Opsonic monoclonal antibodies against lipopolysaccharide (LPS) antigens of Pasteurella multocida and the role of LPS in immunity.

A panel of six monoclonal antibodies (MAbs) produced from mice immunized with Pasteurella multocida (M1404) (Heddleston serotype 2) reacted with homologous lipopolysaccharide, as indicated by enzyme immunoassay and immunoblotting. All six MAbs reacted with serotypes 2 and 5 of the 16 Heddleston serotypes. The reactive epitopes were localized on the bacterial cell surface by immunogold labelling. The antibodies could agglutinate P. multocida only if cells were first treated with 1 N HCl. All six MAbs opsonized P. multocida for phagocytosis by mouse macrophages but were not bactericidal in the presence of complement. They afforded only partial protection against infection in mice. The results, together with those of active immunization experiments with LPS, suggest a subordinate role for LPS in protection from experimental infection in mice.