Defensins and innate host defence of the gastrointestinal tract

Abstract

A continuous microbial threat is also posed by a wide array of colonising microbes throughout the gut, with especially large numbers in the mouth and colon. Infectious complications that often follow treatment with antibiotics suggest that colonising symbionts contribute to host defence against pathogens. Yet, in the absence of effective defence mechanisms, even symbiotic microbes can multiply rapidly and overwhelm the mammalian host. Despite the presence of microbes, normal digestive tract surfaces generally show little evidence of inflammation, the coordinated pattern of vasodilatation, leucocyte recruitment and transudation of leucocytes and plasma that constitutes a common response of many tissues to microbes. In the absence of inflammation, steady state defence in this organ system must rely on other broadly effective mechanisms. This review will focus on one such mechanism, the production of defensins, a group of antimicrobial peptides that contribute to innate immune defences in the gastrointestinal tract and other body surfaces.