STUDIES ON THE IMMUNITY OF EXPERIMENTAL TYPHOID

Abstract

Effects of the immunization with killed vaccines against the infection of mice with a virulent strain of S. enteritidis have been studied, special attention being given to analysing the infection into two categories, the large inoculum infection and the small inoculum infection.Prolongation in the survival time of animals, which indicates the protection against the primary septicemia caused by the large inoculum, was clearly demonstrated by the active immunization with killed vaccines prepared from culture types of salmonella which possess O antigens common to the challenge strain. Effects of the passive immunization against the large inoculum infection was observed in a similar result as in the active one, but to a lesser degree even though the pooled serum of immunized mice were used as the immunizing agent.The active immunization with a large amount of killed vaccines against the small inoculum infection (the typhoid and the secondary septicemia) was found somewhat effective, but there was no correlation between the effectiveness and the presence of O antibodies in the serum of immunized mice or of O antigens in culture strains used as the vaccine. No production of O antibodies for the challenge strain was noted at an early stage of the infection in the serum of mice immunized with a heterologous vaccine.All of T. T. T. (Hosoya), chrome vaccine (Ando), water-in-oil vaccine (Freund), and alum-vaccine showed no better immunizing effect against the small or large inoculum infections than the heat-killed vaccine.The seemingly “non-specific” immunity observed in the small inoculum infection was noted, though to a far lower degree, even in the large inoculum infection.Possibilities of the elucidation about this problem, taking the results of the past investigations with live vaccines into consideration, or in the connection with the immunity in other host-parasite systems, are discussed.