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An immunogenic, high molecular weight lipopolysaccharide (LPS)-protein complex isolated from a potassium thioncyanate extract of a Pasteurella multocida (P multocida ; strain P-2383, capsular type A and somatic type 3) was characterized. Chemical analysis of the complex by gas chromatography on a capillary column demonstrated that this complex contained most of the chemical constituents characteristic of LPS extracted by the phenol-water methed from the whole bacterium. However, there was proportionately more carbohydrate than fatty acid in the complex in contrast to LPS in which fatty acid seemed to be in excess. When toxicity of the complex was evaluated in 10-day-old chicken embryos, the complex was less toxic (LI)_(50)=12.72㎍) than the purified LPS (LD_(50)=0.44㎍). The LD_(50), of the LPS moiety extracted from the complex was 5.24㎍. Composition of the complex was analyzed by SDS-PAGE with silver staining and Western immunoblotting. The complex did not migrate through the polyacrylamide gel unless dissociated with SDS. The complex dissociated with SDS contained at least 32 different protein and polysaccharide components: 18 components reacted with ar antiserum against the complex. There was no significant compositional variation between the complexes, from different strains, but quantitative differences in individual components were noted. When cross-protectivity of the complex was evaluated in mice, this complex provided substantial protection not only against the homologous bacteriun but also against different P multocida strains of the same serotype. LPS-protein complexes isolated by the same method from other strains also induced protection against an challenge with P-2383.
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