Studies of immunogenicity of Westphal lipopolysaccharides from Pasteurella multocida in mice.

The immunogenicity of Westphal lipopolysaccharides (LPS) from 2 strains of Pasteurella multocida was tested in mice. When lipopolysaccharide from P. multocida strain P-1234 (bovine source) was inoculated into CF1 or $\text{C}\text{3}\text{H}\text{HeJ}$ mice, less than 20 per cent of the mice survived homologous challenge infection 4 weeks later. However, 90 per cent, or more, of the CF1 or $\text{C}\text{3}\text{H}\text{HeJ}$ mice survived homologous challenge infection after immunization with formolized P-1234 bacteria. Sera from the CF1 mice, but not $\text{C3H}\text{HeJ}$ mice, formed precipitin lines against P-1234 LPS in an agar gel diffusion test.Hyperimmune sera from rabbits inoculated with formolized P-1234 bacteria passively protected more than 80 per cent of the CF1 mice against challenge infection; however, sera from rabbits inoculated with P-1234 LPS or LPS adsorbed to sheep red blood cells protected less than 20 per cent of the challenged mice.Absorption of rabbit anti-whole cell sera with LPS slightly reduced the capacity of serum to passively protect mice against challenge exposure.