The alpha subunit of the GM-CSF receptor binds GM-CSF with relatively low affinity. Binding of this dimer to the common beta subunit (Bc) confers high affinity binding. Recent models of receptor activation suggest a sequential activation that is initiated by the low-affinity interaction of GM-CSF with the alpha chain to form a binary complex. This binary complex is then able to bind preformed Bc dimers generating a 2:2:2 hexameric complex (Hansen et al. 2008).