Inhibition of Lps-Mediated Responses in Human Whole Blood by Recombinant Bactericidal/Permeability Increasing Protein

Abstract

BPI is a LPS-binding protein with bactericidal and LPS-neutralizing activity that is found in the azurophilic granules of neutrophils. Since an N-terminal proteolytic fragment of BPI displays the potent biological properties of the 55 kD intact protein (BPI₅₅), we have produced, purified, and characterized, a recombinant protein, rBPI₂₃, corresponding to the N-terminal half of human BPI. rBPI₂₃ binds specifically and with high affinity to highly purified smooth LPS isolated from a variety of clinical isolates via rBPI₂₃ interaction with the lipid A region. We investigated the ability of rBPI₂₃ to inhibit LPS-mediated, cellular responses in whole human blood, a complex environment which more closely resembles the in vivo situation. We observed that rBPI₂₃ inhibited the LPS-dependent production of a variety of inflammatory cytokines, including TNF, IL-1β, IL-6, and IL-8. This response was specific in that rBPI₂₃ had no effect on the ability of irrelevant stimuli (i.e., zymosan) to induce these cytokines. The LPS dependent production of oxygen-derived free radicals by human blood cells, resulting in chemiluminescence, was also inhibited by rBPI23. Again, this inhibition was specific in that rBPI₂₃ had no effect on the ability of irrelevant stimuli (PMA or zymosan) to induce chemiluminescence. In the complex setting of whole human blood, LPS-dependent chemiluminescence was found to be independent of the presence of TNF, as antibodies to TNF had no effect in this system. The profound effects of rBPI₂₃ on the LPS-mediated, Cellular responses in whole blood suggest that BPI has promise as a therapeutic agent in Gramnegative infections.