Correlation between intestinal immune response to colonization factor antigen/I and acquired resistance to enterotoxigenic Escherichia coli diarrhea in an adult rabbit model.

Immunoprotection against diarrhea caused by colonization factor antigen/I (CFA/I)-positive, human-associated, enterotoxigenic Escherichia coli was investigated using the adult rabbit intestinal temporary ligation technique. An oral dose of 1 X 10(8) viable cells of enterotoxigenic Escherichia coli strain H-10407 (078:H11:CFA/I) produced diarrhea in all animals challenged. Rabbits allowed to survive this challenge dose were re-challenged approximately six weeks later with the result that four of seven (57%) did not develop diarrhea. Peroral immunization of rabbits with purified CFA/I elicited protection against challenge with strain H-10407; this protection was dose-related and CFA/I-specific. Immunoprotection did not correlate with a systemic antibody response. CFA/I produced a relatively poor immune response in terms of the number of IgM- and IgG-producing cells in the lamina propria of the animals but did elicit a vigorous increase in the number of intestinal IgA- and anti-CFA/I-producing cells. There was a highly significant inverse relationship between the number of IgA- and anti-CFA/I-producing cells in the lamina propria of the rabbits and the diarrhea response to the challenge strain H-10407 (correlation coefficients of -0.616 and -0.678 respectively). It is concluded that anti-CFA/I antibody, probably of the IgA class, is the major immune response to orally administered CFA/I and that this response is highly immunoprotective.