Factors affecting the ability of various strains of Enterobacteriaceae to induce tumour resistance in mice.

Primary infection of mice with Salmonella enteritidis 11RX (11RX) confers resistance to challenge with 10(4) LD50 doses of Ehrlich Ascites tumour (EAT). A lipopolysaccharide-free protein extract of 11RX is capable of eliciting delayed type hypersensitivity (DTH) reactions in these mice and of "recalling" tumour resistance in long-term 11RX immunised mice, which no longer exhibit any resistance to tumour challenge. In the present study, we have examined the ability of five other strains of Enterobacteriaceae to induce similar effects. Primary i.p. injection of S. chester, S. luton or S. typhimurium G30 into mice resulted in persisting infections and the induction of peritoneal exudate cells (PEC) which were tumouricidal in vitro. DTH reactions could also be elicited in these animals with protein extracts of the homologous or the 11RX strain of salmonella. S. friedenan and E. coli K12, which did not persist in mice, did not elicit tumouricidal PEC and did not sensitize mice for DTH reactions. However, protein extracts from all the five strains could elicit tumouricidal PEC and DTH reactions in long-term 11RX-immunised mice (but not in normal mice). The results imply that a wide range of Enterobacteriaceae may possess antigen(s) which can be involved in tumour resistance, provided that these antigen(s) are presented in such a way that a cellular immune response develops.