Vitamin D Binding Protein is a secreted multifunctional protein found in plasma, ascitic fluid, cerebrospinal fluid and urine, and on the surface of many cell types. In plasma, it carries the vitamin D sterols and prevents polymerization of actin by binding its monomers. DBP associates with membrane bound immunoglobulin on the surface of B lymphocytes and with IgG fc receptor on the membranes of T lymphocytes.