Development of Mucosal Immunity: Functional Interactions with Mucosal Microbiome in Health and Disease

The mucosal surfaces and the skin are the primary sites of interactions between the mammalian host and the external environment. These sites are exposed continuously to the diverse components of the environment, including subcellular, unicellular and multicellular organisms, dietary agents and food products; and numerous other soluble or cellular air or water borne products. The development of innate and adaptive immunity in the mucosal surfaces and the skin are the principal mechanism of mammalian defense evolved to date, in order to maintain effective homeostatic balance between the host and the external environment. The innate immune functions are mediated by a number of host specific Pathogen Recognition Receptors (PRR), designed to recognize unique Pathogen Associated Molecular Patterns (PAMP), essential to the molecular structure of the microorganism. The major components of specific adaptive immunity in the mucosal surfaces include the organized antigen-reactive lymphoid follicles in different inductive mucosal sites and the effector sites of the lamina propria and sub-epithelial regions, which contain lymphoid and plasma cells, derived by the homing of antigen sensitized cells from the inductive sites. The acquisition of environmental microbiome by the neonate in its mucosal surfaces and the skin, which begins before or immediately after birth, has been shown to play a critical and complex role in the development of mucosal immunity. This report provides an overview of the mammalian microbiome and highlights its role in the evolution and functional development of immunologic defenses in the mucosal surface under normal physiologic conditions and during infectious and non-infectious inflammatory pathologic states associated with altered microbiota.