Immunity Provided by Colonized Enteric Bacteria

Floral organisms influence the host's immunological activities not only in the mucosal barrier system but also systemically. Using "unnatural" animals, i.e., monoassociated mice, we attempted to explore the stimulatory effect of intestinally colonized floral organisms. These gnotobiotic mice exhibited specific immune response against associated bacteria probably through the intestinal mucosal membrane. IgA antibody to the colonized bacteria was detected in the secretion. In addition, it was suggested that the specific response accompanied a production of IgA unrelated to the stimulating antigen. Cell mediated immunity to the colonized bacterial antigen could be detected by the footpad reaction as well as the macrophage migration inhibition test with peritoneal exudate cells after monoassociation. These findings suggest that non-specific resistance to invading microorganisms or other noxious agents may be operative through floral organisms in both mucosal and systemic fashions.