Bactericidal Properties of Gastric Juice

Non-immunological defence mechanisms represent an important line of intestinal defence in addition to humoral and cellular immunity. This review summarises the evidence for the role of the non-immunological defence system. Protective factors that have been amply documented are gastric juice, intestinal motility, and intestinal flora. Components of pancreatic juice, lysozyme, and epithelial cell turnover may also be involved. Special attention is given to gastric acid, infection with Helicobacter pylon, and hypochlorhydria and their association with infectious diarrhoea. Epidemic hypochlorhydria is discussed since this increases sensitivity to intestinal infections in third world countries. TABLE I Nonimmunological defence mechanisms Gastric acid Intestinal motility Intestinal microflora Lysozyme Pancreatic secretions Bile Medical Department, Kantonsspital Liestal, University of Basel, 4410 Liestal, Switzerland S A Sarker K Gyr Correspondence to: Professor K Gyr, Medical Department, Kantonsspital Liestal, University of Basel, 4410 Liestal, Switzerland. Accepted for publication 8 October 1991 It is generally accepted that humoral and cellular immunity plays a key role in the defence mechanisms of the gut. In addition, the nonimmunological defence system (Table I) represents an important and often first line of defence. It probably affords sufficient protection, at least in people living in developed countries with good hygiene. This could explain observations that infectious bacterial disorders of the gastrointestinal tract are not more frequently observed in patients with humoral and cell mediated immune deficiency.' In some instances, patients totally lacking secretory immunoglobulins maintain a perfectly functioning gut.2 The acidity of the stomach, the motility of the intestine, the antibacterial effects of pancreatic enzymes,3'the normal intestinal flora, lysozyme,6 and the intestinal secretions are all effective antimicrobial factors that contribute to the non-specific host defence system. Furthermore, normal epithelial cell turnover and intestinal motility act together to purge the intestinal tract of harmful micro-organisms. Changes in the non-immunological defence factors can lead to increased susceptibility of the host to infections. For example, cholera and salmonella infections are more common in achlorhydric patients,78 and slowing down the intestinal motility with belladonna alkaloids prolongs symptomatic shigellosis.9