title: Identification of <i>Neisseria lactamica</i> Outer Membrane Proteins Protective against Meningococcal Disease
Creators: name: Setchfield, Kerry Jane
Publisher: name: The Open University
Year: 2002

description: A number of approaches have been taken towards the development of a vaccine protective against serogroup B meningococcal disease but, as yet, none have been successful. The commensal bacterium, <i>Neisseria lactamica</i>, shares many surface structures with <i>N. meningitidis</i> and <i>N. lactamica</i> may therefore provide an alternative approach to vaccinating against serogroup B disease. Immunological evidence suggests that carriage of <i>N. lactamica</i> is involved in natural protection against disease caused by <i>N. meningitidis</i>. <br><br>This study presents the important observation that <i>N. lactamica</i> vaccines protect mice against meningococcal challenge. To identify the components responsible for protection, the outer membrane proteins of <i>N. lactamica</i>, extracted from whole cells, were separated by preparative electrophoresis and pooled into low &lt;43 kDa), medium (43-65 kDa) and high (&gt;67 kDa) molecular weight protein groups. The low molecular weight group provided the best protection of these groups, and further separation of this group indicated that proteins of 25-43 kDa provided the observed protection. Serum raised against <i>N. lactamica</i> proteins was cross-reactive with meningococci of different serogroups, serotypes and serosubtypes. <i>N. lactamica</i> antisera raised in mice were not bactericidal and although sera raised in rabbits showed some bactericidal activity, titres did not correlate with protection. <br><br>Meningococcal proteins cross-reactive with <i>N. lactamica</i> antisera were identified using surface enhance laser-desorption ionisation time-of-flight mass spectroscopy. The cross-reactive proteins had molecular masses of approximately 11.2 kDa, 13.7 kDa, 26.8 kDa, 17.4 kDa, 28.1 kDa, 33.1 kDa, 53.2 kDa and 66.6 kDa. Several meningococcal proteins of unknown function and others that have previously been considered as vaccine antigens (PorB and TbpB) were putatively identified. Proteins with epitopes homologous to these proteins are likely to be present in <i>N. lactamica</i> and may be involved in protection against meningococcal challenge. The identity of the 66.6 kDa protein as TbpB was confirmed by comparing the cross-reactivity of <i>N. meningitidis</i> OMPs from wild-type and TbpB knockout strains with <i>N. lactamica</i> antisera. <br><br>Using a <i>N. lactamica</i> genomic expression library, the DNA sequences of recombinant <i>N. lactamica</i> proteins cross-reactive with <i>N. lactamica</i> antiserum were obtained. Meningococcal proteins with homology to the <i>N. lactamica</i> sequences were identified by comparison with the complete genome sequences of <i>N. meningitidis</i> serogroups A and B. Fifteen cross-reactive sequences coded, either partially or completely, for 23 different proteins. <br><br>This study demonstrates that <i>N. lactamica</i> provides an effective vaccine in mice against lethal meningococcal challenge and that <i>N. lactamica</i> may provide an alternative approach to vaccination against serogroup B meningococcal disease. Putative identifications of the proteins involved in this protection have been made.