Characterisation of the expression and function of the GM-CSF receptor α-chain in mice

The granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic cytokine able to regulate a variety of cell functions including differentiation of macrophages and granulocytes, dendritic cell development and the maintenance of homeostasis. It binds specifically to its receptor, which is composed of a cytokinespecific a-chain (GM-CSF receptor a-chain, GMR alpha) and a P-chain shared with the receptors for interleukin-3 and interleukin-5. In this report, we present a comprehensive study of GMRa in the mouse. We have found that the mouse GMRa is polymorphic and alternatively spliced. In the absence of specific antibodies, we generated a novel chimeric protein containing the Fc fragment of human IgG1 coupled to mouse GM-CSF, which was able to specifically bind to GMRa and induce proliferation of GMR alpha-transduced Ba/F3 cells. We used this reagent to perform the first detailed FACS study of the surface expression of mouse GMRa by leucocytes. Highest expression was found on monocytes and granulocytes, and variable expression on tissue macrophages. The GM-CSF receptor in mice is specifically expressed by myeloid cells and is useful for the detection of novel uncharacterised myeloid populations. The ability to detect GM-CSF receptor expression in experimental studies should greatly facilitate the analysis of its role in immune pathologies.