Structural and serological specificities of Pasteurella haemolytica lipopolysaccharides

Lipopolysaccharides (LPSs) from 16 serotypes of Pasteurella haemolytica were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and examined by silver staining and immunoblotting. Silver staining of proteinase K-digested cell lysates revealed two rough LPS serotypes (serotypes 2 and 8), which lacked demonstrable O-polysaccharide, while 14 others demonstrated a ladder pattern characteristic of smooth-type LPS. Purified LPSs from several serotypes yielded O-polysaccharide in addition to low-molecular-weight core oligosaccharide components when subjected to mild acid hydrolysis. Nuclear magnetic resonance spectroscopy revealed the O-chain polysaccharides of serotypes 1, 6, and 9 to be identical. Immunoblots using hyperimmune rabbit, mouse, bovine, and ovine sera from homologous and heterologous serotypes supported this finding and suggested that most of the A biotypes share common O-chain epitopes. Immunoblotting results also supported structural data which demonstrated that the O-polysaccharides of serotypes 3 and 15 and of serotypes 4 and 10 (T biotypes) are identical. Nuclear magnetic resonance analysis indicated that the core oligosaccharides of serotypes 1, 6, 8, 9, and 12 share similar structures, but that they are distinct from those of serotypes 3, 4, 10, and 15. Immunoblots with hyperimmune antisera and monoclonal antibody having specificity for the core region of serotype 1 LPS revealed shared epitopes in the core oligosaccharides of several A biotypes. Characterization of the molecular structure and antigenic specificities of LPS has been an important consideration in the development of purity and potency assays for veterinary vaccines which contain P. haemolytica.