Protection of C3H/HeJ mice from lethal Salmonella typhimurium LT2 infection by immunization with lipopolysaccharide-lipid A-associated protein complexes

Abstract

C3H/HeJ mice were immunized intraperitoneally (i.p.) with lipopolysaccharide (LPS)-lipid A-associated protein (LAP) complexes or with purified protein-free LPS prior to lethal i.p. or intravenous Salmonella typhimurium LT2 challenge. Our results demonstrated that these Salmonella-hypersusceptible mice can be effectively protected against 1,000 100% lethal doses of S. typhimurium LT2 (i.e., 10,000 viable bacteria) administered by i.p. challenge and against 100 50% lethal doses of S. typhimurium LT2 (i.e., 1,000 viable bacteria) administered by intravenous challenge when previously immunized with LAP-LPS complexes. In contrast to these results, immunization with LPS afforded markedly less protection regardless of the route of challenge, thus suggesting that the LAP portion of LAP-LPS complexes may be necessary for inducing protection against Salmonella infections. For most experiments, antigens were emulsified in complete Freund adjuvant (CFA); however, the CFA portion of the vaccine was suggested not to be an essential comnponent for the induction of immunity to Salmonella infections, since equivalent levels of protection were obtained when it was omitted from the vaccine. The induction of immunity to murine salmonellosis by prior immunization with CFA-LAP-LPS was demonstrated not to be a transient phenomenon, since C3H/HeJ mice were still protected against lethal S. typhimurium LT2 challenge as late as 225 days postimmunization.

Determinants of immunity to murine salmonellosis: studies involving immunization with lipopolysaccharide-lipid A-associated protein complexes in C3H/HeJ mice

“…C3H/HeJ mice immunized with saline were afforded 0% survival when challenged with either Samonella strain. Immunization with LPS (04, 5) afforded mice 0% survival when challenged with the heterologous strain PL5 (09) and 40% survival when 45 challenged with the homologous strain PL8 (04, 5), results similar to those we have reported earlier [19]. Immunization with LAP-LPS (04, 5) significantly improves survival to challenge with the LPS-homologous PL 8 (04, 5) strain, also similar to what we have reported previously [19].…”

“…Immunization with LPS (04, 5) afforded mice 0% survival when challenged with the heterologous strain PL5 (09) and 40% survival when 45 challenged with the homologous strain PL8 (04, 5), results similar to those we have reported earlier [19]. Immunization with LAP-LPS (04, 5) significantly improves survival to challenge with the LPS-homologous PL 8 (04, 5) strain, also similar to what we have reported previously [19]. Interestingly, however, immunization with LAP-LPS (04, 5) provides some protection to challenge with the LPS-heterologous strain, PL5 (09) (Fig.…”

“…We have earlier reported that C3H/HeJ mice can be effectively protected against S. typhimurium LT2 infection by prior immunization with LAP-LPS complexes isolated from the outer membrane of this organism [19]. In the present study, we describe experiments designed to determine the relative contribution of humoral versus cellular immunity induced by this non-viable Salmonella vaccine.…”

“…LPS and LAP-LPS were isolated from S. typhimurium LT2 as previously described [19]. Briefly, S. typhimurium LT2 was grown in trypticase soy broth (BBL Microbiology Systems~ Cockeysville, MD) washed with sterile saline, and then extracted with butanol to yield LAP-LPS [20].…”

“…We have previously reported that Salmonellahypersusceptible C3H/HeJ mice can be protected to a significant extent against lethal S. typhimurium LT2 challenge by prior immunization with LAP-LPS complexes isolated from this bacterial strain. In contrast, immunization with LPS results in significantly reduced survival against Salmonella infection [19]. In order to determine the relevant antigen(s) necessary to induce immunity against lethal Salmonella challenge (i.e., LAP or LPS) we initially utilized 2 Salmonella strains, which differ in their O-antigen serotype, as the challenge strains.…”