Book Chapter, Chapter 7
According to hygiene hypothesis, diseases of the immune system are increasing with socio-economic and sanitary conditions. This is evidenced by high incidences of allergic and autoimmune diseases in Western countries than in developing countries. The underlying factor is disruption of normal microbiota and their associated beneficial effects on intestinal mucosal immunity. Thus the pathogeneses of these disorders appear to revolve around impaired ability of the intestinal microbiota to effectively modulate and thus balance the body immune responses. As a result the immune system reacts excessively to antigens that would otherwise be tolerated and thus results in allergic reactions. Alternatively, the immune system reacts to self-antigens to cause autoimmune diseases. Some of these disorders are characterized by persistent production of inflammatory mediators leading to chronic inflammation and tissue damage. Several reports have indicated that oral administration of excessive numbers of selected members of microbiota, so called probiotic bacteria, prevents, treats, and improves the conditions of patients with immune-mediated disorders like allergy, inflammatory bowel diseases, and type 1 diabetes mellitus. Current knowledge suggests that probiotic bacteria mediate their beneficial effects via modulation of the immune system to balance its responses and institute protection. Herein the knowledge of new research on the role of probiotic bacteria on the development of some of the immune mediated diseases is reviewed in order to provide an insight in the role of probiotics in health and disease.