IMMUNE-RESPONSES TO NOVEL ESCHERICHIA-COLI AND SALMONELLA-TYPHIMURIUMVECTORS THAT EXPRESS COLONIZATION FACTOR ANTIGEN-I (CFA I) OF ENTEROTOXIGENIC ESCHERICHIA-COLI IN THE ABSENCE OF THE CFA/I POSITIVE REGULATOR CFAR/

An asd-stabilized plasmid carrying enterotoxigenic Escherichia coli cf aABCE genes was constructed and called pJGX15C-asd(+). Expression of c olonization factor antigen I (CFA/I) by this plasmid occurs independen tly of the cfaABCE positive regulator cfaR in attenuated Salmonella De lta aro Delta asd strain H683 and nonpathogenic laboratory E. coli asd strain chi 6212. Oral immunization of mice with nonpathogenic E. coli chi 6212 (pJGX15C-asd(+)) does not elicit significant serum or mucosa l responses against CFA/I. In contrast, oral immunization with a singl e dose of attenuated S. typhimurium H683(pJGX15C-asd(+)) elicits a 10( 5)-fold increase in CFA/I-specific serum immunoglobulin G and signific ant elevation of CFA/I-specific immunoglobulin A-secreting B cells in the lamina propria, mesenteric lymph nodes, and spleen. Thus, only the Salmonella-CFA/I construct effectively delivered CFA/I to the inducti ve sites of the gut-associated and systemic lymphoid tissues.