HIGH-MOLECULAR-MASS LIPOPOLYSACCHARIDES ARE INVOLVED IN ACTINOBACILLUS-PLEUROPNEUMONIAE ADHERENCE TO PORCINE RESPIRATORY-TRACT CELLS

Actinobacillus pleuropneumoniae is the causative agent of porcine pleu ropneumonia. The major adhesin of A. pleuropneumoniae has been identif ied as the lipopolysaccharides (LPSs) (M. Belanger, D. Dubreuil, J. Ha rel, C. Girard, and M. Jacques, Infect. Immun. 58:3523-3530, 1990). Us ing immunoelectron microscopy and flow cytometry, we showed in the pre sent study that LPSs were well exposed at the surface of this encapsul ated microorganism. Immunolocalization with porcine lung and tracheal frozen sections showed that extracted LPS bound to the lung mesenchyme and vascular endothelium and to the tracheal epithelium, respectively . Inhibition of adherence of A. pleuropneumoniae with extracted LPS wa s also performed with lung and tracheal frozen sections. Acid hydrolys is of LPS revealed that the active component of LPS was not lipid A bu t the polysaccharides. LPSs from A. pleuropneumoniae serotypes 1 and 2 were separated by chromatography on Sephacryl S-300 SF, in the presen ce of sodium deoxycholate, according to their molecular masses. The ad herence-inhibitory activity was found in the high-molecular-mass fract ions. These high-molecular-mass fractions contained 2-keto-3-deoxyoctu losonic acid and neutral sugars, and they were recognized by a monoclo nal antibody directed against A. pleuropneumoniae O antigen but not re cognized by a monoclonal antibody against capsular antigen.