Neutralization of Neisseria meningitidis outer membrane vesicles.

Introduction: We aimed to determine the neutralization of Neisseria meningitidis outer membrane vesicles (blebs) by humoral and cellular elements of whole blood.

Methods: The interaction of FITC-labeled blebs with monocytes was studied by spectrofluorometry. Blebs are able to induce an oxidative burst in neutrophils, and we evaluated the inhibitory effect of plasma on this process.

Results: Human plasma reduced the priming activity of blebs containing 1-3 ng/ml lipopolysaccharide (LPS) by 50-60% and bactericidal permeability increasing protein (BPI) reduced priming to background levels. A complete neutralization of LPS and blebs by plasma and BPI was measured using the limulus amebocyte lysate (LAL) assay. Furthermore, only 3% of blebs were cell-associated, while the remainder were in the supernatant.

Conclusions: Plasma and BPI are able to neutralize blebs, with phagocytosis playing only a minor role. As such, we conclude that blebs do not behave like particles but more like free LPS.