Neisseria meningitidis is a major cause of meningitis and septicaemia in
infants and children. Disease caused by serogroup A, C, W-135 and Y strains is
prevented by vaccination using capsular polysaccharide preparations. For serogroup B
strains for which the capsular polysaccharide is poorly immunogenic, antigenic
proteins on the bacterial surface are under investigation as promising vaccine
candidates. Due to the variability in sequence of antigenic proteins, vaccine
formulations containing combinations of proteins and protein variants are tested for
broad protection against serogroup B isolates.
In search for new members for inclusion in multi-protein vaccines, the surface
proteome of N. meningitidis from MC58 strain was investigated using treatment of
whole meningococci with proteases followed by quantitative differential in-gel
electrophoresis (DIGE) of the meningococcal proteome. The majority of proteins
identified included known surface antigens and other uncharacterised predicted
surface proteins. Quantitative analysis also allowed the assessment of the extent of
protease cleavage on the protein population and suggested proteins were either
completely or partially digested. Additionally, differences in the protein content of
outer membrane vesicles (OMVs) from H44/76 meningococci grown in rich or
minimal culture media were assessed by DIGE. Differentially expressed proteins were
related to differences in bactericidal activity detected between immune sera from mice
immunised with the different OMV preparations. Of the proteins detected on the
surface and OMVs, those able to induce an immune response in mice were identified
by immunoproteome analysis.
Four of the previously uncharacterised proteins identified by the proteomic
analyses were assessed in immunological assays for their potential as vaccine candidates. Recombinant forms of macrophage infectivity potentiator (NmMIP), type
IV pili biogenesis proteins PilP and PilO and putative adhesin complex protein
NMB2095 were produced in Escherichia coli, purified and used to immunise mice.
Immune sera against NmMIP bound strongly to the surface of MC58 whilst exhibiting
opsonophagocytic activity and facilitating deposition of complement factors on the
surface of various meningococcal strains. The nucleotide sequence encoding NmMIP
was assessed across a panel of 106 meningococcal isolates and found to be highly
conserved and under negative selective pressure.