ABSTRACT
The primary role of the small intestine is the absorption of simple and complex nutrients. As such, the gut is exposed to a wide spectrum of foreign substances ranging from the noxious to those which are absolutely essential to the maintenance of good health, natural growth and development. The capacity of the normal small intestine to distinguish between innocuous substances that traverse its length from pathogenic, irritant or allergenic material is the consequence of precise homeostatic regulation, ensuring for the most part efficient digestive function and freedom from disease. Contact with antigenic material in the gastrointestinal tract, results in immunological responses which range from tolerance, at the one extreme, to complete protection at the other. In disease conditions, immunological effector mechanisms may be initiated following pathogen-induced injury to the integrity of the intestinal tissue. Such effector mechanisms appear to feature also in immune responses against a number of intestinal helminths. However, in man, it is often the case that ubiquitous gastro-intestinal helminthiases, while eliciting a range of inflammatory responses, appear to give rise to persistence of infection and/or immunological tolerance of the presence of parasites (Chapter 13).
