IL-3 ,IL-5 and GM-CSF constitute an important subfamily of cytokines which play a role in the proliferation and maturation of myeloid cells. All three cytokines have been implicated in maturation of myeloid cell lineage. IL-5 appears to be particularly important in eosinophil and mast cell biology. IL-5 also plays a role in B cell immune response. IL-3 influences the the proliferation and maturation of stem cells, as well as progenitors of granulocyte, macrophage and basophil lineages. GM-CSF functions as a growth factor for granulocyte,macrophage and eosinophil lineages.

The receptor consists of alpha (ligand specific) subunit and beta (activating) subunit. The beta chain which associates with JAK2, promotes activation of JAK2 and STAT5 pathways.