Inhibition of adherence of Actinobacillus pleuropneumoniae to porcine respiratory tract cells by monoclonal antibodies directed against LPS and partial characterization of the LPS receptors

Actinobacillus pleuropneumoniae is the causative agent of porcine fibrinohe morrhagic necrotizing pleuropneumonia. We have previously identified the li popolysaccharides (LPS) as the major adhesin of A. pleuropneumoniae involve d in adherence to porcine respiratory tract cells. In the present study, ad herence of A. pleuropneumoniae to porcine tracheal frozen sections was inhi bited by homologous monovalent Fab fragments produced from monoclonal antib odies 5.1 G8F10 and 102-G02 directed, respectively, against the A. pleuropn eumoniae serotype I or serotype 2 O-antigens. These results confirm the imp ortant role played by LPS in adherence of A. pleuropneumoniae and suggest t hat these adhesins might represent good vaccine candidates. We also investi gated the presence of A. pleuropneumoniae receptors in tracheal cell prepar ations from piglets of four different breeds. Using Far-Western binding ass ays, we identified proteins recognized by whole cells of A. pleuropneumonia e reference strains for serotype 1 and 2, and local isolates belonging to t he same serotypes, and also recognized by extracted LPS from both reference strains. We confirmed the proteinaceous nature of these LPS-binding molecu les by their staining with Coomassie brilliant blue, sensitivity to protein ase K digestion, resistance to sodium m-periodate oxidation, and their inab ility to stain with glycoprotein-specific reagents. Four low-molecular mass bands (14-17 kDa) seemed to correspond to histones. We also identified pro teins at Mr 38,500 that could represent putative receptors for A. pleuropne umoniae LPS in swine respiratory tract cells.