Protective Effect of Oral Salmonella enteritidis 11RX Infection against Colon Tumor Induction by 1,2-Dimethylhydrazine in Mic&

in vitro (3). After the carrier state has ended (about 40 days after infection) and resistance to tumor challenge has declined, the latter can be †̃ †̃recalled' â€b̃y injection of i i RX protein antigen at the site of tumor challenge (4, 6). Activated macrophages have been suggested (e.g. , Ref. i) to have a function in immune surveillance against neoplasia. Since S. enteritidis combines the properties of a natural entenic pathogen and the ability to bring about macrophage activation, it seemed a particularly suitable organism to test for a protective effect against colon tumor induction. The experiments reported here demonstrate that repeated p.o. challenge with live S. enteritidis 11RX during the course of DMH administration sig nificantly and reproducibly reduced the incidence and/on ex tent of colonic tumors in 2 strains of mice.