The role of the colonic flora in maintaining a healthy large bowel mucosa.

This work explores the intricate relationships between bacterial products of fermentation, the short chain fatty acids and the effect that these have on the colonic epithelium and the immune system. It confirms that butyrate is a major energy source for the colonic epithelium and there may be a minor epithelial abnormality in the metabolism of butyrate in patients with ulcerative colitis. Immunological studies suggest that butyrate has an effect on lymphocyte activation and inhibits cell proliferation. Possibly, butyrate induces anergy in lymphocytes via an effect on the TCR receptor. This may represent a mechanism whereby colonic bacteria are able to regulate the host immune response. An abnormal response to butyrate may upset the homeostasis between the gut immune system and the colonising bacteria resulting in epithelial unrest and inflammation.