抄録
Groups of cynomolgus monkeys were repeatedly administered with Shigella flexneri 2a by the oral route. Two to 4 times repetitions of administration with 20 mg (wet weight) of the virulent strain 5503 at intervals of 2-4 months resulted in a gradual decrease in the morbidity rate of clinical dysentery, while neither the same doses of avirulent variants derived from strain 5503 nor 0.01 mg of the virulent strain could protect animals against the subsequent oral challenge with 20 mg of virulent bacilli. Thus, cynomolgus monkeys can be regarded as having acquired an enhanced resistance to dysentery for at least 2-4 months after the infection with massive doses of virulent S. flexneri 2a. After 7-10 months, however, the enhanced resistance to Shigella infection was reduced. An average serum agglutinin titer before each experimental infection was about equal between dysenteric cases and non-dysenteric cases. Both dysenteric and non-dysenteric cases responded similarly to the challenge with a rise in serum antibody. But analyses of fluctuation of agglutinin titers suggest that this antibody is not responsible directly for the protection against dysentery infection in monkeys, therefore the titer can not be regarded as a measure for the estimation of magnitude of resistance to dysentery.
