Cytokine that promotes the proliferation, survival and differentiation of monocytes and macrophages. Promotes the release of pro-inflammatory chemokines, and thereby plays an important role in innate immunity and in inflammatory processes. Plays an important role in the regulation of osteoclast proliferation and differentiation, and in the regulation of bone resorption. Signaling via CSF1R and its downstream effectors stimulates phosphorylation of MAPK1/ERK2 AND MAPK3/ERK1 (By similarity). Homodimer. Interacts with CSF1R (By similarity). Belongs to the IL-34 family.