Oral Immunization in Experimental Salmonellosis II. Characteristics of the Immune Response to Temperature-Sensitive Mutants Given by Oral and Parenteral Routes.

A temperature-sensitive mutant of Salmonella enteritidis, selected because of its inability to proliferate normally at 37 C, has been used as a living vaccine in mice. When given parenterally or orally, it confers a high degree of resistance against otherwise lethal S. enteritidis infections given intraperitoneally or by mouth. In contrast to most other effective living Salmonella vaccines, the temperature-sensitive mutant survives for only short periods in mouse tissues. Although the vaccine provides protection against S. typhimurium infection, possibly because of antigenic relationships between the immunizing and challenge organisms, it is ineffective against the intracellular infection caused by Listeria monocytogenes. A study of the kinetics of S. enteritidis infection in the liver and spleen of normal and immunized mice has suggested that immunity is dependent upon development of a secondary immunological response which arises approximately 7 days after introduction of the challenge infection. Although humoral antibody production forms part of this secondary response, it is not necessarily responsible for control of the infection.