Modifications of the local immune response to Vibrio cholerate attributed to the intestinal microbial flora of the mouse.

Oral immunisation studies in germfree, specific pathogen-free (SPF) and conventionalised mice illustrated that the autochthonous gut flora can have a suppressive effect on the induction of a local intestinal immune response to Vibrio cholerae. Temporary colonisation of the small bowel by viable vibrios occurred only in the germfree animal. The lack of colonisation in SPF and conventionalised mice was presumably a cause of their lower coproantibody responses. Prevention of colonisation was probably due to bacterial antagonism rather than to cross-reaction antibodies. This conclusion was reinforced by studies involving oral immunisation of SPF mice maintained on streptomycin, and of conventionalised ex germfree mice. In addition to the increased protective coporantibody response of animals with reduced gut flora, there were increased levels of non-complement-fixing protective antibodies in their serum, which were probably derived from the guy lamina propria.