Identification and Characterisation of Key Antigens from Neisseria meningitidis

Abstract

Neisseria meningitidis (Nm) is the causative organism of meningococcal meningitis and meningococcemia, and colonises the upper respiratory tract. Despite improved medical diagnosis and treatment strategies, meningococcal diseases are still major causes of death and disability. Prevention through vaccination is the most suitable approach for controlling disease. One approach to vaccine development is to identify potential protein antigens that can provide protective immunity and be incorporated into the next generation vaccines. A panel of ~100 recombinant outer membrane proteins (OMPs) were individually expressed, purified and used to generate a protein microarray chip that was used to screen antisera obtained from mice and human volunteers, who had been vaccinated with an outer membrane vesicle (OMV) vaccine. The IgG responses to each OMP were quantified and revealed antigens with the highest responses corresponding to integral OMPs (iOMPs), particularly the porins PorA and PorB, RmpM, OpcA and PilQ; in addition components of the Bam complex also responded well. The repertoires of highly responding antigens in humans and mice were similar but not identical. The relative dominance of response to iOMPs in humans and mice emphasizes the importance of this subclass of OMPs, and the need to conserve conformational integrity during vaccine selection and design. In a parallel project, the structure of another vaccine candidate, the Adhesin Complex Protein (ACP), was determined by x-ray crystallography. ACP adopts a β-barrel structure which is similar to a class of inhibitors which bind to lysozyme, suggesting that it adopts a similar function. This hypothesis was verified by biophysical binding studies and NMR, to generate a model for the ACP:lysozyme complex. It is proposed that ACP acts to prevent host-mediated lysozyme killing by binding to lysozyme, thus inhibiting the hydrolytic degradation of peptidoglycan (PGN). Further work also suggested that ACP interacts with bacterial PGN and selected complex saccharides, such as heparan sulphate and chondroitin sulphate. It is suggested that this function could promote immune tolerance and bacterial attachment to host cells.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Jeremy Derrick (Supervisor) & Nicola High (Supervisor)