MBP-1 (eosinophil major basic protein), also known as PRG2 (proteoglycan 2) can be found in two forms: a 33 kDa glycosylated secreted proprotein form that circulates especially in pregnancy, or a 14 kDa mature protein. Covalent association with proMBP-1 inhibits the activity of proteins such as PAPP-A (pregnancy-associated plasma protein-A), heparanase and angiotensinogen. In contrast, mature MBP-1 is present in eosinophil and basophil granules and mainly plays an antimicrobial role.