AasP autotransporter protein of Actinobacillus pleuropneumoniae does not protect pigs against homologous challenge

Actinobacillus pleuropneumoniae, surface proteins and virulence: a review

Actinobacillus pleuropneumoniae (App) is a globally distributed Gram-negative bacterium that produces porcine pleuropneumonia. This highly contagious disease produces high morbidity and mortality in the swine industry. However, no effective vaccine exists to prevent it. The infection caused by App provokes characteristic lesions, such as edema, inflammation, hemorrhage, and necrosis, that involve different virulence factors. The colonization and invasion of host surfaces involved structures and proteins such as outer membrane vesicles (OMVs), pili, flagella, adhesins, outer membrane proteins (OMPs), also participates proteases, autotransporters, and lipoproteins. The recent findings on surface structures and proteins described in this review highlight them as potential immunogens for vaccine development.

Actinobacillus pleuropneumoniae Interaction With Swine Endothelial Cells

Actinobacillus pleuropneumonia is a swine (host) specific respiratory pathogen and the etiological agent of swine pleuropneumonia which affects pigs of all ages, many being asymptomatic carriers. This pathogen has high morbidity and mortality rates which generates large economic losses for the pig industry. Actinobacillus pleuropneumoniae is a widely studied bacterium, however its pathogenesis is not yet fully understood. The prevalence of the 18 serotypes of A. pleuropneumoniae varies by geographic region, in North American area, more specifically in Mexico, serotypes 1, 3, 5b, and 7 show higher prevalence. Actinobacillus pleuropneumoniae is described as a strict extracellular pathogen with tropism for lower respiratory tract. However, this study depicts the ability of these serotypes to adhere to non-phagocytic cells, using an endothelial cell model, as well as their ability to internalize them, proposing it could be considered as an intracellular pathogen.

Immunoprotective Efficacy of Six In vivo-Induced Antigens against Actinobacillus pleuropneumoniae as Potential Vaccine Candidates in Murine Model

Six in vivo-induced (IVI) antigens—RnhB, GalU, GalT, Apl_1061, Apl_1166, and HflX were selected for a vaccine trial in a mouse model. The results showed that the IgG levels in each immune group was significantly higher than that of the negative control (P < 0.001). Except rRnhB group, proliferation of splenocytes was observed in all immunized groups and a relatively higher proliferation activity was observed in rGalU and rGalT groups (P < 0.05). In the rGalT vaccinated group, the proportion of CD4+ T cells in spleen was significant higher than that of negative control (P < 0.05). Moreover, proportions of CD4+ T cells in other vaccinated groups were all up-regulated to varying degrees. Up-regulation of both Th1 (IFN-γ, IL-2) and Th2 (IL-4) cytokines were detected. A survival rate of 87.5, 62.5, and 62.5% were obtained among rGalT, rAPL_1166, and rHflX group, respectively while the remaining three groups was only 25%. Histopathological analyses of lungs indicated that surviving animals from the vaccinated groups showed relatively normal pulmonary structure alveoli. These findings confirm that IVI antigens used as vaccine candidates provide partial protection against Actinobacillus pleuropneumoniae infection in a mouse model, which could be used as potential vaccine candidates in piglets.

Genomic and antigenic characterization of monomeric autotransporters of Haemophilus parasuis: an ongoing process of reductive evolution

The genome of the highly pathogenic Haemophilus parasuis Nagasaki strain (serovar 5) was sequenced to 99 % completion. A genomic comparison with two other pathogenic serovar 5 H. parasuis strains identified six genes per genome (bmaA1-bmaA6) encoding β-barrel monomeric autotransporters, bmaA2 and bmaA3 being pseudogenes in at least one strain. The remaining encoded proteins were predicted to belong to the subtilisin (BmaA1 and BmaA4) and cysteine (BmaA5 and BmaA6) protease families. Allelic polymorphism was detected in other H. parasuis strains by comparative genomic hybridization using microarrays. Recombination events were observed, some of them leading to gene disruption in one of the three strains, although synteny around bmaA genes was conserved. These results suggest that bmaA genes are undergoing a process of reductive evolution. To evaluate their use as potential vaccine antigens, the products of the passenger domains of bmaA1, bmaA4, bmaA5 and bmaA6 were produced in Escherichia coli as recombinant proteins. They were detected by immunoblotting using sera of colostrum-deprived piglets recovering from a sublethal infection with H. parasuis (Nagasaki). The existence of specific antibodies after infection with H. parasuis also demonstrated in vivo expression. Using proteomics, only BmaA6 was detected in the in vitro-grown Nagasaki strain. Interestingly, the translocator domain was found in the outer membrane, while the passenger domain was located in supernatants. These results indicate that BmaA proteins could be considered as immunogen candidates to improve H. parasuis vaccines. However, their capacity to confer protective immunity needs to be studied further.