Purity >95% by SDS-PAGE, MW: 8 kDa. Stromal cell-derived factor-1 alpha (SDF-1a), also called CXCL12a, is one of two SDF-1 splice variants made by a wide variety of cells upon stimulation by inflammatory cytokines such as tumor necrosis factors (TNF), interleukin 1 (IL-1), and lipopolysaccharide (LPS). SDF-1a signals through the G protein-coupled receptor CXCR4 to recruit activated leukocytes. Human and mouse SDF-1a share 99% sequence identity.