The Gut Associated Lymphoid Tissue as a Model of a Specialized Immune Subsystem

Abstract

It has been recognised for centuries that the gut of many animals is richly endowed with what we now describe as lympho/reticular tissue. It is agreed generally now that the primary function of such lympho/reticular tissue is to generate immune effector mechanisms which protect the body against the onslaughts of pathogenic bacteria, viruses and toxins. Because the gut is designed to absorb nutriment and has a vast surface area that is in contact with the outside world, it is more than usually at risk and requires special protection. The protection afforded to the gut by the gut associated lymphoid tissue (GALT) is by no means absolute; even in developed communities, which have sophisticated sanitary arrangements and medical supervision, occasional illness caused by enteric infections is by no means rare. In undeveloped communities, especially where population density is high such infections cause continual morbidity and mortality. The young of both man and animals are particularly at risk; the adaptation (in an immunological sense) to pathogenic and commensal bacterial flora necessarily takes time, and, in many species, the GALT is poorly developed at birth. During this process of adaptation the GALT very occasionally over reacts and produces antibodies and immunocytes directed at normal dietary constituents so that states of clinical hypersensitivity, or allergy, may develop.