A1BG (alpha-1B-glycoprotein) is a plasma protein and is a member of the immunoglobulin superfamily. A1BG contains 474 amino acids and has 5 intrachain disulfide bonds. It has been reported that cysteine-rich secretory protein 3 (CRISP-3) is a specific and high-affinity ligand of A1BG. A1BG-CRISP-3 complex displays a similar function in protecting the circulation from a potentially harmful effect of free CRISP3 .