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Abstract: Actinobacillus pleuropneumoniae is a major respiratory pathogen of pigs; current vaccines provide only limited protection. AasP, a subtilisin-like serine protease, is a conserved outer membrane-localised autotransporter protein. We hypothesized that AasP would induce protective immunity and may thus constitute a useful component of a vaccine against A. pleuropneumoniae infection. Here we confirm experimentally that AasP is an antigenic in vivo-expressed protein. In pig protection studies, a detectable specific antibody response was induced in response to recombinant AasP. However, the vaccine was not capable of protecting pigs from colonization, infection or severe clinical disease resulting from challenge with the homologous A. pleuropneumoniae strain. [Copyright &y& Elsevier]

Abstract: 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 (25μg MSPs/dose mixed with Freund''s complete adjuvant) on days 0, 14 and 21. Mice were challenged 2 weeks later with 107 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. [Copyright &y& Elsevier]

Summary: Actinobacillus pleuropneumoniae is an important respiratory pathogen of swine, for which there is no highly effective vaccine. A phage expression library of the A. pleuropneumoniae genome was constructed and screened to identify potential vaccine components. Open reading frames within immuno-reactive phage were analyzed in silico to identify conserved outer membrane proteins. Four ORFs, named comL, lolB, lppC and ompA were chosen for further study. The four encoded proteins were shown experimentally to be antigenic, highly conserved, outer membrane, in vivo-expressed proteins. In pig protection studies, none of the proteins was individually capable of protecting pigs from colonization and infection with the homologous A. pleuropneumoniae strain, despite a detectable specific antibody response being induced. [Copyright &y& Elsevier]