The largest collection of lymphatic tissue in the human body is in the human gastrointestinal system. This makes the gut not only a digestive organ but also a large and essential component of the immune system.  The gut and immune system have an important link that works in both directions – diseases of the immune system can lead to GI dysfunction and alterations in the gut can lead to immunologic diseases.

“The gastrointestinal tract is a major site of disease in HIV infection, and is a good indicator of complications.”

A gut feeling

The gastrointestinal tract is a major site of disease in HIV infection, and is a good indicator of complications.  This can manifest itself as diarrhea and weight loss due to opportunistic infections, neoplasms of the GI system such as lymphomas or direct damage to gut tissue by HIV, termed HIV enteropathy. In the setting of highly active antiretroviral therapy, prolonged survival has led to a greater emphasis on managing chronic gastrointestinal symptoms with an eye towards both limiting symptoms and maintaining patient weight while always wary of more serious underlying causes.

Alternatively, disruptions of the gut can lead to immune system problems.  There is some suggestion that alterations in the gut microbiome can result in immunological dysregulation that may underlie disorders such as inflammatory bowel disease. Perhaps the mammalian immune system which appears designed to control microbes is, in fact, controlled by the microbes themselves.

Digestive health

Mammals take advantage of this gut-immunity link to protect newborns against infections.  When a nursing mother is exposed to a gut infection, antibodies to that disease are concentrated in colostrum and breastmilk.  These antibodies are transmitted to the breastfeeding infant in colostrum and breast milk and are then are available to the infant for protection against these diseases. Colostrum has been evaluated as a tool for reducing HIV-associated diarrhea.