– Vitamin D-Binding Protein (DBP) is a member of the ALB/AFP/VDB family. DBP is a secreted protein and contains three albumin domains. The primary structure contains 28 cysteine residues forming multiple disulfide bonds. DBP acts as a multifunctional protein found in plasma, ascitic fluid, cerebrospinal fluid, and urine and on the surface of many cell types. DBP binds to vitamin D and its plasma metabolites and transports them to target tissues. DBP associates with membrane-bound immunoglobulin on the surface of B-lymphocytes and with IgG Fc receptor on the membranes of T-lymphocytes.