IL-34 is a homodimeric cytokine that is expressed in a range of tissues that include spleen, heart, brain, liver, kidney, lung, ovary, thymus, testis, small intestine, prostate and colon. IL-34 is a ligand for colony-stimulating factor-1 receptor (CSF1R), which also binds to CSF-1. It specifically binds CD14+ monocytes, promotes survival and proliferation of human peripheral blood monocytes, and stimulates macrophage colony formation by human bone marrow cells. IL-34, like human CSF-1, stimulates phosphorylation of MAPK1/ERK2 and MAPK3/ERK1. Recombinant Human IL-34 is a 52.5 kDa homodimeric glycoprotein consisting of 460 amino acid residues, including a C-terminal His-Tag.