Outer membrane vesicles from Neisseria meningitidis

Abstract

Flow cytometry was used to study the expression of leukocyte adhesion molecules CD11a, CD11b, CD11c, CD14, and CD62L (L-selectin) and production of reactive oxygen species (ROS) in an ex vivo human whole-blood system stimulated with lipopolysaccharide-containing outer membrane vesicles (LPS-OMV) from N. meningitidis. Results demonstrated a dose-dependent increase in surface expression of CD11a, CD11b, CD11c and CD14 in granulocytes and monocytes (maximal at 30-120 min) upon OMV-LPS challenge, whereas CD62L expression was heavily downregulated (maximal at 30-120 min). The OMV-associated LPS was almost as potent (on a weight basis) as purified LPS from E. coli in inducing adhesion molecule modulation but the response was delayed. Upon stimulation with OMV-LPS or E. coli-LPS, the production of intracellular ROS increased in both granulocytes and monocytes when dihydroethidium (DHE, mainly reflecting superoxide anion) was used as a probe, whereas peroxynitrite production monitored with dihydrorhodamine 123 (DHR) was not significantly changed. The OMV-mediated modulation of leukocyte adhesion molecule expression and increased ROS production may certainly lead to increased entrapment of leukocytes in the microcirculation and contribute to untoward inflammatory reactions as seen in systemic meningococcal disease.

Effect of an extract of the mushroom Agaricus blazei Murill on expression of adhesion molecules and production of reactive oxygen species in monocytes and granulocytes in human whole blood ex vivo

“…The downregulation of CD62L in monocytes and granulocytes is probably explained by the localization of CD62L exclusively to the plasma membrane (19) and shedding following stimulation (20). Recently, the inverse relationship of CD62L and CD11b expression was also reported after stimulation of whole blood with meningococcal LPS in a similar experimental set‐up as used here (21). The fractional LPS component in AbM could definitely not explain the adhesion molecule modulating properties of AbM.…”

“…The fractional LPS component in AbM could definitely not explain the adhesion molecule modulating properties of AbM. In fact, even the highest AbM concentration used in the present experiments represented a LPS concentration that was far below the minimum dose of E. coli – or meningococcal LPS necessary to induce adhesion molecule changes under similar experimental conditions (21). Interestingly, changes of these adhesion molecules induced by AbM occurred at lower concentrations in monocytes than in granulocytes, which may imply that AbM stimulates via additional signaling pathways in monocytes.…”