Protective immunity in mouse salmonellosis: comparison of smooth and rough live and killed vaccines.

Protective immunity against Salmonella infection was studied in a mouse model. To study specificity of protection we used smooth (O-4,5,12) and rough vaccines; live and killed vaccines of both types were compared. The protection was assessed by enumerating the number of bacteria in the livers, and by following survival of the mice after intravenous challenge with smooth O-4,5,12 bacteria. Passively transferred antibodies induced by the smooth vaccines had a small protective effect and those induced by the rough vaccines no protective effect in this model. Both live vaccines induced long-lasting protective immunity which was much stronger than that mediated by antibodies. Since the live rough vaccine induced protective immunity and contained no O antigen we conclude that the protective immunity induced by it was mainly cell-mediated and directed to other antigens than the O antigen, the target of protective antibodies. Both killed vaccines also induced protective immunity, but this was weaker than that induced by the corresponding live vaccine.