SDF-1α and β are stromal-derived, CXC chemokines that signal through the CXCR4 receptor. SDF-1α and β 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-1α and β contain the four highly conserved cysteine residues present in CXC chemokines. The mature SDF-1α protein is the result of alternative splicing of the SDF-1 gene and contains 68 amino acid residues. Recombinant Human SDF-1α is an 8.0 kDa protein containing 68 amino acid residues.