ABSTRACT
A critical role(s) for the innate and adaptive immune system in maintaining mucosal homeostasis has become evident through the study of humans with naturally occurring primary immunodeficiencies that result from dominant mutations in immune-related genes, and of murine strains with similar genetically defined mutations. In order to highlight the specific roles of unique aspects of the mucosal immune system in maintaining mucosal homeostasis, this chapter focuses on those human immunodeficiencies where gastrointestinal manifestations usually occur. Immunoglobulin A deficiency is the most prevalent of the primary immunodeficiencies, affecting approximately 1 in 700 individuals of European ancestry and significantly fewer of those of Asian ancestry. Combined immunodeficiencies are those disorders that are genetically determined and lead to loss of both B- and T-cell function. The common presentation of mucosal and particularly gastrointestinal symptomatology in the setting of primary immunodeficiencies underscores the role of the immune system in regulating mucosal homeostasis.
