SDF-1α and β are stromal derived CXC chemokines, and 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. Recombinant murine SDF-1β is a 8.5 kDa protein containing 72 amino acid residues.