Abstract
BackgroundActinobacillus pleuropneumoniae, the causative bacterial agent of porcine pleuropneumonia, produces Apx toxins which belong to RTX toxin family and are recognized as the major virulence factors. So far, their target receptor(s) has not been identified and the disease cytopathogenesis remains poorly understood. Production of an active Apx toxin and characterization of its toxic activity constitute the premises necessary to the description of its interaction with a potential receptor. From this point of view, we produced an active recombinant ApxIIIA toxin in order to characterize its toxicity on peripheral blood mononucleated cells (PBMCs) isolated from several species.FindingsToxin preparation exercises a strong cytotoxic action on porcine PBMCs which is directly related to recombinant ApxIIIA since preincubation with polymyxin B does not modify the cytotoxicity rate while preincubation with a monospecific polyclonal antiserum directed against ApxIIIA does. The cell death process triggered by ApxIIIA is extremely fast, the maximum rate of toxicity being already reached after 20 minutes of incubation. Moreover, ApxIIIA cytotoxicity is species-specific because llama, human, dog, rat and mouse PBMCs are resistant. Interestingly, bovine and caprine PBMCs are slightly sensitive to ApxIIIA toxin too. Finally, ApxIIIA cytotoxicity is cell type-specific as porcine epithelial cells are resistant.ConclusionWe have produced an active recombinant ApxIIIA toxin and characterized its specific cytotoxicity on porcine PBMCs which will allow us to get new insights on porcine pleuropneumonia pathogenesis in the future.
Highlights
Actinobacillus pleuropneumoniae, the causative bacterial agent of porcine pleuropneumonia, produces Actinobacillus pleuropneumoniae repeats in toxin (RTX) toxin (Apx) toxins which belong to RTX toxin family and are recognized as the major virulence factors
Contrary to LtxA (Aggegatibacter actinomycetemcomitans), LktA (Mannheimia haemolytica), HlyA (Escherichia coli) and CyaA (Bordetella pertussis) RTX toxins for which it was shown that they acted through β2-integrin receptors to induce a cytotoxic effect on leukocytes [1118], the target receptor of pore-forming toxin (PFT) Actinobacillus pleuropneumoniae RTX toxin (Apx) toxins has not been identified yet and cytopathogenesis of associated disease remains poorly understood
Anti-porcine (Po) CD18 mAb bound near 100% of P1 cells (Fig. 1B), confirming that it corresponds to the porcine peripheral blood mononucleated cells (PBMC) population
Summary
Actinobacillus pleuropneumoniae is the bacterial causative agent of porcine pleuropneumonia, a frequent and highly infectious disease generating significant economic losses related to deficits in zootechnical profits and intensive use of antibiotics [1,2]. Contrary to LtxA (Aggegatibacter actinomycetemcomitans), LktA (Mannheimia haemolytica), HlyA (Escherichia coli) and CyaA (Bordetella pertussis) RTX toxins for which it was shown that they acted through β2-integrin receptors to induce a cytotoxic effect on leukocytes [1118], the target receptor of PFT Apx toxins has not been identified yet and cytopathogenesis of associated disease remains poorly understood. In this perspective, active Apx toxin production and characterization of its toxic action constitute premises necessary to the description of its interaction with a potential receptor
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