Induction of immunologic memory by a lipopolysaccharide-protein complex isolated from Fusobacterium necrophorum: humoral response.

The serum antibody response in BALB/c mice to a lipopolysaccharide-protein (LPS-P) complex was monitored by the enzyme-linked immunosorbent assay, total and 2-mercaptoethanol-resistant hemagglutination, and radial immunodiffusion. Dose-response analyses demonstrated that suitable primary doses of LPS-P injected IV or IM induced substantial concentrautions of specific serum immunoglobulin (Ig) M and IgG. Moreover, these values were greatly enhanced with small-dose booster injections. Inoculation of mice with a suitable primary IM dose of aluminum hydroxide-precipitated LPS-P-induced specific IgM and IgG amounts that were detectable for 120 days. An enhanced secondary response to antigen booster injections was generated 105 days after primary inoculation, providing direct evidence that LPS-P can induce immunologic memory. Similar results were obtained for IV inoculations of LPS-P, although the primary IgG response was not as persistent. Seemingly, the memory response to LPS-P was largely dependent on the protein component of the molecule.