The PathHunter Sargramostim Bioassay is an application of the DiscoverX Dimerization Assay platform, which can be used to detect ligand-induced functional dimerization of two subunits of a receptor-dimer pair. This assay detects GM-CSF-induced heterodimerization of the CSF2RA and CSF2RB receptors. The cells have been stably engineered to co-express CSF2RB fused to PK, and CSF2RA fused to EA. Binding of GM-CSF to the cytokine-specific CSF2RA receptor leads to heterodimerization with CSF2RB, leading to activation of intracellular signaling pathways. Receptor dimerization forces the two enzyme fragments to complement, resulting in the formation of a functional b-gal enzyme. The enzyme hydrolyzes a substrate to generate a chemiluminescent signal. Sargramostim binds to CSF2RA, stimulating receptor heterodimerization with the CSF2RB receptor, leading to an increase in signal. The bioassay kit contains all reagents needed for the assay including pre-qualified cryopreserved cells, detection reagents, cell plating reagent, positive control agonist, and assay plates.