Protection of mice against Salmonella typhimurium with an O-specific polysaccharide-protein conjugate vaccine

Abstract

Serious infections with salmonellae remain a threat in many human populations. Despite extensive study of salmonella infections in animals and clinical experience with killed cellular vaccines, there are no vaccines against serotypes other than Sabnonella typhi licensed for human use. Serum antibodies to the 0-specific polysaccharide (O-SP) of salmonellae protect mice against invasive infection. In order to render it immunogenic, we have conjugated the O-SP of Sabnonella typhimurium to carrier proteins by various schemes. O-SP conjugated to tetanus toxoid (0-SP-TT) elicited antibodies in outbred mice after three subcutaneous injections without adjuvant. The O-SP alone elicited no detectable antibody. The antibody response to O-SP-TT was boosted by successive doses and consisted of immunoglobulin G (IgG) and IgM. Most mice only produced antibodies specific for the abequose (0:4 factor) region of the O-SP. Occasional animals also produced antibodies to the core oligosaccharide. Immunized mice were protected against intraperitoneal challenge with S. typhimurium, demonstrating a 160-fold increase in the 50% lethal dose. Passive immunization with conjugate-induced IgM or IgG also protected against challenge. These results indicate that an O-SP-TT conjugate, when given by a route and formulation acceptable for human use, protects mice agalnst challenge with S. typhimurium.

Synthesis, characterization, and immunological properties in mice of conjugates composed of detoxified lipopolysaccharide of Salmonella paratyphi A bound to tetanus toxoid with emphasis on the role of O acetyls

“…The surface polysaccharide of S. paratyphi A alone is not immunogenic in mice, most likely because of its comparatively low M r (51,66). There is experimental evidence that serum antibodies to the O-specific polysaccharides of group B and D salmonellae, whether actively induced or passively administered, confer protection to mice (12,16,55,56,63,72). The failure of bacterial vaccines, such as TAB, to confer protection against group A and B salmonellae may be likened to the failure of parenterally injected inactivated gram-negative bacteria to induce high lev- (6,18,56,61).…”

“…LPS. LPS was purified from S. paratyphi A as described elsewhere (15,38,72,74). Briefly, formalin-inactivated cells (200 g) were washed twice in PFS, suspended in PFW, and mixed with an equal volume of 90% phenol at 68ЊC for 30 min.…”

“…Serogroups were identified by agglutination with grouping antiserum and were confirmed by the Laboratory of Microbiology, Clinical Center, National Institutes of Health.LPS. LPS was purified from S. paratyphi A as described elsewhere (15,38,72,74). Briefly, formalin-inactivated cells (200 g) were washed twice in PFS, suspended in PFW, and mixed with an equal volume of 90% phenol at 68ЊC for 30 min.…”

“…In this study, the S. paratyphi A LPS was detoxified by treatment with acetic acid (O-SP) (15,38,72,74) or with hydrazine (DeALPS) (26,38,65) and was bound to tetanus toxoid (TT) (15,38,57,68,72). The immunogenicity in mice and bactericidal activities of antibodies elicited by these conjugates and the importance of O acetyls are examined.…”

“…Method 1 was as follows. O-SP and DeALPS were derivatized with ADH as described elsewhere (15,38,57,72). Polysaccharide (5 mg/ml in PFS) was brought to pH 10.5 to 11 with 0.1 M NaOH, and an equal amount of CNBr (1 g/ml of acetonitrile) was added.…”