In contrast to JAK2V617F, JAK2ex13InDel does not require an exogenous homodimeric type 1 cytokine receptor to transform Ba/F3 cells, and is capable of activating β common chain family cytokine receptor (IL-3R, IL-5R, granulocyte-macrophage colony stimulating factor receptor) signaling in the absence of ligand, with the maximum effect observed for IL-5R, consistent with the clinical phenotype of eosinophilia.