Basigin (BSG) also known as extracellular matrix metalloproteinase inducer (EMMPRIN) or cluster of differentiation 147 (CD147) is a protein that in humans is encoded by the BSG gene. This protein is a determinant for the Ok blood group system. There are three known antigens in the Ok system; the most common being Oka (also called OK1), OK2 and OK3. Basigin has been shown to be an essential receptor on red blood cells for the human malaria parasite, Plasmodium falciparum. The common isoform of basigin (basigin-2) has two immunoglobulin domains, and the extended form basigin-1 has three. Function Basigin is a member of the immunoglobulin superfamily, with a structure related to the putative primordial form of the family. As members of the immunoglobulin superfamily play fundamental roles in intercellular recognition involved in various immunologic phenomena, differentiation, and development, basigin is thought also to play a role in intercellular recognition (Miyauchi et al., 1991; Kanekura et al., 1991). It has a variety of functions. In addition to its metalloproteinase-inducing ability, basigin also regulates several distinct functions, such as spermatogenesis, expression of the monocarboxylate transporter and the responsiveness of lymphocytes. Basigin is a type I integral membrane receptor that has many ligands, including the cyclophilin (CyP) proteins Cyp-A and CyP-B and certain integrins. Basigin also serves as a receptor for S100A9 and platelet glycoprotein VI, and basigin-1 acts as a receptor for the rod-derived cone viability factor. It is expressed by many cell types, including epithelial cells, endothelial cells, neural progenitor cells and leukocytes. The human basigin protein contains 269 amino acids that form two heavily glycosylated C2 type immunoglobulin-like domains at the N-terminal extracellular portion. A second form of basigin has also been characterized that contains one additional immunoglobulin-like domain in its extracellular portion. Interactions Basigin has been shown to interact with Ubiquitin C. Basigin has been shown to form a complex with monocarboxylate transporters in the retina of mice. Basigin appears to be required for proper placement of MCTs in the membrane. In the Basigin null mouse, the failure of MCTs to integrate with the membrane may be directly linked to a failure of nutrient transfer in the retinal pigmented epithelium (the lactates transported by MCTs 1, 3, and 4 are essential nutrients for the developing RPE), resulting in loss of sight in the null animal. Basigin interacts with the fourth C-type lectin domain in the receptor Endo180 to form a