Meningococcal Outer Membrane Vesicle Composition-Dependent Activation of the Innate Immune Response

Abstract

cMeningococcal outer membrane vesicles (OMVs) have been extensively investigated and successfully implemented as vaccines. They contain pathogen-associated molecular patterns, including lipopolysaccharide (LPS), capable of triggering innate immunity. However, Neisseria meningitidis contains an extremely potent hexa-acylated LPS, leading to adverse effects when its OMVs are applied as vaccines. To create safe OMV vaccines, detergent treatment is generally used to reduce the LPS content. While effective, this method also leads to loss of protective antigens such as lipoproteins. Alternatively, genetic modification of LPS can reduce its toxicity. In the present study, we have compared the effects of standard OMV isolation methods using detergent or EDTA with those of genetic modifications of LPS to yield a penta-acylated lipid A (lpxL1 and pagL) on the in vitro induction of innate immune responses. The use of detergent decreased both Toll-like receptor 4 (TLR4) and TLR2 activation by OMVs, while the LPS modifications reduced only TLR4 activation. Mutational removal of PorB or lipoprotein factor H binding protein (fHbp), two proteins known to trigger TLR2 signaling, had no effect, indicating that multiple TLR2 ligands are removed by detergent treatment. Detergent-treated OMVs and lpxL1 OMVs showed similar reductions of cytokine profiles in the human monocytic cell line MM6 and human dendritic cells (DCs). OMVs with the alternative penta-acylated LPS structure obtained after PagL-mediated deacylation showed reduced induction of proinflammatory cytokines interleukin-6 (IL-6) and IL-1␤ but not of IP-10, a typical TRIF-dependent chemokine. Taken together, these data show that lipid A modification can be used to obtain OMVs with reduced activation of innate immunity, similar to what is found after detergent treatment. G ram-negative bacteria have the ability to naturally shed vesicles from the outer membrane. These spontaneous outer membrane vesicles (sOMVs) are composed of lipids, outer membrane proteins, lipopolysaccharide (LPS), and some periplasmic proteins. Shedding of sOMVs occurs without significant disruption in the integrity of the cell, and release of vesicles is increased by bacterial stress responses (1, 2). Some of the proposed functions of shedding of outer membrane blebs include protection and transport of secreted molecules, interaction with host cells, evasion of immunity by action as a decoy for antibodies and other antibacterial molecules, and action as nucleators in biofilm formation (3).The fact that OMVs are nonreplicating structures that contain many crucial surface components and virulence factors, in combination with pathogen-associated molecular patterns (PAMPs) that trigger innate immune responses, makes them attractive as candidate vaccines. This is evidenced by the successful control of meningococcal serogroup B epidemics using OMV vaccines (4-6) and experimental studies that have explored the vaccine potential of OMVs against other bacterial pathogens (7, 8). The isolation of OMVs from Neiss...

Natural and engineered bacterial outer membrane vesicles

“…Compared to traditional method like chemical modification based on the structure of LPS or LTA, the biosafety of OMV will be improved after the rational genetic manipulation, which will further increase the therapeutic potential of OMV . Some studies have shown that OMVs from genetically engineered bacteria such as E. coli, Neisseria meningitidis and S. aureus show low toxicity and can effectively induce antibody-mediated immunity or innate immune response (Fantappie et al 2014;Zariri et al 2016).…”

Bacterial Outer Membrane Vesicles from Dextran Sulfate Sodium–Induced Colitis Differentially Regulate Intestinal UDP-Glucuronosyltransferase 1A1 Partially Through Toll-Like Receptor 4/Mitogen-Activated Protein Kinase/Phosphatidylinositol 3-Kinase Pathway

“…Low-LPS OMVs were prepared according to previous reports (Claassen et al, 1996;Zariri et al, 2016) with minor modifications. Briefly, the bacterial cultures were pelleted as described above and resuspended in 0.1 M Tris-10 mM EDTA buffer.…”

Bacterial Membrane Vesicles: New Therapeutic Prospectives

“…Clostridium difficile, Porphyromonas gingivalis, Neisseria meningitidis and Staphylococcus aureus have displayed immunological outcomes, including those mediated by TLR2 and TLR4 [1][2][3][4][5]. Moreover, in vitro transcriptome analysis suggested that LPS structural changes can be used to alter immunological outcome [6].…”