Abstract
Maintenance of intestinal immune system homeostasis requires the host to distinguish commensal bacteria, which are members of the gut microbiota, from pathogenic micro-organisms and respond accordingly. Although the mechanisms that maintain this homeostasis are not completely understood, evidence, particularly from studies of rodents and humans, has enabled the unravelling of the finely tuned balance that exists between the host and its microbiota. Commensal bacteria, which are in close contact with cells of the intestinal immune system, have been shown to play an important role in regulation of innate and adaptive immune mechanisms. The anatomy of the gut-associated lymphoid tissue in avian and ruminant species differs from that of monogastric animal species. However, many of the mechanisms that are used to identify and respond to commensal bacteria are highly conserved among species and are, therefore, thought to function similarly. In recent years, interest in the area of gut microbiota interactions with the host immune system has significantly increased. This is partly because of the implications of these interactions for the development of novel strategies for improving gut health in animals.