Immunobiology of the gastrointestinal tract.

The interplay between the gut and immune abnormality appears to be a logical extension of the thesis that secretory IgA is the major immunologic line of defense between the outside environment and the host. Thus immunologic deficiency, particularly of IgA and combined T- and B-lymphocyte abnormalites, profoundly influences gut integrity. Conversely, gut pathology is bound to interfere with immunologic function, so that both humoral and cellular immunity may be impaired. Finally, hypersensitivity phenomena in the gut, resulting in immune injury, may cause gastrointestinal disturbances. As better diagnostic tools have become available, more direct evidence of hypersensitivity immune injury has been described.