) lineage. HP Cs displayed low betac expression, which increased during the initial stage s of HPC differentiation along the E, G, Mo or Mk lineages. At later stages of differentiation, betac chain expression increased in both G and Mo line ages, was expressed at low levels in the Mk lineage and declined to undetec table levels in the E lineage. Analysis of the full-length betac and intrac ytoplasmically truncated betac (beta (IT)) mRNAs showed that the former was predominant in the G and Mo lineages, whereas the latter was prevalent in the E and Mk lineages. The betac induction takes place even in the absence of cell cycling. Thus, incubation of HPCs with graded amounts of IL-3 showe d that the initial induction of betac expression is unrelated to cell proli feration. Furthermore, circulating monocytes and granulocytes exhibit a low level of betac expression that is greatly stimulated following incubation with either IL-3 or GM-CSF.