Chapter 18 - The Role of Mucosal Microbiota in the Development, Maintenance, and Pathologies of the Mucosal Immune System

Abstract

This chapter discusses the role of mucosal microbiota in the development, maintenance, and pathologies of the mucosal immune system. Most mucosal sites of lymphoid tissue—respiratory tract, adenoids, salivary glands, and urogenital tract—in healthy mammals are in a quiescent state and generally resemble the status of lymphoid areas in spleen and most peripheral lymph nodes (PLN). The intestinal tract, palatine tonsils, and occasionally the nasal-associated lymphoid tissue (NALT) are the exceptions. These mucosal lymphoid tissues are in a “physiologically normal state of inflammation.” The chapter focuses on how the intestinal microbes drive the development of gut-associated lymphoid tissue (GALT) during neonatal life and act to maintain its physiologically normal steady state of inflammation. Specific and adaptive, “natural” and semi-specific, and aspecific elements of the mucosal immune systems may benefit and be activated by host interactions with environmental antigens (Ags). To provide the experimental rationale for implicating intestinal or oral/nasal microflora in the development of GALT, palatine tonsil, and sometimes NALT and their steady state of inflammation, the chapter briefly contrasts the status of systemic lymphoid tissue in healthy mammals—spleen, PLN—with GALT, palatine tonsils, and NALT.