CXCL12/Stromal Cell-derived Factor 1 (SDF-1) is a member of the CXC chemokine ligand superfamily. Six alternatively spliced CXCL12/SDF-1 isoforms have been identified including, CXCL12/SDF-1 alpha, CXCL12/SDF-1 beta, and CXCL12/SDF-1 gamma. CXCL12/SDF-1 alpha is 89 amino acids (aa) in length with a predicted molecular weight of 10 kDa, CXCL12/SDF-1 beta is 93 aa in length with a predicted molecular weight of 10.6 kDa, and CXCL12/SDF-1 gamma is 119 aa in length with a predicted molecular weight of 13.7 kDa. The mouse CXCL12/SDF-1 orthologs share 99% aa sequence identity with the human protein. The alpha and beta isoforms are ubiquitously expressed while the gamma isoform is primarily expressed in the heart. CXCL12/SDF-1 isoforms are chemotactic for T lymphocytes and monocytes. It is cardio protective and has also been shown to hinder CXCR4-mediated HIV infection of T cells.