BACTERICIDA ERMEABILITY-INCREASING PROTEIN, A LIPOPOLYSACCHARIDE-SPECIFIC PROTEIN ON THE SURFACE OF HUMAN PERIPHERAL-BLOOD MONOCYTES

Bactericidal/permeability-increasing protein (BPI), a cationic protein present in the azurophilic granule and on the surface of polymorphonu clear leukocytes, specifically interacts with lipopolysaccharide (LPS) . This study demonstrates for the first time, using flow cytometry wit h specific anti-BPI monoclonal antibody (MAb), that human peripheral b lood monocytes express BPI on their cell surface. The monocyte cell su rface BPI was shown to bind to LPS, because binding of anti-BPI MAb 4E 3 (which is known not to react with BPI to which LPS is bound) to cell surface BPI was strongly reduced after preincubation of cells with LP S. However, cell surface BPI did not quantitatively contribute to the interaction of LPS with the monocyte cell membrane, since preincubatio n of cells with 4E3 did not block binding of LPS-fluorescein isothiocy anate to monocytes. The origin of the monocyte cell surface BPI remain s to be further elucidated.