IL-3Rβ Background Information The human IL-3, IL-5 and GM-CSF receptors are each composed of both unique a subunits and a common ∫ subunit. The a subunits are low affinity ligand binding proteins while the ∫ subunits do not themselves bind ligand, but are required for high affinity binding by the a subunits. In contrast, the mouse IL-3 receptor has two distinct ∫ subunits, one that functions only in IL-3 mediated cell signaling and a second that is shared with IL-5 and GM-CSF. The murine ∫-subunits are 91% homologous at the amino acid level but only 56% homologous to the human ∫ subunit. Although neither the murine nor the human ∫ subunit contains tyrosine kinase domains, both activate tyrosine phosphorylation mediated signaling pathways.
