Abstract
Actinobacillus pleuropneumoniae (A. pleuropneumoniae/APP) is the pathogen that causes porcine contagious pleuropneumonia. Actinobacillus pleuropneumoniae is divided into 18 serovars, and the cross protection efficacy of epitopes is debatable, which has resulted in the slow development of a vaccine. Consequently, epitope-based vaccines conferring Actinobacillus pleuropneumoniae cross protection have rarely been reported. In this study, B cell epitopes in the head domain of trimeric autotransporter adhesin were predicted, and 6 epitopes were selected. Then, the predicted epitopes (Ba1, Bb5, C1, PH1 and PH2) were connected by linkers to construct a recombinant tandem antigen (rta) gene. The RTA protein encoded by the recombinant rta gene was expressed, and finally the ICR mice were immunized with the RTA protein with or without inactivated Actinobacillus pleuropneumoniae (serovars 1 and 5b) and challenged with Actinobacillus pleuropneumoniae to evaluate the protective effect of the epitope-based vaccine and combined vaccine. The mice in the RTA-immunized group and RTA plus inactivated Actinobacillus pleuropneumoniae vaccine group had a significant improvement in clinical symptoms and a higher level of antibody in the serum than those in the control group. The RTA immune group had a 40% survival rate after Actinobacillus pleuropneumoniae infection, whereas the combination of RTA and inactivated Actinobacillus pleuropneumoniae produced very strong cross immune protection in mice, at least 50% (RTA IB1 + C5) and at most 100% (RTA IB5 + C1), whereas no cross immunoprotection was found in the solo Actinobacillus pleuropneumoniae immune group. Overall, the combination of the RTA protein and inactivated bacteria significantly enhanced the cross protection effects. This implies that RTA protein in combination with a suitable inactivated Actinobacillus pleuropneumoniae strain could be a candidate vaccine for porcine contagious pleuropneumonia.
Highlights
Porcine contagious pleuropneumonia caused by A. pleuropneumoniae is a serious respiratory infectious disease in pigs
Design of the rta gene and prokaryotic expression and purification of the The capital letter of rta (RTA) protein To identify the effective epitope of ADH, trimeric autotransporter adhesin (TAA) was analyzed by daTAA software, which showed that the Ylhead-binding sequence was densely distributed in the 124–612 aa region of ADH (Fig. 1a)
The RTA protein was expressed under optimal conditions, the cells were lysed by sonication, and the protein was purified by Ni–NTA affinity chromatography
Summary
Porcine contagious pleuropneumonia caused by A. pleuropneumoniae is a serious respiratory infectious disease in pigs. It often causes acute outbreaks and is characterized by a high mortality rate, which causes very large economic losses in the global pig industry (Jeffrey et al 2012). There are 18 serovars of A. pleuropneumoniae (Bosse et al 2018; Liu et al 2018), and the lack of cross immunoprotection among the major serovars has slowed the development of a vaccine. Apx toxins can be divided into four types, Apx I-IV; Apx IV exists in all serovars of A. pleuropneumoniae strains (Schaller et al 1999) and is necessary for virulence (Liu et al 2009). Due to the complicated structure, the large size of the protein and limited effective epitopes, the subunit structure is not the best option for vaccine development
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