Bactericidal/permeability-increasing protein

Bactericidal/permeability-increasing protein (BPI) is a 456-residue (~50kDa) protein that is part of the innate immune system.

Distribution and function
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 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.

BPI was discovered by Jerrold Weiss and Peter Elsbach at New York University Medical School.

rBPI21
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. In a trial, it was found to decrease the mortality of Gram-negative bacterial-induced sepsis. Studies suggest that its binding activity is not the means by which it mediates its protective effect. Studies show biological effects with Gram-positive bacteria and even in infection by the protozoan, Toxoplasma gondii.