Bactericidal/Permeability Increasing Protein (BPI)

BPI was initially identified in neutrophils, but is found in other tissues including the epithelial lining of mucus membranes. It is an endogenous antibiotic protein with potent killing activity against some bacteria (Gram-negative bacteria). It binds to compounds called lipopolysaccharides produced by Gram-negative bacteria. Lipolysaccharides are potent activators of the immune system, however BPI at certain concentrations can prevent this activation.

Because lipopolysaccharides are potent inflammatory agents, and the action of antibiotics can result in the release of these compounds, the binding capacity of BPI was explored as a possible means of reducing injury. Xoma Ltd. developed a recombinant 25kDa portion of the BPI molecule called rBPI₂₁, NEUPREX or opebecan.