Microbial factors in chronic intestinal inflammation

This review summarizes recent investigations of microbial influences in ulcerative colitis, Crohn's disease, and experimental intestinal inflammation in rodents, Current data do not suggest that a specific persistent infection causes Crohn's disease but indicate that resident (normal) luminal bacteria induce chronic intestinal and systemic inflammation in genetically susceptible hosts. Anaerobic bacteria and bacterial products appear to be dominant stimulants in Crohn's disease and experimental colitis, whereas functionally abnormal aerobes may be involved in ulcerative colitis. Viable bacteria secondarily invade ulcerated mucosa, and enhanced uptake of bacterial cell wall polymers, chemotactic molecules, and antigens across the inflamed mucosa activate lamina propria inflammatory cells to perpetuate local inflammation. Systemic distribution of bacterial constituents leads to extraintestinal manifestations, The delicate balance between luminal microbial constituents and protective mucosal forces can be disturbed by genetically determined immunoregulatory abnormalities and environmental triggers, leading to chronic, relapsing intestinal inflammation.