Characterisation of the Immunomodulatory Effects of Meningococcal Opa Proteins on Human Peripheral Blood Mononuclear Cells and CD4+ T Cells

The potential utility of liposomes for Neisseria vaccines

INTRODUCTION

Species of the genus Neisseria are important global pathogens. Neisseria gonorrhoeae (gonococcus) causes the sexually transmitted disease gonorrhea and Neisseria meningitidis (meningococcus) causes meningitis and sepsis. Liposomes are self-assembled spheres of phospholipid bilayers enclosing a central aqueous space, and they have attracted much interest and use as a delivery vehicle for Neisseria vaccine antigens.

AREAS COVERED

A brief background on Neisseria infections and the success of licensed meningococcal vaccines are provided. The absence of a gonococcal vaccine is highlighted. The use of liposomes for delivering Neisseria antigens and adjuvants, for the purposes of generating specific immune responses, is reviewed. The use of other lipid-based systems for antigen and adjuvant delivery is examined briefly.

EXPERT OPINION

With renewed interest in developing a gonococcal vaccine, liposomes remain an attractive option for delivering antigens. The discipline of nanotechnology provides additional nanoparticle-based options for gonococcal vaccine development. Future work would be needed to tailor the composition of liposomes and other nanoparticles to the specific vaccine antigen(s), in order to generate optimal anti-gonococcal immune responses. The potential use of liposomes and other nanoparticles to deliver anti-gonococcal compounds to treat infections also should be explored further.

Unaltered Fungal Burden and Lethality in Human CEACAM1-Transgenic Mice During Candida albicans Dissemination and Systemic Infection

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1, CD66a) is a receptor for Candida albicans. It is crucial for the immune response of intestinal epithelial cells to this opportunistic pathogen. Moreover, CEACAM1 is of importance for the mucosal colonization by different bacterial pathogens. We therefore studied the influence of the human CEACAM1 receptor in human CEACAM1-transgenic mice on the C. albicans colonization and infection utilizing a colonization/dissemination and a systemic infection mouse model. Our results showed no alterations in the host response between the transgenic mice and the wild-type littermates to the C. albicans infections. Both mouse strains showed comparable C. albicans colonization and mycobiota, similar fungal burdens in various organs, and a similar survival in the systemic infection model. Interestingly, some of the mice treated with anti-bacterial antibiotics (to prepare them for C. albicans colonization via oral infection) also showed a strong reduction in endogenous fungi instead of the normally observed increase in fungal numbers. This was independent of the expression of human CEACAM1. In the systemic infection model, the human CEACAM1 expression was differentially regulated in the kidneys and livers of Candida-infected transgenic mice. Notably, in the kidneys, a total loss of the largest human CEACAM1 isoform was observed. However, the overwhelming immune response induced in the systemic infection model likely covered any CEACAM1-specific effects in the transgenic animals. In vitro studies using bone marrow-derived neutrophils from both mouse strains also revealed no differences in their reaction to C. albicans. In conclusion, in contrast to bacterial pathogens interacting with CEACAM1 on different mucosal surfaces, the human CEACAM1-transgenic mice did not reveal a role of human CEACAM1 in the in vivo candidiasis models used here. Further studies and different approaches will be needed to reveal a putative role of CEACAM1 in the host response to C. albicans.

Helicobacter pylori outer membrane vesicles inhibit human T cell responses via induction of monocyte COX-2 expression

The modulation of T cell responses by Helicobacter pylori is thought to potentiate both H. pylori persistence and development of gastric pathologies including cancer. Release of outer membrane vesicles (OMV) by H. pylori provides a potential vehicle for modulation of the immune system. Although OMV are thought to have T cell suppressive activity, this has not yet been demonstrated. Their suppressive activity was investigated in this study using the responses of peripheral blood mononuclear cells (PBMC) to T cell stimuli as a readout. We demonstrate that addition of OMV to PBMC significantly inhibits subsequent T cell proliferation in a cyclo-oxygenase-2 (COX-2)-dependent manner. Addition of OMV did not significantly modulate PBMC apoptosis, but induced strong expression of COX-2 by the monocytes present and significantly increased levels of PGE2 and IL-10. These effects were independent of vacuolating cytotoxin expression. Together, these findings demonstrate that OMV can suppress human T cell responses and that the predominant mechanism is not through a direct effect on the T cells but results from the induction of COX-2 expression in monocytes. This increased COX-2 activity may modulate not only H. pylori-directed immune responses but also wider immune responses.

Spheres of Hope, Packets of Doom: the Good and Bad of Outer Membrane Vesicles in Interspecies and Ecological Dynamics

Outer membrane vesicles (OMVs) are proteoliposome nanoparticles ubiquitously produced by Gram-negative bacteria. Typically bearing a composition similar to those of the outer membrane and periplasm of the cells from which they are derived, OMVs package an array of proteins, lipids, and nucleic acids. Once considered inconsequential by-products of bacterial growth, OMVs have since been demonstrated to mediate cellular stress relief, promote horizontal gene transfer and antimicrobial activity, and elicit metazoan inflammation. Recently, OMVs have gained appreciation as critical moderators of interorganismal dynamics. In this review, we focus on recent progress toward understanding the functions of OMVs with regard to symbiosis and ecological contexts, and we propose potential avenues for future OMV studies.