Skin microbiome regulates immune response. Implications for triclosan decision?

Naik S, Bouladoux N, Wilhelm C, Molloy MJ, Salcedo R, Kastenmuller W, et al. Compartmentalized Control of Skin Immunity by Resident Commensals. Science. 2012. doi: 10.1126/science.1225152 (not open access)

Abstract: Intestinal commensal bacteria induce protective and regulatory responses that maintain host-microbial mutualism. The contribution of tissue resident commensals to immunity and inflammation at other barrier sites, however, has not been addressed. Here, we report an autonomous role for the skin microbiota in controlling the local inflammatory milieu and tuning resident T lymphocyte function. Protective immunity to a cutaneous pathogen was critically dependent on the skin but not gut microbiota. Furthermore, skin commensals tuned the function of local T cells in a manner dependent on signaling downstream of the interleukin-1 receptor. These findings underscore the importance of the microbiota as a distinctive feature of tissue compartmentalization and provide insight into mechanisms of immune regulation by resident commensal niches in health and disease.

EMR editorial comment: This report shows that skin commensal bacteria play crucial roles in regulating immune functions, just as gut bacteria do. However, the article makes no mention of the implications of its conclusions for the widespread use of triclosan, the active ingredient in antibacterial soaps and toothpaste.  A 2011 NY Times article by Andrew Martin reviews the recent history of concerns about widespread use of triclosan.  A recent CDC study found triclosan in the urine of 75% of Americans over 5 years old.  Several studies find no evidence to support previous concerns that it contributes to antibiotic resistance, however, its effects on hormonal regulation and possible carcinogenicity have led to restrictions on its use in Japan and Canada.  The possibility that it may cause disease by disrupting normal skin commensal bacterial communities has yet to be investigated.   An FDA review of triclosan started in April 2010, and was extended in April 2011.  A ruling is expected  in 2012.