The relationship between intestinal flora and the immunity of the intestinal tract

Summary: Mechanisms of immune protection in the intestinal tract provide for a wide range of investigation of intriguing complexity. In farm animal species, research has advanced from a position of almost exclusive concern with colostrum uptake to one of detailed examination of cellular activities. Thus, the underlying mechanisms of immune protection of the young, whether mediated passively through maternal antibody, or actively through the gut mucosal response in the developing offspring, have consistent features regarding uptake of antigen from the lumen, the isotypes of immunoglobuli n favoured in the gut and the effector mechanisms for protecting the mucosal surface. The origin of immune progenitor cells, when available for antigen-driven proliferation and migration, is discussed. Certain features of the gut-mammary axis in mucosal immunity link active and passive immunity, and suggest novel approaches to immunisation. The ontogeny of the gut immune response, the characteristics of localisation of immunocytes within the lamina propria and their population dynamics in affording antibody for the intestinal lumen have implications for development of oral vaccines for young animals. Finally, some unique characteristics of mucosal antibodies which influence microbial virulence have major implications for herd health, the farm environment and the human food chain.