Gastrointestinal immunity in health and disease

The gastrointestinal lymphoid tissue (GALT) is under constant antigenic challenge from bacteria and food and must be able to distinguish between benign and pathogenic organisms. Recent advances in understanding the organization and function of GALT reveal how it is able to direct appropriate immune responses according to the nature of the antigen and how inappropriate immune responses can lead to local and systemic immunopathology and/or infection. The interaction of the normal bowel flora and GALT is critical to normal local and systemic immune function and plays a major role in the pathogenesis of some immune-related diseases. This review draws upon information from veterinary, human, and laboratory animal studies to provide an update of mechanisms and consequences of function and dysfunction in the gastrointestinal immune system.