Vitamin D BP (VitD BP), also called VDB, DBP, Group Specific Component (Gc) or macrophage-activating factor (DBP- or Gc-MAF), is a member of the albumin family. These plasma/body fluid proteins have a conserved pattern of cysteine motifs that form binding domains. VitD BP is predominantly produced by hepatic parenchymal cells. It transports VitD, activates macrophages and osteoclasts, and enhances C5a chemotactic activity. Over 80 variant alleles have been identified, some of which correlate with osteoporosis or prostate cancer. Human and mouse VitD BP share 78% aa identity.