Salmonellosis in Mice Infected with Mycobacterium bovis BCG II. Resistance to Infection

Mycobacterium bovis BCG-infected mice were found to be consistently more resistant than normal mice to superinfection with Salmonella typhimurium. This resistance was manifested by a decreased mortality and by a decrease in the number of viable Salmonella in the BCG mice 3 to 4 days after challenge. Antibody production, as determined in the serum by the complement-dependent bactericidal system or in the spleen by the Jerne plaque technique, was either equivalent to or less than that of normal mice. Therefore, the immunity to S. typhimurium possessed by BCG-infected mice cannot be the expression of a greater or more rapid antibody response. By exclusion, these findings appear to support the concept of "cellular immunity."