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

The ability of a lipopolysaccharide protein (LPS-P) complex extracted from Fusobacterium necrophorum to establish immunologic memory in BALB/c mice splenocytes was demonstrated. The LPS-P molecule differed from the phenol water-extracted LPS because it contained approximately 12% protein. Initial experiments showed that primary and secondary spleen plaque-forming cell (PFC) responses to IV or IM injections of LPS-P were highly dose-dependent. Suitable primary doses stimulated significant (P less than 0.05) amounts of direct and direct + indirect PFC by postinoculation day (PID) 14 and primed the mice for an enhanced secondary response to small booster injections. When mice were inoculated with a suitable primary IM dose of aluminum hydroxide-precipitated LPS-P, significant amounts of direct and direct + indirect PFC were detectable through PID 120. Moreover, significant enhancement of these values was attained with an IV booster injection at PID 105. Primary IV inoculation with LPS-P produced similar results, although the primary response was not as persistent.