Characterization of two monoclonal antibodies directed against bactericidal/permeability-increasing protein

In this study the production and characterization of two monoclonal antibodies (MAbs), 4E3 and 5D7, against the bactericidal/permeability-increasing protein (BPI) were described. Using ELISAs, both 4E3 and 5D7 were shown to detect recombinant (r) BPI. Furthermore, natural BPI present in polymorphonuclear leukocytes (PMNL) was detected by both 4E3 and 5D7. The use of both MAbs in flow cytometry revealed that PMNL expressed low levels of cell-surface BPI. Lipopolysaccharide (LPS) was shown to block the interaction between anti-BPI MAb and rBPI. In addition, the MAbs blocked biologic activity of rBPI. The inhibition by BPI of LPS activation of the limulus amebocyte lysate assay and of LPS-induced tumor necrosis factor-alpha release by monocytes was prevented by 4E3 and 5D7. Both MAbs are specifically directed against BPI and can inhibit BPI bioactivity.