A gut reaction: Aging affect gut-associated immunity

Abstract

The digestive functions of the intestinal tract are familiar to everyone. The immunoprotective functions of the intestinal tract are not. Not long ago, when relatively little was known about the structure and function of the intestinal immune system, it was reasonable to conclude that aging affected gastrointestinal (GI) immunity to a minor extent, if at all. However, there were gerontologists who were not convinced because - given excessive functional potential beyond what is normally required - it was doubtful whether experiments involving whole animals or complex ex vivo systems were reliable. To illustrate the point, consider the following quotation1: "The multiorgan system that composes the gastrointestinal tract has a large reserve capacity, and thus there is little change in gastrointestinal function because of aging in the absence of disease." Although that quotation was directed at the digestive function of the GI system, it may reasonably be argued that it embraces the immunological function as well. We intend to develop that argument in this chapter. First, however, we will provide a review of current understanding and thinking about the elements of the gut-associated immune system. After that, we will attempt a perception, with the aid of Minerva and a little help from Bacchus, of the aspects or features of gut-associated lymphoid tissue (GALT) that are most in need of investigation: most likely to yield new insight. Finally, we will argue that the gradual decline with advancing age in overall competence of GALT reaches a point at which the reserve potential is largely exhausted; and at that point, the elderly evince infections, autoimmune disorders, and neoplasias associated with resident microorganisms that had remained latent. © Springer Science+Business Media, LLC 2009. All rights reserved.