The epitope structure in lipopolysaccharide recognized by the serotype 2-specific monoclonal antibody of Actinobacillus pleuropneumoniae.

The polysaccharide structure recognized by a monoclonal antibody specific to serotype 2 lipopolysaccharide of Actinobacillus pleuropneumoniae was investigated using an enzyme-linked immunosorbent assay inhibition test. Lipopolysaccharide obtained from serotype 2, strain SH-15, was hydrolysed with acetic acid to liberate the polysaccharide portion, and the polysaccharide mixture was fractionated by gel filtration. The longer polysaccharide, composed of O-antigenic polysaccharide and core, fully inhibited the binding of monoclonal antibodies to a whole cell antigen of strain SH-15, whereas the core oligosaccharide without O-polysaccharide did not. No inhibition was observed with the monosaccharides which were the components of serotype 2 LPS. Enzyme-linked immunosorbent assay inhibition ability of O-polysaccharide was completely lost only by O-deacetylation. These results demonstrate that the epitope of the serotype-specific monoclonal antibody resided in O-polysaccharide of LPS and that the O-acetyl group was essential for the epitope structure.