Bactericidal/Permeability-Increasing Protein, a Lipopolysaccharide-Specific Protein on the Surface of Human Peripheral Blood Monocytes

Abstract

Bactericidal/permeability-increasing protein (BPI), a cationic protein present in the azurophilic granule and on the surface of polymorphonuclear leukocytes, specifically interacts with lipopolysaccharide (LPS). This study demonstrates for the first time, using flow cytometry with specific anti-BPI monoclonal antibody (MAb), that human peripheral blood monocytes express BPI on their cell surface. The monocyte cell surface BPI was shown to bind to LPS, because binding of anti-BPI MAb 4E3 (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 LPS. However, cell surface BPI did not quantitatively contribute to the interaction of LPS with the monocyte cell membrane, since preincubation of cells with 4E3 did not block binding of LPS-fluorescein isothiocyanate to monocytes. The origin of the monocyte cell surface BPI remains to be further elucidated.

Bactericidal/permeability‐increasing protein inhibits endotoxin‐induced vascular nitric oxide synthesis

“…It is present in the primary granules of neutrophils (13) and specific granules of eosinophils (14) but can also be detected on the surface of polymorphonuclear leukocytes (15) and monocytes (16). BPI is an endogenous antibiotic and as such part of the innate defence against infection.…”

Bacteria in the Intestine, Helpful Residents or Enemies from Within?

“…It was first found to be present in the azurophilic granules of neutrophils by Weiss and colleagues, and it is thought to be the most potent component in nonoxidative killing mediated by these cells (152). More recently, BPI has also been shown to be expressed on the surface of neutrophils (148), on the surface of monocytes (24), in the granules of eosinophils (11), and in fibroblasts (122). Functional BPI is expressed in IEC and in the epithelium at other mucosal sites (13).…”

The bactericidal/permeability-increasing protein (BPI) in infection and inflammatory disease

“…BPI was also detected on the surface of neutrophils and monocytes [31,32], in both cases presumably originating from degranulation of neighboring activated neutrophils. In myeloid cells, BPI is expressed mainly during the promyelocytic and myelocytic stages of neutrophilic maturation, consistent with storage of BPI in azurophilic granules [33,34].…”