IL-34 is secreted as a dimeric protein and currently belongs to no known cytokine family. It signals via the M-CSF Receptor, also known as CSF-1R and CD115, which is shared with M-CSF. IL-34 has no amino acid sequence homology to M-CSF, but they exhibit similarities in secondary structure and share overlapping functions. IL-34 has been shown to promote myeloid survival, proliferation, and differentiation, and to play a role in osteoclast formation. IL-34 expression has been detected in various tissues and is most abundant in the spleen.