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.
Immunology: The Neuronal Pathway to Mucosal Immunity
