Monocyte/macrophage lineage development and function in the steady state and during inflammation are heavily influenced by cytokines, including macrophage-colony stimulating factor (M-CSF or CSF-1) and granulocyte macrophage-CSF (GM-CSF). In the steady state, CSF-1 controls the development of certain populations of tissue macrophages and blood monocytes, as well as specific dendritic cell (DC) subsets, while another CSF-1 receptor ligand, IL-34, does so for microglia and epidermal Langerhans cells; on the other hand, GM-CSF controls the normal development of alveolar macrophages and certain gut and skin DC populations. With respect to inflammation and host defense, macrophage populations have been categorised for convenience into M1 and M2 “polarization” and/or “activation” states following cytokine treatment, an approach which of necessity is simplistic in nature. The respective contributions of GM-CSF and CSF-1 to macrophage lineage “activation” or phenotypes is discussed as is the data resulting from their in vivo blockade in models of inflammation/autoimmunity.

Disclosure of Interest None Declared