Acquired immunity against mouse typhoid: genetic restriction and comparative efficacy of ribosomal and conventional vaccines

Strains of mice immunised with a ribosomal preparation of Salmonella typhimurium varied in their ability to survive an intraperitoneal challenge of virulent S. typhimurium. Immunised nude (nu/nu), heterozygous (nu/+) mice, strain C57Bl/6J and strain CBA/J succumbed to lethal infection whereas strains C3D2F1/J, B6D2F1/J and A/J, and Swiss mice were fully protected. Strains DBA/2J and C3H/HeJ were partially protected. Enumeration of the systemic bacterial population after challenge with S. typhimurium indicated that all immunised mouse strains were able to reduce the infectious load. S. typhimurium was rapidly inactivated in the peritoneal cavity of immunised mice, effectively reducing the challenge and thereby limiting the number of organisms available to seed the systemic circulation. This response was also obtained in immunised athymic mice and was therefore attributed to a T-cell independent antibody response. Organisms that escaped destruction in the peritoneal cavity multiplied rapidly in the reticuloendothelial organs. Only mice from strains genetically capable of developing an effective cell-mediated immune response to the antigenic stimulus provided by the challenge organism itself survived infection. The efficacy of ribosomal immunisation was compared with immunisation by heat-killed bacteria, viable attenuated and viable virulent organisms by enumeration of the systemic bacterial population after intravenous challenge with S. typhimurium. Vaccination with ribosomal preparations or heat-killed organisms provided limited protection whereas immunity provided by viable organisms was far superior.