C-X-C motif chemokine 12 beta (CXCL12-beta) is a 72 amino acid Cys-X-Cys chemokine that is involved in diverse cellular functions including embryogenesis, immune surveillance, inflammation response, tissue homeostasis, and tumor growth and metastasis. CXCL12 is also known as stromal cell-derived factor 1 (SDF-1) and is processed after secretion by proteolytic cleavage to the 68 amino acid CXCL12-alpha/SDF-1-alpha. The C-terminal processing to isoform CXCL12-alpha is reduced by binding to heparin and cell surface proteoglycans. CXCL12 is a ligand for the G protein coupled receptor CXCR4 and is chemotactic for lymphocytes and monocytes but not neutrophils. CXCL12 also binds to atypical chemokine receptor ACKR3 which activates the beta-arrestin pathway and acts as a scavenger receptor for SDF-1. CXCL12-alpha demonstrates reduced chemotactic activity. CXCL12 is ubiquitously expressed in all tissues with highest levels detected in the liver, pancreas and spleen. CXCL12 directs the migration of hematopoietic cells from liver to bone marrow for myelopoiesis, B-cell lymphopoiesis, large blood vessel formation, and heart ventricular septum formation during embryogenesis. During adulthood CXCL12 plays an important role in angiogenesis by recruiting endothelial progenitor cells from the bone marrow and may be protective after myocardial infarction. CXCL12 inhibits CXCR4-mediated infection by T-cell line-adapted HIV-1 and mutations in CXCL12 are associated with resistance to HIV-1 infection. Cytokines are a family of secreted proteins involved in immunoregulatory and inflammatory processes. The CXC cytokines are chemotactic cytokines characterized by two cysteines separated by one amino acid that induce directed chemotaxis in nearby responsive cells. Recombinant human CXCL12 beta from Molecular Innovations is provided as a native untagged protein. This chemokine is expressed in E. coli then processed, refolded and purified to yield the native, secreted form of the mature chemokine. >98percent pure by SDS-PAGE, HPLC, MALDI-MS and NMR analysis. CXCR4 activity verified by intracellular calcium flux using THP1 cells as described by Veldkamp et al, Science Signaling 2008. Add deionized water to desired volume, aliquot and freeze unused portion.