Abstract
BackgroundPorcine contagious pleuropneumonia (PCP) is a highly contagious disease that is caused by Actinobacillus pleuropneumoniae (APP) and characterized by severe fibrinous necrotizing hemorrhagic pleuropneumonia, which is a severe threat to the swine industry. In addition to APP RTX-toxins I (ApxI), APP RTX-toxin II (ApxII), APP RTX-toxin III (ApxIII) and Outer membrane protein (OMP), there may be other useful antigens that can contribute to protection. In the development of an efficacious vaccine against APP, the immunogenicities of multicomponent recombinant subunit vaccines were evaluated.MethodsSix major virulent factor genes of APP, i.e., apxI, apxII, apxIII, APP RTX-toxins IV (apxIV), omp and type 4 fimbrial structural (apfa) were expressed. BALB/c mice were immunized with recombinant ApxI ( rApxI), recombinant ApxII (rApxII), recombinant ApxIII (rApxIII) and recombinant OMP (rOMP) (Group I); rApxI, rApxII, rApxIII, recombinant ApxIV (rApxIV), recombinant Apfa (rApfa) and rOMP (Group II); APP serotype 1 (APP1) inactivated vaccine (Group III); or phosphate-buffered saline (PBS) (Control group), respectively. After the first immunization, mice were subjected to two booster immunizations at 2-week intervals, followed by challenge with APP1 Shope 4074 and APP2 S1536.ResultsThe efficacy of the multicomponent recombinant subunit vaccines was evaluated on the basis of antibody titers, survival rates, lung lesions and indirect immunofluorescence (IIF) detection of APP. The antibody level of Group I was significantly higher than those of the other three groups (P < 0.05). The survival rate of Group I was higher than that of Groups II and III (P < 0.05) and the control (P < 0.01). Compared with the other three groups, the lungs of Group I did not exhibit obvious hemorrhage or necrosis, and only showed weak and scattered fluorescent dots by IIF detection.ConclusionThe result indicates that the multicomponent recombinant subunit vaccine composed of rApxI, rApxII, rApxIII and rOMP can provide effective cross-protection against homologous and heterologous APP challenge.
Highlights
Porcine contagious pleuropneumonia (PCP) is a highly contagious disease that is caused by Actinobacillus pleuropneumoniae (APP) and characterized by severe fibrinous necrotizing hemorrhagic pleuropneumonia [1], which is a severe threat to the swine industry
This study showed that a recombinant subunit vaccine consisting of rApxI, recombinant ApxII (rApxII), recombinant ApxIII (rApxIII) and recombinant OMP (rOMP) can protect mice effectively against challenge with APP serotype 1 (APP1) and APP2
We showed that the protective efficacy of the vaccine did not improve against APP1 and APP2 after recombinant Apfa (rApfa) was added to the vaccine containing rApxI, rApxII, rApxIII and rOMP
Summary
Porcine contagious pleuropneumonia (PCP) is a highly contagious disease that is caused by Actinobacillus pleuropneumoniae (APP) and characterized by severe fibrinous necrotizing hemorrhagic pleuropneumonia, which is a severe threat to the swine industry. Several studies have shown that effective protection can be provided by combined subunit vaccines composed of virulence factors of APP [9,10], such as transferrin-binding protein, lipoprotein [11], capsular polysaccharide [CPS] or lipopolysaccharide [LPS] [12]. Combined subunit vaccines, such as the multicomponent vaccine composed of APP RTX-toxins I (ApxI), APP RTX-toxin II (ApxII), APP RTX-toxin III (ApxIII) and Outer membrane protein (OMP), can provide higher protective efficacy against challenge with 12 serotypes of APP [13,14], which demonstrates that the development of multicomponent subunit vaccines should be pursued further
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