Secreted proteins of Neisseria meningitidis protect mice against infection.
Li Y., Wooldridge KG., Javed MA., Tang CM., Ala'aldeen DAA.
We addressed the hypothesis that meningococcal secreted proteins (MSPs) can elicit protective immunity against meningococcal disease. Endotoxin-depleted MSP preparations were used to immunise a group of 15 six-week-old BALB/c mice (25microg MSPs/dose mixed with Freund's complete adjuvant) on days 0, 14 and 21. Mice were challenged 2 weeks later with 10(7) colony forming units of live Neisseria meningitidis strain MC58 (serogroup B, ET-5). Negative and positive control groups of 15 mice each were injected with adjuvant only, or a live attenuated strain of MC58, respectively. Seven out of 15 mice (47%) from the negative control group died after 72h of challenge, whereas none of test or positive control group died. Protection afforded by the anti-MSP immune response can be at least partly attributed to complement-mediated bacterial lysis, detectable in vitro using the serum of immunised mice. Murine anti-MC58 MSP sera were bactericidal against homologous and five unrelated ET-5 serogroup B strains. However, failed to kill strains from other hypervirulent clonal lineages belonging to the same or different serogroups, despite the presence of cross-reactive antibodies detectable by immunoblotting. Similar sera raised against MSPs from an isolate belonging to the ET-37 electropherotype lineage were bactericidal against all tested isolates of this lineage and, in addition, against some but not all isolates belonging to the ET-5 lineage. FACS analysis of intact bacteria treated with anti-MSPs confirmed surface-binding of antibodies.