SDF-1alpha and beta are stromal-derived, CXC chemokines that signal through the CXCR4 receptor. SDF-1alpha and beta chemoattract B and T cells, and have been shown to induce migration of CD34+ stem cells. Additionally, the SDF-1 proteins exert HIV-suppressive activity in cells expressing the CXCR4 receptor. Human and murine SDF-1 proteins act across species. SDF-1alpha and beta contain the four highly conserved cysteine residues present in CXC chemokines. The mature SDF-1beta protein, produced by an N-terminal truncation of two additional amino acids, after removal of the signal sequence, contains 72 amino acid residues. Recombinant Rat SDF-1beta is an 8.4 kDa protein containing 72 amino acid residues.