The immunology and molecular biology of the gut-associated immune system.

Certain recent developments (since previous reviews) concerning the chemistry and mechanisms of transport of IgA antibodies will be reported. However, the major theme of the review will involve the morphological and functional characteristics of the cells found in mucosal tissues. Particular emphasis will be given to the gastrointestinal tract since considerably more data are available for this organ. The proposed mechanism by which antigen is processed in mucosal lymphoid tissues will be reviewed, including data pertinent to the commitment of the mucosal lymphocytes to IgA production. Emphasis will also be placed on cell migration patterns from the lymphoid tissues of the gut and lungs to other distal sites. The biological and medical implications, particularly in regard to immunizations at one site giving rise to immunity at distal sites, will be discussed in detail. The proposed mechanisms and significance of orally induced tolerance will also be reviewed.