Gut Feeling
According to the hygiene hypothesis, reduced exposure to infections in early childhood – owing to diminishing family size and improvements in living standards and personal hygiene, for example – may increase the risk of allergic and autoimmune disease. This concept is supported by epidemiological and clinical reports documenting increased incidences of inflammatory bowel diseases, colon cancer, asthma, type 1 diabetes and multiple sclerosis over the past 50 years in societies with improved medical care and hygiene (for example, Europe, the United States and Japan) but not in undeveloped countries. However, the application of major interventions, including vaccination, sanitation, and antibacterial and antiviral therapies, often does not permit discrimination between infectious and non-infectious microorganisms and has undoubtedly led to changes in human association with the microbial world as a whole. The hygiene hypothesis does not address humanity’s primary relationship with bacteria: the harbouring of multitudes of microbial species during commensalism. A new study just published shows that symbiotic bacteria residing in the mammalian gastrointestinal tract produce molecules that mediate healthy immune responses and protect the host from inflammatory disease. The authors propose that the mammalian genome does not encode for all functions required for immunological development but rather that mammals depend on critical interactions with their microbiome (the collective genomes of the microbiota) for health.
A microbial symbiosis factor prevents intestinal inflammatory disease
Nature 453: 620-625, 29 May 2008
Humans are colonized by multitudes of commensal organisms representing members of five of the six kingdoms of life; however, our gastrointestinal tract provides residence to both beneficial and potentially pathogenic microorganisms. Imbalances in the composition of the bacterial microbiota, known as dysbiosis, are postulated to be a major factor in human disorders such as inflammatory bowel disease. We report here that the prominent human symbiont Bacteroides fragilis protects animals from experimental colitis induced by Helicobacter hepaticus, a commensal bacterium with pathogenic potential. This beneficial activity requires a single microbial molecule (polysaccharide A, PSA). In animals harbouring B. fragilis not expressing PSA, H. hepaticus colonization leads to disease and pro-inflammatory cytokine production in colonic tissues. Purified PSA administered to animals is required to suppress pro-inflammatory interleukin-17 production by intestinal immune cells and also inhibits in vitro reactions in cell cultures. Furthermore, PSA protects from inflammatory disease through a functional requirement for interleukin-10-producing CD4+ T cells. These results show that molecules of the bacterial microbiota can mediate the critical balance between health and disease. Harnessing the immunomodulatory capacity of symbiosis factors such as PSA might potentially provide therapeutics for human inflammatory disorders on the basis of entirely novel biological principles.
Related:
- The Hygiene Hypothesis
- Microbes on the skin: disease or defence?
- Probiotics – friendly bacteria?
- Good Germs, Bad Germs: Health and Survival in a Bacterial World
Tags: Antibiotics, Bacteria, Biology, Food, Health, Medicine, Microbiology, Science
