The normal colonization of the mammalian intestine with commensal microbes is
hypothesized to drive the development of the humoral and cellular mucosal immune
systems during neonatal life and to maintain the physiologically normal steady state of
inflammation in the gut throughout life. Neonatal conventionally reared mice and germ-free,
deliberately colonized adult mice (gnotobiotic mice) were used to examine the efficacy of
certain intestinal microbes.