ABSTRACT
The gut-associated lymphoid tissue (GALT) comprises the largest immune organ in the mammal and functions as part of both the adaptive and innate arms of the immune system. GALT is composed of several areas of organized secondary lymphoid architecture called Peyer's patches (PPs), isolated lymphoid follicles (ILFs), and mesenteric lymph nodes (MLNs), and these primarily function as inductor sites. Once antigen presenting cells (APCs) have interacted with naive lymphocytes in the PPs, ILFs, and MLNs, the now primed cells migrate through the periphery and other effector sites before the majority home to the lactase persistence (LP) and epithelium of the gut mucosa. Since the activation of naive lymphocytes appears to occur primarily in organized lymphoid tissues, and effector function usually occurs at distant peripheral sites, cell trafficking and migration are clearly an essential component of appropriate immune function. Oral tolerance describes the process by which active immune responses to orally administered antigen are suppressed.
