The biotinylated antibody of the Rat CXCL 12 / SDF-1 Alpha ELISA Assay kit binds to the streptavidin coated microtiter plate. The SDF-1 α of the standards/samples binds to this antibody and is detected by the primary antibody. The biotinylated antibody, the primary antibody and the standards/samples are incubated on the microtiter plate altogether at the same time. The primary antibody, which is bound to SDF-1 Alpha, is then detected by a secondary peroxidase-conjugated antibody. The reaction with the substrate is stopped by addition of acid and the blue colour turns to yellow. The measured absorbance is directly proportional to the quantity of SDF-1 Alpha. Sample Types: serum, plasma. Range: 1.25 - 30 ng/ml. Sensitivity: 1.25 ng/ml. Time: 2.5 hours ? SDF-1 Alpha (CXCL12) is a CXC chemokine (1). The small basic protein (ca. 8 kDa) has no glycosylation site in its sequence (2). The homology properties of SDF-1 Alpha are unique among the chemokines. It has a high degree of conservation within the mammalians, with 99 % identity between the human and the murine SDF-1 Alpha sequences. But it shows a weak homology to the other CXC chemokines and the SDF-1 gene is on chromosome 10, whereas the other chemokine genes are on chromosome 4 and 17 (3). Except for SDF-1 Alpha there is another isoform of this chemokine, SDF-1β. SDF-1 Alpha and SDF-1β result from alternative splicing (1). SDF-1 Alpha binds to and activates the receptors CXCR4 and CXCR7 (1), whereupon SDF-1 Alpha is the only known ligand for CXCR4 (2). SDF-1 Alpha binds also to fibronectin-1 [4], several glycosaminoglycans and heparin (5). SDF-1 Alpha is constitutively expressed by bone marrow stromal cells (1) and many other tissues (for example heart, liver, brain, muscle, kidney) (3). Mouse to human, there are two amino acid differences in the sequence of SDF-1 alpha and there is one different amino acid in rat SDF-1 alpha. Until today here is a limited number of papers on studies on quantitative measurement of SDF-1 alpha in rat samples.