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The gastrointestinal tract is a major component of the human immune system with a total lymphoid mass which is comparable with bone marrow.1 The Peyer’s patches are the principal sites of interaction among luminal antigens and lymphocytes, while the scattered lymphocytes in the lamina propria and epithelium are the effector cells that mediate immune response.2 The gut is also a site of synthesis and release of a specialised form of immunoglobulin A (secretory IgA) which is resistant to digestion. These immunological mechanisms are important because the gut has a huge surface area which interacts with the numerous potentially noxious agents including micro-organisms and dietary antigens.2 3 The intestinal tract is also one of the most metabolically active tissues in the body, with mucosal renewal taking place every three to five days, it is not surprising therefore that the gut is often the target organ for pathological processes in the immunosuppressed patients.4 5 The deleterious effects of immunosuppression on the integral functioning of the gut are assuming greater importance now that the use of potent long term immunosuppression has become widespread, for example in autoimmune diseases and organ transplantation.
Pathophysiology of immunosuppression on gastrointestinal function
The effects of immunosuppression on the gastrointestinal tract are multiple and include loss of gastric acidity, impaired immune response, reduced mucosal integrity, and compromised mucosal regeneration.
THE SUPPRESSION OF GASTRIC ACID SECRETION
This may be induced by treatment with H2 blockers or be secondary to malnutrition or immaturity (as in neonates), and the number of viable organisms surviving passage through the stomach can therefore increase by a 1000-fold causing gastroenteritis.
THE IMMUNE RESPONSE
The immune response may be globally attenuated by drugs such as steroids (reduction in chemotaxis and kinin production), or more specifically by cyclosporin A and tacrolimus, which inhibit T lymphocyte proliferation by inhibiting expression of interleukin 2.6 Such immunosuppression may cause persistence …
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