Our bodies are protected against a variety of external factors such as transient pathogens and can preserve homeostasis. This defense mechanism consists of many components, including antimicrobial lipids such as cis-6-hexadecenoic acid (C16:1Δ6) (Wille & Kydonieus, 2003) and sphingosine (Arikawa et al., 2002), as well as antimicrobial peptides such as ┚-defensins and cathelicidin (Harder et al., 2010; Hsu et al., 2009; Tay et al., 2011). The levels of these antimicrobial components in the skin of atopic dermatitis (AD) patients are lower than those of healthy subjects (Arikawa et al., 2002; Harder et al., 2010; Takigawa et al., 2005). It has been reported that the uncommon lipid C16:1Δ6 is present as a major component of sebaceous lipids in human skin and hair but that it is not generally included in plant or animal oils. We have focused on this very unique unsaturated fatty acid, and have been investigating the relationship between this fatty acid and the resident flora of human skin as well as transient pathogens. In the course of that research, we found a correlation between C16:1Δ6 and AD, and have developed a method for the production of C16:1Δ6 on an industrial-scale (Araki et al., 2007; Koike et al., 2000a, 2000b; Takeuchi et al., 1990). In addition, we have made further progress in antimicrobial research involving C16:1Δ6 (Araki et al., 2005) and have selected fatty acid derivatives (oxa-fatty acids) with higher activity by means of analyses of structure-activity relationships (Sugai et al., in preparation). In this chapter, we introduce our research into fatty acids, and we also review approaches to normalizing AD from a microbiological point of view.
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