Interleukin 34 (IL-34) is well known for its ability to induce the formation of colony-forming unit macrophages in human bone marrow cell cultures (Foucher et al.; Wei et al.). This dimeric glycoprotein is a member of the short-chain helical hematopoietic cytokine family (Baghdadi et al.; Foucher et al.), and exists in two isoforms that differ by a single glutamine (Chen et al.; Foucher et al; Wei et al.). IL-34 interacts with M-CSF to trigger tyrosine phosphorylation of the receptor and ERK1/2 pathways. (Wang et al.; Wei et al.). It is expressed in many tissues (heart, brain, lung, liver, kidney, thymus, testes, ovary, small intestine, prostate, and colon), with the highest expression in the spleen. In combination with RANKL (Catalog #78214), IL-34 induces osteoclast differentiation (Chen et al.; Foucher et al.). IL-34 expression is decreased in Alzheimer’s disease and atopic dermatitis, while high levels of IL-34 are found in many types of cancer correlated with poor prognosis, chronic heart failure or coronary artery disease, inflammatory bowel disease, influenza A infection, during acute liver transplant rejection or in non-alcoholic fatty liver disease, and with rheumatoid arthritis (Baghdadi et al.). It is therefore a possible pharmacological target for treating bone or inflammatory diseases (Chen et al.). This protein contains a His-residue tag at the carboxyl end of the polypeptide chain, and the protein was purified as a homodimer consisting of 39 kDa monomers (Lin et al.).